Fish, method for producing fish, and method for producing fish exhibiting accelerated maturation

Abstract

Provided are fish in which accumulation of inosinic acid is enhanced or accelerated during maturation.　The fish of the present disclosure have loss of function of the ecto-5'-nucleotidase (nt5e) gene.

Description

Fish, fish production method, and method for producing accelerated aging fish

[0001] The present disclosure relates to fish, methods for producing fish, and methods for producing accelerated aging fish.

[0002] After death, nucleic acids in the muscles of fish are decomposed, and it is known that the inosinic acid content in the muscles increases accordingly (Patent Document 1).

[0003] Japanese Unexamined Patent Publication No. 115499 / 1983

[0004] The umami of fish meat is due to inosinic acid, and the umami of the fish can be increased by aging it after death. However, the muscles of the fish soften after death. Therefore, it is currently difficult to obtain fish that is chewy and has a good umami taste.

[0005] Therefore, an object of the present disclosure is to provide fish in which the accumulation of inosinic acid is enhanced or promoted during aging.

[0006] To achieve the above object, the fish of the present disclosure (hereinafter also referred to as "first fish") has a loss-of-function of the ecto-5'-nucleotidase (nt5e) gene.

[0007] The present disclosure is the fish portion of the present disclosure.

[0008] The method for producing fish of the present disclosure (hereinafter also referred to as the "first production method") includes the following step (a): (a) a breeding step of breeding the fish of the present disclosure with other fish.

[0009] The production method disclosed herein is a method for producing fish with accelerated maturation (hereinafter also referred to as the "second production method"), which includes a function-loss step of causing the function of the ecto-5'-nucleotidase (nt5e) gene of the target fish to be lost.

[0010] The enhancement method of the present disclosure is a method for enhancing the inosinic acid content during aging of fish meat, and includes an aging step of aging fish meat, wherein the fish meat is fish meat of a fish of the present disclosure and / or fish meat of an edible portion of a fish of the present disclosure.

[0011] The screening method for fish with accelerated maturation disclosed herein (hereinafter also referred to as the "screening method") includes a selection step of selecting test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost its function from test fish as fish with accelerated maturation.

[0012] The fish production method of the present disclosure (hereinafter also referred to as the "third production method") includes a screening step of screening test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost its function from test fish, and the screening step is carried out by the screening method of the present disclosure.

[0013] The fish of the present disclosure (hereinafter also referred to as the "second fish") is obtained by the first production method, the second production method, or the third production method of the present disclosure.

[0014] The method for detecting the ability to accelerate maturation in fish according to the present disclosure (hereinafter also referred to as the "detection method") includes a detection step of detecting whether the ecto-5'-nucleotidase (nt5e) gene has lost its function in a test fish.

[0015] The processed foods of the present disclosure use the fish of the present disclosure.

[0016] According to the present disclosure, fish can be provided in which the accumulation of inosinic acid is enhanced or promoted during aging.

[0017] Fig. 1 is a graph showing the amount of inosinic acid in medaka fish that have lost the function of the nt5e gene in Example 1. Fig. 2 is a graph showing the amount of inosinic acid in red sea bream that have lost the function of the nt5e gene in Example 2. Fig. 3 is a graph showing the amount of inosinic acid and K value in tilapia that have lost the function of the nt5e gene in Example 3. Fig. 4 is a graph showing the amount of inosinic acid and K value in flounder that have lost the function of the nt5e gene in Example 4.

[0018] <Definitions> As used herein, "fish" refers to animals classified into the group of animals in the subphylum Vertebrata, excluding tetrapods.

[0019] As used herein, "loss of function" refers to, for example, a state in which the original function of a target gene is reduced or lost.

[0020] As used herein, the term "loss of function mutation" refers to a mutation that significantly reduces the inherent function of a gene of interest and / or a mutation that results in a complete loss of function. The "mutation that results in a complete loss of function" can also be referred to as, for example, a null mutation or an amorph.

[0021] As used herein, "fish" refers to individual fish.

[0022] As used herein, "fish part" means a part or portion of an individual fish.

[0023] In the present disclosure, "aging" refers to a process or treatment that breaks down proteins into amino acids in a target fish. The aging can also be referred to as, for example, aging.

[0024] As used herein, the term "inosinic acid decomposition activity" or "inosinic acid decomposition activity" refers to the activity of decomposing inosinic acid into inosine.

[0025] Sequence information for the proteins described herein or the nucleic acids (e.g., DNA or RNA) encoding them is available from Protein Data Bank, UniProt, Ensembl, GenBank, etc. RNA nucleic acid sequences can also be obtained from the corresponding DNA nucleic acid sequences using appropriate sequence conversion software, etc.

[0026] In one aspect, the present disclosure provides a fish in which the accumulation of inosinic acid is enhanced or accelerated during maturation. The fish (first fish) of the present disclosure has a loss-of-function of the ecto-5′-nucleotidase (nt5e) gene.

[0027] As a result of extensive research, the present inventors discovered that fish ecto-5'-nucleotidase (NT5E) is involved in the postmortem fluctuations in the content of umami components in fish. Further research led the present inventors to determine that NT5E contributes to the degradation of inosinic acid, a umami component, and to discover that loss of function of the ecto-5'-nucleotidase (nt5e) gene can promote the accumulation of inosinic acid, leading to the establishment of the present disclosure. According to the present disclosure, the time required to achieve a certain level of inosinic acid content can be shortened compared to fish possessing a wild-type (normal) nt5e gene. Generally, fish become soft and have a soft texture soon after death. For this reason, it is difficult to obtain fish that are chewy yet tasty. On the other hand, according to the present disclosure, the accumulation of inosinic acid in fish meat can be promoted after the death of fish, and it is expected that fish that are chewy and tasty can be obtained.

[0028] Examples of the fish include Tetraodontidae (puffers), Ostraciidae (boxfishes), Sparidae (sea breams and porgies), Salmonidae, Cyprinidae, Serranidae (sea basses), Cichlidae, Oryziidae (medakas), Paralichthys, Carangidae, Bagridae, Clariidae, and Intaluridae.

[0029] Examples of the Tetraodontidae fish include fish of the genus Takifugu, such as Takifugu rubripes, Takifugu porphyreus, and Takifugu niphobles; and fish of the genus Lagocephalus, such as Lagocephalus wheeleri.

[0030] Examples of the fish of the family Oligodontidae include fish of the genus Oligodontidae, such as the boxfish (Ostracion immaculatus).

[0031] Examples of fish of the Sparidae family include fish of the Pagrus genus, such as red sea bream (Pagrus major) and gilthead sea bream (Pagrus auratus); fish of the Acanthopagrus genus, such as black porgy (Acanthopagrus schlegelii) and yellowtail sea bream (Acanthopagrus latus); fish of the Dentex genus, such as yellow sea bream (Dentex tumifrons); and fish of the Sparus genus, such as gilthead sea bream (Sparus aurata).

[0032] Examples of the fish of the Salmonidae family include fish of the genus Salmon, such as rainbow trout (Oncorhynchus mykiss), king salmon (Oncorhynchus tshawytscha), cherry salmon (Oncorhynchus masou), satsukimasu (Oncorhynchus masou), kunimasu (Oncorhynchus kawamurae), pink salmon (Oncorhynchus gorbuscha), and salmon (Oncorhynchus keta); fish of the genus Salmon, such as brown trout (Salmo trutta), sockeye salmon (Oncorhynchus nerka), coho salmon (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar); Dolly Varden trout (Salvelinus malma), char (Salvelinus leucomaenis), and brook trout (Salvelinus fish of the genus Salvelinus such as salmon (Salvelinus fontinalis), lake trout (Salvelinus namaycush), etc.; fish of the genus Sakhalin such as Japanese huchen (Parahucho perryi); and the like.

[0033] Examples of the fish of the Cyprinidae family include fish such as Honmoroko (Gnathopogon caerulescens), Silver carp (Hypophthalmichthys molitrix), Common carp (Cyprinus carpio), Grass carp (Ctenopharyngodon idellus), Bighead carp (Hypophthalmichthys nobilis), European crucian carp (Carassius carassius), Cutlassfish (Cyprinus catla), Japanese bluefin tuna (Mylopharyngodon piceus), Japanese cheetah (Cirrhinus molitorella), Mrigal carp (Cirrhinus cirrhosus), Cutlassfish (Catla catla), Rohita (Labeo rohita), and Slenderhead bream (Megalobrama amblycephala).

[0034] Examples of the fish of the family Grouper include the white spotted grouper (Epinephelus septemfasciatus), grouper (Epinephelus bruneus), red spotted grouper (Epinephelus akaara), yellow spotted grouper (Epinephelus malabaricus), white grouper (Epinephelus aeneus), black spotted grouper (Epinephelus amblycephalus), spotted grouper (Epinephelus areolatus), yellow spotted grouper (Epinephelus bleekeri), white spotted grouper (Epinephelus bontoides), (Epinephelus chlorostigma), orange spotted grouper (Epinephelus coiodes), red spotted grouper (Epinephelus fasciatus), red spotted grouper (Epinephelus fuscoguttatus), starry grouper (Epinephelus labriformis), and grouper (Epinephelus Examples include fish of the Epinephelus genus, such as the yellow spotted grouper (Epinephelus lanceolatus), white spotted grouper (Epinephelus maculatus), yellow spotted grouper (Epinephelus malabricus), dusky grouper (Epinephelus marginatus), striated grouper (Epinephelus ongus), spotted grouper (Epinephelus polyphekadion), yellow spotted grouper (Epinephelus quoyanus), black fin grouper (Epinephelus sexfasciatus), Nassau grouper (Epinephelus striatus), single-spotted grouper (Epinephelus tauvina), and potato grouper (Epinephelus tukula); fish of the grouper genus, such as the yellow spotted grouper (Cromileptes altivelis); and Plectropomus genus, such as the striped grouper (Plectropomus leopardus), as well as hybrids between grouper species.

[0035] Examples of the fish of the Cichlidae family include fish of the Oreochromis genus, such as Nile tilapia (Oreochromis niloticus), cichlid fish (Oreochromis mossambicus), and blue tilapia (Oreochromis aureus).

[0036] Examples of the fish of the medaka family include fish of the genus Oryzias, such as medaka (Oryzias latipes, Oryzias sakaizumii) and Java medaka (Oryzias javanicus).

[0037] Examples of the fish of the family Paralichthyidae include fish of the genus Paralichthys, such as Japanese flounder (Paralichthys olivaceus).

[0038] Examples of the fish of the Carangidae family include fish of the Seriola genus, such as yellowtail amberjack (Seriola lalandi) and amberjack (Seriola dumerili).

[0039] Examples of the fish of the family Lagilidae include fish of the genus Pelteobagrus, such as the Korean bagfish (Pseudobagrus fulvidraco).

[0040] Examples of the fish of the Siluridae family include fish of the Clarias genus, such as the fin catfish (Clarias garienpinus).

[0041] Examples of the fish of the Siluridae family include fish of the genus Ictalurus, such as the channel catfish (Ictalurus punctatus).

[0042] In the present disclosure, the fish may be a fixed species or a hybrid, such as a hybrid resulting from intergeneric hybridization.

[0043] In the present disclosure, the fish is preferably, for example, aquaculture fish.

[0044] In the present disclosure, the fish may be a saltwater fish, a freshwater fish, or a brackish water fish.

[0045] In the present disclosure, the growth stage of the fish is not particularly limited, and may be, for example, any of larvae (juveniles), fry, immature fish (young fish, young fish), and adult fish.

[0046] The ecto-5'-nucleotidase (nt5e) is generally known as a protein having the activity of catalyzing a chemical reaction that converts extracellular 5'-ribonucleotides into ribonucleosides. In fish, two or more types of the nt5e gene and its homologous genes exist in the genome.

[0047] In the present disclosure, the fish nt5e gene may be a gene encoding an ecto-5'-nucleotidase present in fish (wild-type nt5e gene), and specific examples include the nt5e genes shown in Table 1 below.

[0048]

[0049] Specific examples of the nt5e gene (wild-type nt5e gene) of the fish, when the fish is red sea bream, tiger pufferfish, tilapia, rainbow trout, honmoroko, flounder, catfish, or medaka, include the polynucleotides (Pn), (Pt), (Po), (Pm), (Pg), (Pp), (Pq), and (Pl) below, or genomic regions encoding these, respectively. Note that the nucleotide sequences of SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, and 25 below are nucleotide sequences containing a stop codon.

[0050] (Pn) any one of the following polynucleotides (Pn1) to (Pn7): (Pn1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 1; (Pn2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2; (Pn6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 2; (Pn7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 2.

[0051]

[0052] In the (Pn1), the nucleotide sequence of SEQ ID NO: 1 is a nucleotide sequence that encodes the amino acid sequence of the (Pn5). The nucleotide sequence of SEQ ID NO: 1 can be obtained from, for example, red sea bream (Pagrus major).

[0053] In (Pn2), "one or several" may refer to, for example, a range in which the protein encoded by the polynucleotide of (Pn2) has inosinic acid decomposition activity. The "one or several" in (Pn2) refers to, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Pn1). In the present disclosure, a numerical range for the number of bases or amino acids, etc., discloses, for example, all positive integers within that range. That is, for example, the description "1 to 5" means the disclosure of all of "1, 2, 3, 4, and 5" (the same applies hereinafter).

[0054] In the (Pn3), the "identity" may be, for example, within a range in which the protein encoded by the polynucleotide of the (Pn3) has inosinic acid decomposition activity. The identity of the (Pn3) relative to the base sequence of the (Pn1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more. The "identity" can be determined by aligning two base sequences or amino acid sequences (the same applies below). The alignment can be calculated using, for example, BLAST, FASTA, or the like with default parameters.

[0055] In (Pn4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pn4) has inosinic acid decomposition activity. In (Pn4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pn1). The hybridization can be detected by, for example, various hybridization assays. The hybridization assay is not particularly limited, and may be, for example, a hybridization assay described in "Molecular Cloning: A Laboratory Manual 2nd Edition" edited by Sambrook et al. nd Alternatively, the method described in "Cold Spring Harbor Laboratory Press (1989)" or the like can be employed.

[0056] In (Pn4), "stringent conditions" may be, for example, low stringency conditions, moderate stringency conditions, or high stringency conditions. "Low stringency conditions" are, for example, 5x SSC, 5x Denhardt's solution, 0.5% SDS, 50% formamide, and 32°C. "Medium stringency conditions" are, for example, 5x SSC, 5x Denhardt's solution, 0.5% SDS, 50% formamide, and 42°C. "High stringency conditions" are, for example, 5x SSC, 5x Denhardt's solution, 0.5% SDS, 50% formamide, and 50°C. Those skilled in the art can set the degree of stringency by appropriately selecting conditions such as temperature, salt concentration, probe concentration and length, ionic strength, and time. The "stringent conditions" are, for example, those described in the aforementioned "Molecular Cloning: A Laboratory Manual 2nd Edition" edited by Sambrook et al. nd The conditions described in "Cold Spring Harbor Laboratory Press (1989)" can also be used.

[0057] The polynucleotide (Pn5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pn5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pn5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 2.

[0058] Amino acid sequence of NT5E protein of red sea bream (SEQ ID NO: 2) MGALRPRCLHLLLLLLGFSVSTSAAWDLVLLHTNDVHARVEETSKHSGKCSSSRKSGGCFAGVARRATMIKKIRSTDSNVLLLDAGDQFQGSVWFNYYKGAEAAHFMNKLQYDAMALGNHEFDNGVEGLMKPFMEKIRCPVLSANIKPDEAMAPTFSSSYLPYKILTVGSEKVGVVGYTSQETPALSRPGPHLEFEDEVTSLQLQVNKLQTLGVNKIIALGHSGFTVDREIAKKVRGVDVVIGGHTNTFLFTGHPPSSEVPLGSYPFMVTSVDGRQVPVVQAYAFGKYLGHL KVTFDDAGNVMKSTGNPILLDSSVPQDPDVLADVEEWKKSLANYSAQEVGKTLVFLNGTTEECRFRECNLGNLICDAMVNNNIRFLEDEQWNHVSASIFNGGGIRTSIDEHSRNGSITMEDLISVLPFGGTFDLVQLNGSTLRRAF EHSVKRYGESTGEFLQVSGFHVEFDLSKPAGSRVRSLDILCTQCRVPQYEPVEDETVYTVVVPSFMVTGGDGYSMIRNETLKHNSGNLDISVVSNYIMQRKRVYPAVEGRIKIYNSASGPRGQILLVSLVLLWTLWEHVGVTSTSF

[0059] In (Pn6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pn6) has inosinic acid decomposition activity. The "one or several" in (Pn6) may be, for example, 1 to 116, 1 to 86, 1 to 58, 1 to 29, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 2.

[0060] In the (Pn7), the "identity" with respect to the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pn7) has inosinate decomposition activity, for example. The identity of (Pn7) to the amino acid sequence of SEQ ID NO: 2 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0061] (Pt) any of the following polynucleotides (Pt1) to (Pt7): (Pt1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 3; (Pt2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 4; (Pt7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 4.

[0062]

[0063] In (Pt1), the base sequence of SEQ ID NO: 3 is a base sequence that encodes the amino acid sequence of (Pt5). The base sequence of SEQ ID NO: 3 can be obtained from, for example, pufferfish (Takifugu rubripes).

[0064] In (Pt2), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (Pt2) has inosinic acid decomposition activity. The "one or several" in (Pt2) may be, for example, 1 to 348, 1 to 261, 1 to 174, 1 to 87, 1 to 69, 1 to 52, 1 to 34, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Pt1).

[0065] In (Pt3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Pt3) has inosinate decomposition activity. The identity of (Pt3) to the base sequence of (Pt1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0066] In (Pt4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pt4) has inosinate decomposition activity. In (Pt4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pt1). In (Pt4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0067] The polynucleotide (Pt5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pt5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pt5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 4.

[0068] Amino acid sequence of NT5E protein of tiger pufferfish (SEQ ID NO: 4) MSVWSRRCALWVCISLLAGPVWTFELTLLHTNDNHARIEETSEDLGKCSSRGPCFAGVARRFTKVSEIRKKEKNVLFLDAGDQFQGTVWFNYYKGAEAAHFMNKLGYNAMALGNHEFDNGVEGLLPFLQNVNCSVVSANIQPDQSLAAKLSGFLQPYTVLNVGSEKVAVVGYTTAETPFLSMPGPHLKFNEEVEALQVQVDKLETLGYDKIIALGHSGFDVDQQIAKRVRGVDVVIGGHTNTFLYTGKAPSTEVPVGPYPFIVRSDDGRNVPVVQAFAFGKYLGYLRVT FDDAGKVIKAAGNPILLDSSVPQDPDVLAEVNRWKKDLAQYSSQYVGQTLVYLNGTFEECRFRECNLGNLICDGMIDHNIKFSSELQWNHVSLCMLNSGAIRAPIDERYKNGSITMEDVLTVLPFGGTVDLVQIKGSTVKKAFEH AVHRFGSMSGEFLQVSGFHVKYDLSKPVNQRVTSLSALCTECRVPKYEPIDPERTYKVTMPSYLVDGGDGFSMIKEELLKHNTGDLDISVFSKYISQQKRVYPAVEGRITVRGSASSAAHSLDVFLHTWPLLPYISPGSLKDKWL

[0069] In (Pt6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pt6) has inosinic acid decomposition activity. The "one or several" in (Pt6) may be, for example, 1 to 115, 1 to 86, 1 to 57, 1 to 28, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 4.

[0070] In the (Pt7), the "identity" with respect to the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pt7) has inosinate decomposition activity, for example. The identity of (Pt7) to the amino acid sequence of SEQ ID NO: 4 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0071] (Po) any one of the following polynucleotides (Po1) to (Po7): (Po1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 5; (Po2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides are deleted, substituted, inserted and / or added in the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6; (Po7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 6.

[0072]

[0073] In the (Po1), the base sequence of SEQ ID NO: 5 is a base sequence that encodes the amino acid sequence of the (Po5). The base sequence of SEQ ID NO: 5 can be obtained from, for example, tilapia (Oreochromis niloticus).

[0074] In (Po2), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (Po2) has inosinic acid decomposition activity. The "one or several" in (Po2) may be, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Po1).

[0075] In (Po3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Po3) has inosinate decomposition activity. The identity of (Po3) to the base sequence of (Po1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0076] In (Po4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Po4) has inosinate decomposition activity. In (Po4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Po1). In (Po4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0077] The polynucleotide (Po5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Po5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Po5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 6.

[0078] Amino acid sequence of tilapia NT5E protein (SEQ ID NO: 6): MCYTFLVTNAFFTHGDIMGFRSSRRALLTSLCLVLNCWSGASTFELTILHTNDNHARIEETGKDSGKCRPERPCFAGVARRFTKVTEIRTKETNVVFLDAGDQFQGTLWFNYYKGAEAAHFMNKLCYDVMAFGNHEFDNGVEGLIHPFLQNINFSVVSANIKPDYTLAELHKYYSPYKVISVGSEKVAVVGYTSAETPFLSMPGKHLKFEDEVESLQAQVNKLESLGYNKIIALGHSGFVVDQDIARRVRGVDVVVGGHTNTFLYTGTPPSSEVPAGPYPFIVKSSHGRDVP VVQAYAFGKYLGHLKVTFDDAGNVIKAVGNPILMDSSIPQDAEILADVNKWKTDLAQYSTKYVGQTLVYLNGSFEECRFRECNLGNLICDAMVYHNMRHSTGEQWNHVSLCMLNSGGIRTAIDERYRNGSITMEILTVLPFGTC DLVQIKGSTIKKAFEHSVHRYGSKTGEFLQVVYDLSKPVNQRVASLSLLCTECRVPKYEPLDPQKTYTVVMPSYMVGGGDNFTMIKRELLKHNSGDLDITVFSKYISDMKRVFPAVEGRITFRNSAVIASYSIGLLLLSLCLSVTL

[0079] In (Po6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Po6) has inosinic acid decomposition activity. The "one or several" in (Po6) may be, for example, 1 to 116, 1 to 87, 1 to 58, 1 to 29, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 6.

[0080] In the (Po7), the "identity" with respect to the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Po7) has inosinate decomposition activity, for example. The identity of (Po7) to the amino acid sequence of SEQ ID NO: 6 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0081] (Pm) any one of the following polynucleotides (Pm1) to (Pm7): (Pm1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 7; (Pm2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pm1), and encoding a protein having inosinic acid decomposition activity; (Pm3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pm1), and encoding a protein having inosinic acid decomposition activity; (Pm4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pm1), and encoding a protein having inosinic acid decomposition activity; (Pm5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 8; (Pm6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids are deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 8; (Pm7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 8.

[0082]

[0083] In the (Pm1), the nucleotide sequence of SEQ ID NO: 7 is a nucleotide sequence encoding the amino acid sequence of the (Pm5). The nucleotide sequence of SEQ ID NO: 7 can be obtained from, for example, rainbow trout (Oncorhynchus mykiss).

[0084] In (Pm2), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (Pm2) has inosinate decomposition activity. The "one or several" in (Pm2) may be, for example, 1 to 327, 1 to 245, 1 to 163, 1 to 81, 1 to 65, 1 to 49, 1 to 32, 1 to 16, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Pm1).

[0085] In the (Pm3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Pm3) has inosinate decomposition activity. The identity of (Pm3) to the base sequence of (Pm1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0086] In (Pm4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pm4) has inosinate decomposition activity. In (Pm4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pm1). In (Pm4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0087] The polynucleotide (Pm5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pm5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pm5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 8.

[0088] Amino acid sequence of rainbow trout NT5E protein (SEQ ID NO: 8): MKKGNQHIMYAPKIIPNVLVAFLSLAAEILFFSKSASDTVTFTWFSLAEEPVSPEWVSCLPHCKGDVDATDPGEFVTRRAEAFGNHEFDNGVEGLLRPFLQKVNFTVLSANIKADATLAPTINGYYQPYTTFTMGSEIVAVVGYTSVETPVLSLPGPHLIFEDEIKALQVQVDKLITLGYNKIIALGHSGFDVDIDIAKRVKGVDLVIGGHTNTFLYTGSVPSSEVPAGPYPFTVRSEDGRDVPVVQAFAFGKYLGYLKLVFDKSGNVLKAN GNPILLDSSIAQDPGILADVDEWKKNLAQYSSQYVGKTLVYLNGTFNECRFRECNLGNLICDAMIHHNIKYADEIQWNHVSLCILNSGGIRTGIDESHKNGTITMEEVISVLPFGGTFDLVQLKGSTLKKAFENSV RRYGSSRGEFLQVSGIHVEYDLSRSVGDRVTSLSLRCSQCRVPRYESLDPDRLYKLVLPSYIADGGDGFTMIKEEKLKHDTGDLDISVFANYIKEMKRVYPTVEGRIKFRNSSVAAGANCLTLLLLGLMWALSTSL

[0089] In (Pm6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pm6) has inosinate decomposition activity. For example, the "one or several" in (Pm6) may be, for example, 1 to 108, 1 to 81, 1 to 54, 1 to 27, 1 to 21, 1 to 16, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 8.

[0090] In the (Pm7), the "identity" with respect to the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pm7) has inosinate decomposition activity, for example. The identity of (Pm7) to the amino acid sequence of SEQ ID NO: 8 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0091] (Pg) any of the polynucleotides (Pg1) to (Pg7) below: (Pg1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 9; (Pg2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pg1), and encoding a protein having inosinic acid decomposition activity; (Pg3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pg1), and encoding a protein having inosinic acid decomposition activity; (Pg4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pg1), and encoding a protein having inosinic acid decomposition activity; (Pg5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 10; (Pg6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids are deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 10; (Pg7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 10.

[0092]

[0093] In the (Pg1), the nucleotide sequence of SEQ ID NO: 9 is a nucleotide sequence encoding the amino acid sequence of the (Pg5). The nucleotide sequence of SEQ ID NO: 9 can be obtained from, for example, the Japanese dace (Gnathopogon caerulescens).

[0094] In (Pg2), the term "one or several" may refer to, for example, a range in which the protein encoded by the polynucleotide of (Pg2) has inosinate decomposition activity. The term "one or several" in (Pg2) refers to, for example, 1 to 342, 1 to 256, 1 to 171, 1 to 85, 1 to 68, 1 to 51, 1 to 34, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Pg1).

[0095] In (Pg3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Pg3) has inosinate decomposition activity. The identity of (Pg3) to the base sequence of (Pg1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0096] In (Pg4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pg4) has inosinate decomposition activity. In (Pg4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pg1). In (Pg4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0097] The polynucleotide (Pg5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pg5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pg5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 10.

[0098] Amino acid sequence of NT5E protein of Honmoroko (SEQ ID NO: 10): MMAQWLSSISLLWIHCQLCRTAEFELTLLHTNDVHARVEETNKDSGKCSKAPCFAGVARRLTKIREVRAQEKHVLLLDAGDQFQGTVWFNFYKGAEAAYFMNKLGYNAMALGNHEFDNGVDGLVKPFLQEVNCSVLSANIKADQTIAPRISGYYLPYKIFNFTSEKVGVVGYTSVETPALSLPGPHLQFEDEVTALQLQVDKLTALGVNKIIALGHSGFLTDKKIAKKVRGVDVVIGGHTNTFLFTGEPPSTEVPAGPYPFMVDSEDGRQVPVVQAYAFGKYLGF LKVTFDSNGNVVKSFGNPILLNGSVAPDPVIQAEVDNWRKNLANYSSQYVGETLVYLNGTFEECRFRECNLGNLICDAMVHNNIKYADEIQWNHVSSCILNGGAIRSPIDERNRNGSITMEDLIAVLPFGGTFDLVQMNGST LREVFEHSVRRYGGNTGEFLQVSGFQLVFDLSKPPGSRVKSVNALCTECRVPRYEPLIPTKVYKVVLPSYLVDGDGYTMIKEQKLKHDSGDLDIAVVASYITERKRVHPAVEGRIQFSSSCIAHRGYTAIVLLVWALWVMIV

[0099] In (Pg6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pg6) has inosinate decomposition activity. The "one or several" in (Pg6) may be, for example, 1 to 114, 1 to 85, 1 to 57, 1 to 28, 1 to 22, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 10.

[0100] In the (Pg7) polynucleotide, the "identity" with respect to the amino acid sequence may be within a range in which the protein encoded by the (Pg7) polynucleotide has inosinate decomposition activity, for example, the identity of the (Pg7) polynucleotide to the amino acid sequence of SEQ ID NO: 10 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0101] (Pp) any of the polynucleotides (Pp1) to (Pp7) below: (Pp1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 11; (Pp2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides are deleted, substituted, inserted and / or added in the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 12; (Pp6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids are deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 12; (Pp7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 12.

[0102]

[0103] In (Pp1), the nucleotide sequence of SEQ ID NO: 11 is a nucleotide sequence encoding the amino acid sequence of (Pp5). The nucleotide sequence of SEQ ID NO: 11 can be obtained from, for example, olive flounder (Paralichthys olivaceus).

[0104] In (Pp2), the term "one or several" may refer to, for example, a range in which the protein encoded by the polynucleotide of (Pp2) has inosinic acid decomposition activity. The term "one or several" in (Pp2) means, for example, 1 to 234, 1 to 175, 1 to 117, 1 to 58, 1 to 47, 1 to 35, 1 to 23, 1 to 11, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Pp1).

[0105] In (Pp3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Pp3) has inosinate decomposition activity. The identity of (Pp3) to the base sequence of (Pp1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0106] In (Pp4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pp4) has inosinate decomposition activity. In (Pp4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pp1). In (Pp4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0107] The polynucleotide (Pp5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pp5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pp5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 12.

[0108] Amino acid sequence of NT5E protein of flounder (SEQ ID NO: 12): SGPHLRFEDEVDALQPHVDKLRTLGVDKIIALGHSGFTKDQEIAKKVRGVDVVIGGHTNTFLYTGTPPSSEVPAGPYPFLVKSDDGRQVPVVQAYAFGKYLGYLKVTFDDAGNVERATGNPILLNSSFPQDPDVLADVEKWKKNLANYSAQVVGQTLVFLNGESEECRFRECNLGNLICDAMVDNNIRIPDDVQWNHVSASIFNGGGVRASIDEQSRNGSITMEDLISVLPFGGTFDLVQLRGSTLRKAFEHSVRRYGQSTGEFLQVSGFHVEFDLSKPPGRRVTSLRILCTECRVPHYQPVEDETVYTVVLTSYMVKGGDGFDMIQNEIVKYNSGDLDISVVSRFIGKRKKVYPPVEGRIRIKNSASRLQGRAALLVSLSLLWSVCGTM

[0109] In (Pp6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pp6) has inosinate decomposition activity. The "one or several" in (Pp6) may be, for example, 1 to 78, 1 to 58, 1 to 39, 1 to 19, 1 to 15, 1 to 11, 1 to 7, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 12.

[0110] In (Pp7), the "identity" of the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pp7) has inosinate decomposition activity, for example, the identity of (Pp7) to the amino acid sequence of SEQ ID NO: 12 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0111] (Pq) any of the following polynucleotides (Pq1) to (Pq7): (Pq1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 25; (Pq2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides are deleted, substituted, inserted and / or added in the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 26; (Pq7) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 26.

[0112]

[0113] In the (Pq1), the nucleotide sequence of SEQ ID NO: 25 is a nucleotide sequence encoding the amino acid sequence of the (Pq5). The nucleotide sequence of SEQ ID NO: 25 can be obtained from, for example, the catfish (Clarias garienpinus).

[0114] In (Pq2), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (Pq2) has inosinate decomposition activity. The "one or several" in (Pq2) may be, for example, 1 to 370, 1 to 277, 1 to 185, 1 to 92, 1 to 74, 1 to 55, 1 to 37, 1 to 18, 1 to 9, 1 to 3, 1 or 2, or 1 in the base sequence of (Pq1).

[0115] In the (Pq3), the "identity" may be within a range in which the protein encoded by the polynucleotide of (Pq3) has inosinate decomposition activity. The identity of (Pq3) to the base sequence of (Pq1) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0116] In (Pq4), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (Pq4) has inosinate decomposition activity. In (Pq4), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (Pq1). In (Pq4), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0117] The polynucleotide (Pq5) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (Pq5) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (Pq5) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 26.

[0118] Amino acid sequence of NT5E protein of longfin catfish (SEQ ID NO: 26): MRYSTAARALLPLLVVCASLRLAAADWELTLLHTNDVHARVEETNKDSGKCTKGECFAGVARRSTKIKEIRSKEKNVLLLDAGDQFQGTVWFNVYKGDEAAHFMNKLQYDAMALGNHEFDNRVEGLIPFLQKVKCPVLSANIKAVEPVASNISGYFSPYKILNVTSEKVGIVGYTTKETPALSLPGPYLHFEDEVVAVQREVDKLIALGVNKIIALGHSGFDTDKEIAKKVRGVDVVIGGHTNTFLYTGAPPSSEVPAGPYPLMVQSDDGRKVPVVQAYAFGKYLGYLKVTFDSAGNVIKAEGNPILL NSSVTEDPSIKADVDTWKVKLANYSAQFVGNTLVYLNGTFEECRFRECNLGNLICDAMVHHYIKYPDELQWNHVSSCILNGGGIRSSIDERSRNGSITMEDVLTVLPFGTYDLVQLNGSTLLQAFEHSVHRYGGNTGEFLQVSGFQLEYDLTK PSGHRVIKARVLCTECRVPHYEPLDATKVYRVVMPSYLVDGDGFSMIKQQILKHDSGDLDISVFSRYITERQRVHPSVEGRIRLLNSAVEISNSSSYTLCVVILIIVGVMLIMLAGVYYYRRKGLVDDKVTVQYRRAIDGDEKLNDQTTVTSS

[0119] In (Pq6), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pq6) has inosinate decomposition activity. The "one or several" in (Pq6) may be, for example, 1 to 123, 1 to 92, 1 to 61, 1 to 30, 1 to 24, 1 to 18, 1 to 12, 1 to 6, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 26.

[0120] In the (Pq7), the "identity" of the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (Pq7) has inosinate decomposition activity, for example. The identity of (Pq7) to the amino acid sequence of SEQ ID NO: 26 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0121] (Pl) A polynucleotide selected from any of the following (Pl1) to (Pl7): (Pl1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 13; (Pl2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pl1), and encoding a protein having inosinic acid decomposition activity; (Pl3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pl1), and encoding a protein having inosinic acid decomposition activity; (Pl4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Pl1), and encoding a protein having inosinic acid decomposition activity; (Pl5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 14; (P16) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence in which one or several amino acids are deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 14; (P17) A polynucleotide that encodes a protein having inosinic acid decomposition activity, which consists of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 14.

[0122]

[0123] In the (P11), the nucleotide sequence of SEQ ID NO: 13 is a nucleotide sequence encoding the amino acid sequence of the (P15). The nucleotide sequence of SEQ ID NO: 13 can be obtained from, for example, medaka (Oryzias latipes).

[0124] In (P12), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (P12) has inosinic acid decomposition activity. The "one or several" in (P12) may be, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (P11).

[0125] In the (P13), the "identity" may be within a range in which the protein encoded by the polynucleotide of (P13) has inosinate decomposition activity. The identity of (P13) to the base sequence of (P11) is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0126] In (P14), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (P14) has inosinate decomposition activity. In (P14), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (P11). In (P14), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0127] The polynucleotide (P15) may have any nucleotide sequence as long as the protein encoded by the polynucleotide (P15) has inosinate decomposition activity. The nucleotide sequence of the polynucleotide (P15) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 14.

[0128] Amino acid sequence of medaka NT5E protein (SEQ ID NO: 14): MTLRWRCCALGALLGLLLRLDSWSGASGFELTLLHTNDVHARIEETSEDSSKCHEAGSCFAGVARMFTKVTEIRRKETHVLFLDAGDQFQGTVWFNYYKGKEAAHFMNKLGYDVMTFGNHEFDNGVDSLTQNFLQRVNFSVVCATIKPLHSLVANMSRFYRPFAVFNVGSEKVAVVGYTTKETPVLSAPGPYLKFEDEVEALQDQVNQLEKLGVNKIIALGHSGFEVDKDIAKRVRGIDVVIGGHTNTFLYTGKPPSTEVPRGPYPFNVSSNDGRWVPVVQAFAFGKY LGYLKVTFDQAGKVVKAVGNPILMNSSIPQDPGILSDVEKWKKGLEQYSSQYIGQTLVYLNGTFEECRFRECNLGNLICDAMIYNYIRYSNKLQWNHVGVCMLNSGSIRATIDERSTNGSITMEEILSVLPFGGTFDLVQLKGS TLKKAFEHSVHRYGGMSGEFLQVSGIRVEYDLSKPVNQRVVSLLMRCTECRVPKFEPLDPQKTYTVVMTSFMVGGGGYSMIQDELLKHNTGNLDTLVFSEYIKDMRVYPAVEGRITFRNSAAFAAAHSLSLMLLSLCLFLNLCM

[0129] In (P16), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (P16) has inosinic acid decomposition activity. The "one or several" in (P16) may be, for example, 1 to 115, 1 to 86, 1 to 57, 1 to 28, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 14.

[0130] In the (P17) polynucleotide, the "identity" of the amino acid sequence may be within a range in which the protein encoded by the (P17) polynucleotide has inosinate decomposition activity, for example, the identity of the (P17) polynucleotide to the amino acid sequence of SEQ ID NO: 14 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0131] In the present disclosure, "inosinic acid decomposition activity" may be evaluated, for example, based on the amount of inosinic acid in a biological sample from a target fish (test fish), or based on the expression of the nt5e gene or NT5E protein in the biological sample from the test fish. The biological sample from the test fish is not particularly limited and may be, for example, either an individual fish or a part of an individual fish of the test fish, preferably fish skeletal muscle. The type of biological sample used may be, for example, one type, or two or more types.

[0132] When the inosinic acid content in the biological sample of the test fish is evaluated, the inosinic acid decomposition activity can be evaluated based on the inosinic acid content in the flesh of fish having a wild-type nt5e gene or a fish having a loss-of-function nt5e gene one day (24 hours) after death. Specifically, the amount of inosinic acid in the biological sample of the test fish 24 hours after death is measured according to Example 1 described below. If the amount of inosinic acid in the biological sample of the test fish is the same as the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form (no significant difference), if it is (significantly) lower than the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form, and / or if it is (significantly) lower than the amount of inosinic acid in the biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as having, for example, inosinic acid decomposition activity. On the other hand, if the amount of inosinic acid in the biological sample of the test fish is (significantly) higher than the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form, if the amount of inosinic acid is the same as (no significant difference from) the amount of inosinic acid in the biological sample of fish that have the loss-of-function form of the nt5e gene in homozygous or heterozygous form, and / or if the amount of inosinic acid is (significantly) higher than the amount of inosinic acid in the biological sample of fish that have the loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as not having, for example, inosinic acid decomposition activity.

[0133] When evaluating based on the expression of the nt5e gene, the expression of the nt5e gene can be detected, for example, by detecting the expression of mRNA of the nt5e gene. Extraction of mRNA from the biological sample of fish can be performed by a conventional method. Detection of the expression of mRNA of the nt5e gene can be performed, for example, by semi-quantitative PCR, quantitative PCR, Northern blotting, digital PCR, RNA sequence analysis (RNAseq), etc. Primers and / or probes used to detect the expression of the mRNA can be designed, for example, by a method commonly used in the art. If the expression level of the nt5e gene in the biological sample of the test fish is the same (no significant difference) as the expression level of the nt5e gene in fish that have the wild-type nt5e gene in homozygous form, if the expression level of the nt5e gene in the biological sample of the test fish is (significantly) higher than the expression level of the nt5e gene in fish that have the wild-type nt5e gene in homozygous form, and / or if the expression level of the nt5e gene in the biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as having, for example, inosinic acid decomposition activity. On the other hand, if the expression level of the nt5e gene in the biological sample of the test fish is (significantly) lower than the expression level of the nt5e gene in a biological sample of fish having the wild-type nt5e gene in homozygous form, if it is the same as (not significantly different from) the expression level of the nt5e gene in a biological sample of fish having a loss-of-function form of the nt5e gene in homozygous or heterozygous form, and / or if it is (significantly) lower than the expression level of the nt5e gene in a biological sample of fish having a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as not having, for example, inosinic acid decomposition activity.

[0134] When evaluation is based on the expression of the NT5E protein, the expression of the NT5E protein can be detected by, for example, a spectrophotometer-based method such as an ultraviolet absorption method or a bicinchoninic acid method, ELISA, Western blotting, etc. The protein-containing extract from the fish can be prepared by a method commonly used in the art, such as ultrasonic disruption or physical disruption using a homogenizer. Furthermore, if the expression level of NT5E protein in the biological sample of the test fish is the same (no significant difference) as the expression level of NT5E protein in fish that have the wild-type NT5E protein in homozygous form, if the expression level of NT5E protein in the biological sample of the test fish is (significantly) higher than the expression level of NT5E protein in fish that have the wild-type NT5E protein in homozygous form, and / or if the expression level of NT5E protein is (significantly) higher than the expression level of NT5E protein in biological samples of fish that have a loss-of-function form of the NT5E protein in homozygous or heterozygous form, the test fish can be evaluated as having, for example, inosinic acid decomposition activity. On the other hand, if the expression level of NT5E protein in the biological sample of the test fish is (significantly) lower than the expression level of NT5E protein in a biological sample of fish that have the wild-type NT5E protein in a homozygous form, if it is the same as (not significantly different from) the expression level of NT5E protein in a biological sample of fish that have a loss-of-function form of NT5E protein in a homozygous or heterozygous form, and / or if it is (significantly) lower than the expression level of NT5E protein in a biological sample of fish that have a loss-of-function form of NT5E protein in a homozygous or heterozygous form, the test fish can be evaluated as not having, for example, inosinic acid decomposition activity.

[0135] In the present disclosure, the nt5e gene may exist in the form of RNA (e.g., mRNA) or DNA (e.g., cDNA or genomic DNA). The DNA may be double-stranded or single-stranded. In the present disclosure, the gene may include additional sequences such as sequences of untranslated regions (UTRs).

[0136] The loss of function of the nt5e gene refers to a state in which the function of the nt5e gene is (significantly) reduced or lost to the extent that the amount of inosinic acid in fish meat increases during fish aging in fish having a loss-of-function form of the nt5e gene, compared to fish having a wild-type nt5e gene (hereinafter also referred to as "wild-type fish"). Specifically, the loss of function of the nt5e gene may refer to, for example, a state in which the expression level of the nt5e gene mRNA or the protein encoded by the gene is (significantly) reduced, or a state in which the nt5e gene mRNA or the protein encoded by the gene is not fully expressed, or a state in which the expression level of functional nt5e gene mRNA or the protein encoded by the nt5e gene is reduced, or a state in which functional nt5e gene mRNA or the protein encoded by the nt5e gene is not fully expressed. Therefore, in the present disclosure, the loss of function of the nt5e gene may be achieved by introducing a loss-of-function mutation into the nt5e gene, or by introducing a polynucleotide that suppresses the expression of the nt5e gene. The "suppression of gene expression" may be suppression of gene transcription or suppression of translation into protein.

[0137] In the present disclosure, the fish in which the nt5e gene has been lost can also be referred to as, for example, fish having a loss-of-function form of the nt5e gene. The fish in which the nt5e gene has been lost can have, for example, a loss-of-function form of the nt5e gene in a heterozygous form or a homozygous form. The fish in which the nt5e gene has been lost can further have genes other than the nt5e gene modified, altered, introduced, and / or lost in function.

[0138] The loss of function of the nt5e gene can be induced, for example, by introducing a mutation, more specifically, a loss-of-function mutation, into the nt5e gene. The type of mutation is not particularly limited, and examples include point mutations, missense mutations, nonsense mutations, frameshift mutations, and large deletions of bases. The mutation may result in, for example, a partial or complete deletion of the nt5e gene. The frameshift mutation is a mutation that occurs when a base is deleted or inserted, resulting in a shift in the triplet reading frame (codon). Compared to base pair substitution mutations, the frameshift mutation has a much greater impact on gene function. This is because the frameshift mutation significantly shifts the genetic code in the gene after the point where the frameshift mutation is introduced, resulting in not only a change in amino acid but also a shift in the stop codon, etc.

[0139] The loss-of-function form of the nt5e gene is, for example, a gene in which a mutation such as insertion, deletion, and / or substitution of one or several bases (hereinafter also referred to as "one or more bases") has been introduced into the base sequence of the wild-type nt5e gene. The one or more bases can be, for example, the same as the explanation of the number of bases in the above-mentioned (Pn2), (Pt2), (Po2), (Pm2), (Pg2), (Pp2), (Pq2), and (Pl2). The frameshift mutation occurs, for example, by insertion or deletion of 3m+1 bases or 3m+2 bases (m is an integer of 0 or more).

[0140] In the present disclosure, mutations in the nt5e gene can be induced, for example, by introducing mutations into a target gene in the genome of a target fish using conventional methods. The method for introducing mutations can be carried out, for example, by homologous recombination; genome editing techniques using ZFN, TALEN, CRISPR-CAS9, CRISPR-CPF1, etc. The method for introducing mutations can also be carried out, for example, by site-directed mutagenesis or other mutagenesis methods. Alternatively, the method for introducing mutations can also be carried out, for example, by random mutagenesis. Examples of random mutagenesis include irradiation treatment with α-rays, β-rays, γ-rays, X-rays, or other radiation; chemical treatment with mutagens such as ethyl methanesulfonate (EMS) or ethynylnitrosourea (ENU); and heavy ion beam treatment. For details on the method for introducing mutations using genome editing technology, see, for example, Example 1 described below. Specifically, the introduction of mutations using genome editing technology can be carried out, for example, by introducing proteins and nucleic acids constituting the genome editing technology, or vectors encoding these. Examples of the protein include CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) enzymes, and specific examples include Cas1, Cas1B, Cas2, Cas3, Cas4, Cas5, Cas6, Cas7, Cas8, Cas9, Cas10, Csy1, Csy2, Csy3, Cse1, Cse2, Csc1, Csc2, Csa5, Csn2, Csm2, and Css3. Examples of the nucleic acid include Csm3, Csm4, Csm5, Csm6, Cmr1, Cmr3, Cmr4, Cmr5, Cmr6, Csb1, Csb2, Csb3, Csx17, Csx14, Csx10, Csx16, CsaX, Csx3, Csx1, Csx15, Csf1, Csf2, Csf3, and Csf4. Examples of the nucleic acid include crRNA and tracrRNA, or single-stranded nucleic acids in which these are linked via a linker. In this case, the nucleic acid is designed, for example, so that the base sequence that anneals to the target sequence in crRNA is complementary to the base sequence encoding the nt5e gene. One type of nucleic acid may be used alone, or two or more types may be used in combination.When the genome editing technique is used, for example, by using two or more types of nucleic acids, a large deletion of the base sequence between target sequences can be induced. The method for introducing the mutation may be carried out by a mutagenesis method such as site-directed mutagenesis.

[0141] The position of the mutation in the loss-of-function mutant of the nt5e gene, i.e., the position at which the mutation is introduced into the nt5e gene, is not particularly limited and can be set in any region related to the nt5e gene. Specific examples of the position of the mutation in the loss-of-function mutant of the nt5e gene include an expression control region such as a promoter region of the nt5e gene, an exon region including a coding region that encodes the protein encoded by the nt5e gene, and a non-coding region (e.g., an intron region, an enhancer region, etc.) that does not encode the protein encoded by the nt5e gene, and preferably an exon region. The exon region is, for example, the first exon.

[0142] As a specific example, when the fish is red sea bream, the position of the mutation in the nt5e gene can be, for example, from bases 1 to 1200, preferably from bases 1000 to 1100, or from bases 1014 to 1036, in the base sequence of SEQ ID NO: 1. The position of the mutation in the nt5e gene is, for example, a position corresponding to exon 6 of the red sea bream nt5e gene. When the fish is tiger pufferfish, the position of the mutation in the nt5e gene can be, for example, from bases 1 to 250, preferably from bases 100 to 200, or from bases 131 to 153, in the base sequence of SEQ ID NO: 3. The position of the mutation in the nt5e gene can be, for example, a position corresponding to exon 1 of the tiger pufferfish nt5e gene. When the fish is tilapia, the position of the mutation in the nt5e gene can be, for example, from bases 1 to 300, preferably from bases 200 to 250, or from bases 217 to 239, in the base sequence of SEQ ID NO: 5. The position of the mutation in the nt5e gene is, for example, a position corresponding to the first exon of the tilapia nt5e gene. When the fish is a flounder, the position of the mutation in the nt5e gene is, for example, a position corresponding to bases 1 to 700, preferably bases 600 to 650, or bases 605 to 627 in the base sequence of SEQ ID NO: 5. The position of the mutation in the nt5e gene is, for example, a position corresponding to exon 4 of the flounder nt5e gene. The mutation introduced at these positions of mutation is preferably a nonsense mutation or a frameshift mutation.

[0143] When the fish is red sea bream, tiger pufferfish, tilapia, rainbow trout, honmoroko, flounder, catfish, or medaka, examples of the loss-of-function form of the nt5e gene of the fish include the following polynucleotides (MN), (MT), (MO), (MM), (MG), (MP), (MQ), and (ML), or genomic regions encoding these, respectively.

[0144] (MN) A polynucleotide selected from any of the following (MN1) to (MN5); (MN1) a polynucleotide consisting of a base sequence in which one or more bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 1; (MN2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 1; (MN3) a polynucleotide consisting of a base sequence that is complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 1; (MN4) a polynucleotide that encodes a protein consisting of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 2; (MN5) a polynucleotide that encodes a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 2.

[0145] The polynucleotides (MN1) to (MN5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0146] In the polynucleotides (MN1) to (MN5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pn1) or (Pn5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0147] The "one or several" in (MN1) means, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 1.

[0148] The identity of (MN2) to the base sequence of SEQ ID NO: 1 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0149] In (MN3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 1. The hybridization can be detected, for example, by various hybridization assays. In (MN3), the hybridization and stringent conditions can be determined as described in (Pn4).

[0150] The "one or several" in (MN4) means, for example, 1 to 116, 1 to 86, 1 to 58, 1 to 29, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 2.

[0151] The identity of (MN5) to the amino acid sequence of SEQ ID NO: 2 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0152] (MT) any of the polynucleotides (MT1) to (MT5) below; (MT1) a polynucleotide consisting of a base sequence in which one or several bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 3; (MT2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 3; (MT3) a polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 3; (MT4) a polynucleotide encoding a protein consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 4; (MT5) a polynucleotide encoding a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 4.

[0153] The polynucleotides (MT1) to (MT5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0154] In the polynucleotides (MT1) to (MT5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pt1) or (Pt5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0155] The "one or several" of (MT1) means, for example, 1 to 348, 1 to 261, 1 to 174, 1 to 87, 1 to 69, 1 to 52, 1 to 34, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 3.

[0156] The identity of (MT2) to the base sequence of SEQ ID NO: 3 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0157] In (MT3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 3. In (MT3), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0158] The "one or several" in (MT4) means, for example, 1 to 115, 1 to 86, 1 to 57, 1 to 28, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 4.

[0159] The identity of (MT5) to the amino acid sequence of SEQ ID NO: 4 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0160] (MO) A polynucleotide selected from any of the following (MO1) to (MO5); (MO1) a polynucleotide consisting of a base sequence in which one or more bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 5; (MO2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 5; (MO3) a polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 5; (MO4) a polynucleotide encoding a protein consisting of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6; (MO5) a polynucleotide encoding a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 6.

[0161] The polynucleotides (MO1) to (MO5) are preferably polynucleotides that encode proteins that do not have inosinic acid decomposition activity.

[0162] In the polynucleotides (MO1) to (MO5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Po1) or (Po5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0163] The "one or several" of (MO1) means, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 5.

[0164] The identity of (MO2) to the base sequence of SEQ ID NO: 5 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0165] In (MO3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 5. In (MO3), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0166] The "one or several" in (MO4) means, for example, 1 to 116, 1 to 87, 1 to 58, 1 to 29, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 6.

[0167] The identity of (MO5) to the amino acid sequence of SEQ ID NO: 6 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0168] (MM) A polynucleotide selected from any of the following (MM1) to (MM5); (MM1) a polynucleotide consisting of a base sequence in which one or more bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 7; (MM2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 7; (MM3) a polynucleotide consisting of a base sequence that is complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 7; (MM4) a polynucleotide that encodes a protein consisting of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 8; (MM5) a polynucleotide that encodes a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 8.

[0169] The polynucleotides (MM1) to (MM5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0170] In the polynucleotides (MM1) to (MM5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pm1) or (Pm5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0171] The "one or several" of (MM1) means, for example, 1 to 327, 1 to 245, 1 to 163, 1 to 81, 1 to 65, 1 to 49, 1 to 32, 1 to 16, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 7.

[0172] The identity of (MM2) to the base sequence of SEQ ID NO: 7 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0173] In (MM3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 7. The hybridization can be detected, for example, by various hybridization assays. In (MM3), the hybridization and stringent conditions can be determined as described in (Pn4).

[0174] The "one or several" in (MM4) means, for example, 1 to 108, 1 to 81, 1 to 54, 1 to 27, 1 to 21, 1 to 16, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 8.

[0175] The identity of (MM5) to the amino acid sequence of SEQ ID NO: 8 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0176] (MG) Any of the polynucleotides (MG1) to (MG5) below; (MG1) A polynucleotide consisting of a base sequence in which one or several bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 9; (MG2) A polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 9; (MG3) A polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 9; (MG4) A polynucleotide that encodes a protein consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 10; (MG5) A polynucleotide that encodes a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 10.

[0177] The polynucleotides (MG1) to (MG5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0178] In the polynucleotides (MG1) to (MG5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pg1) or (Pg5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0179] The "one or several" of (MG1) means, for example, 1 to 327, 1 to 245, 1 to 163, 1 to 81, 1 to 65, 1 to 49, 1 to 32, 1 to 16, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 9.

[0180] The identity of (MG2) to the base sequence of SEQ ID NO: 9 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0181] In (MG3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 9. The hybridization can be detected, for example, by various hybridization assays. In (MG3), the hybridization and stringent conditions can be determined as described in (Pn4).

[0182] The "one or several" in (MG4) means, for example, 1 to 108, 1 to 81, 1 to 54, 1 to 27, 1 to 21, 1 to 16, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 10.

[0183] The identity of (MG5) to the amino acid sequence of SEQ ID NO: 10 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0184] (MP) Any of the polynucleotides (MP1) to (MP5) below; (MP1) A polynucleotide consisting of a base sequence in which one or more bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 11; (MP2) A polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 11; (MP3) A polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 11; (MP4) A polynucleotide encoding a protein consisting of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 12; (MP5) A polynucleotide encoding a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 12.

[0185] The polynucleotides (MP1) to (MP5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0186] In the polynucleotides (MP1) to (MP5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pg1) or (Pg5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0187] The "one or several" of (MP1) means, for example, 1 to 327, 1 to 245, 1 to 163, 1 to 81, 1 to 65, 1 to 49, 1 to 32, 1 to 16, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 11.

[0188] The identity of (MP2) to the base sequence of SEQ ID NO: 11 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0189] In (MP3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 11. The hybridization can be detected, for example, by various hybridization assays. In (MP3), the hybridization and stringent conditions can be determined as described in (Pn4).

[0190] The "one or several" of (MP4) means, for example, 1 to 108, 1 to 81, 1 to 54, 1 to 27, 1 to 21, 1 to 16, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 12.

[0191] The identity of (MP5) to the amino acid sequence of SEQ ID NO: 12 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0192] (MQ) A polynucleotide selected from any of the following (MQ1) to (MQ5); (MQ1) a polynucleotide consisting of a base sequence in which one or more bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 25; (MQ2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 25; (MQ3) a polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 25; (MQ4) a polynucleotide encoding a protein consisting of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 25; (MQ5) a polynucleotide encoding a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 26.

[0193] The polynucleotides (MQ1) to (MQ5) are preferably polynucleotides that encode proteins that do not have the activity of decomposing inosinic acid.

[0194] In the polynucleotides (MQ1) to (MQ5), "not having inosinic acid decomposition activity" means, for example, that the inosinic acid decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pq1) or (Pq5), and preferably means that the inosinic acid decomposition activity is completely lost.

[0195] The "one or several" in (MQ1) means, for example, 1 to 370, 1 to 277, 1 to 185, 1 to 92, 1 to 74, 1 to 55, 1 to 37, 1 to 18, 1 to 9, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 25.

[0196] The identity of (MQ2) to the base sequence of SEQ ID NO: 25 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0197] In (MQ3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 25. In (MQ3), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0198] The "one or several" in (MQ4) means, for example, 1 to 123, 1 to 92, 1 to 61, 1 to 30, 1 to 24, 1 to 18, 1 to 12, 1 to 6, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 26.

[0199] The identity of (MQ5) to the amino acid sequence of SEQ ID NO: 26 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0200] (ML) A polynucleotide selected from any of the following (ML1) to (ML5); (ML1) a polynucleotide consisting of a base sequence in which one or several bases have been deleted, substituted, inserted and / or added in the base sequence of SEQ ID NO: 13; (ML2) a polynucleotide consisting of a base sequence that is 80% or more identical to the base sequence of SEQ ID NO: 13; (ML3) a polynucleotide consisting of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of SEQ ID NO: 13; (ML4) a polynucleotide encoding a protein consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 14; (ML5) a polynucleotide encoding a protein consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 14.

[0201] The polynucleotides (ML1) to (ML5) are preferably polynucleotides that encode proteins that do not have inosinic acid decomposition activity.

[0202] In the polynucleotides (ML1) to (ML5), "not having inosinate decomposition activity" means, for example, that the inosinate decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (P11) or (P15), and preferably means that the inosinate decomposition activity is completely lost.

[0203] The "one or several" of (ML1) means, for example, 1 to 351, 1 to 263, 1 to 175, 1 to 87, 1 to 70, 1 to 52, 1 to 35, 1 to 17, 1 to 8, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of SEQ ID NO: 13.

[0204] The identity of (ML2) to the base sequence of SEQ ID NO: 13 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0205] In (ML3), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide consisting of the base sequence of SEQ ID NO: 13. In (ML3), the hybridization and stringent conditions can be the same as those described in (Pn).

[0206] The "one or several" in (ML4) means, for example, 1 to 115, 1 to 86, 1 to 57, 1 to 28, 1 to 23, 1 to 17, 1 to 11, 1 to 8, 1 to 6, 1 to 5, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 14.

[0207] The identity of (ML5) to the amino acid sequence of SEQ ID NO: 14 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0208] As another example, when the fish is a medaka, examples of the loss-of-function form of the nt5e gene of the fish include the polynucleotide (M1) below or a genomic region encoding the same.

[0209] (Ml) any of the polynucleotides (Ml1) to (Ml7) below: (Ml1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 15; (Ml2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Ml1), and encoding a protein that does not have inosinic acid decomposition activity; (Ml3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Ml1), and encoding a protein that does not have inosinic acid decomposition activity; (Ml4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the nucleotide sequence of (Ml1), and encoding a protein that does not have inosinic acid decomposition activity; (Ml5) a polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 16; (M16) A polynucleotide encoding a protein that does not have inosinic acid decomposition activity, consisting of an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 16; (M17) A polynucleotide encoding a protein that does not have inosinic acid decomposition activity, consisting of an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 16.

[0210] In the polynucleotides (Ml1) to (Ml7), "not having inosinate decomposition activity" means, for example, that the inosinate decomposition activity is significantly suppressed compared to the protein encoded by the polynucleotide (Pl1) or (Pl5), and preferably means that the inosinate decomposition activity is completely lost.

[0211] Nucleotide sequence of a loss-of-function mutant of medaka nt5e gene (SEQ ID NO: 15): 5'-ATGACTCTCCGCTGGCGCTGCTGCGCCCTCGGCGCCTTGCTCGGTCTCCTTCTCCGGTTAGACTCGTGGAGCGGAGCGTCCGGCTTCGAGCTGACTCTGCTCCACACCAACGACGTCCACGCTCGCATCGAGGAGACCAGCGAGGACTCGTCCAAATGCCACGAAGCGGGCTCGTGCTTCGCGGGGGTCGCCAGGATGTTCACCAAAGACGGAGATCCGGAGAAAGGAGACGCACGTGCTGTTTCTGGACGCTGGAGATCAATTTCAAGGCACGGTGTGGTTCAACTACTACAAAGGCAAAGAAGCTGCGCATTTCATGAACAAACTTGGTTATGA-3'

[0212] In the (Ml1), the nucleotide sequence of SEQ ID NO: 15 is a nucleotide sequence in which the 208th and 209th bases and the 339th to 1734th bases are deleted from the nucleotide sequence of SEQ ID NO: 13. The nucleotide sequence of SEQ ID NO: 15 is a nucleotide sequence that encodes the amino acid sequence of (Ml5).

[0213] In (Ml2), the "one or several" may be within a range in which the protein encoded by the polynucleotide of (Ml2) does not have inosinic acid decomposition activity. The "one or several" in (Ml2) may be, for example, 1 to 67, 1 to 50, 1 to 33, 1 to 16, 1 to 13, 1 to 10, 1 to 6, 1 to 3, 1 or 2, or 1 in the base sequence of (Ml1).

[0214] In the (M13), the "identity" may be within a range such that the protein encoded by the polynucleotide of (M13) does not have inosinic acid decomposition activity. The identity of (M13) to the nucleotide sequence of (M11), for example, is 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0215] In (M14), the "hybridizing polynucleotide" may be any polynucleotide as long as the protein encoded by the polynucleotide of (M14) does not have inosinate decomposition activity. In (M14), the "hybridizing polynucleotide" is, for example, a polynucleotide that is completely or partially complementary to the polynucleotide of (M11). In (M14), the hybridization and stringent conditions can be the same as those described in (Pn4).

[0216] The polynucleotide (M15) may have a nucleotide sequence such that the protein encoded by the polynucleotide (M15) does not have inosinic acid decomposition activity. The nucleotide sequence of the polynucleotide (M15) can be designed, for example, by substituting corresponding codons based on the amino acid sequence of SEQ ID NO: 16.

[0217] Amino acid sequence of mutant medaka NT5E protein (SEQ ID NO: 16): MTLRWRCCALGALLGLLLRLDSWSGASGFELTLLHTNDVHARIEETSEDSSKCHEAGSCFAGVARMFTKDGDPEKGDARAVSGRWRSISRHGVVQLLQRQRSCAFHEQTWL

[0218] In (M16), the "one or several" in the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (M16) does not have inosinic acid decomposition activity. The "one or several" in (M16) may be, for example, 1 to 22, 1 to 16, 1 to 11, 1 to 5, 1 to 4, 1 to 3, 1 or 2, or 1 in the amino acid sequence of SEQ ID NO: 16.

[0219] In the (M17), the "identity" of the amino acid sequence may be within a range in which the protein encoded by the polynucleotide of (M17) does not have inosinate decomposition activity, for example. The identity of (M17) to the amino acid sequence of SEQ ID NO: 16 is, for example, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more.

[0220] In the present disclosure, when the function of the nt5e gene is lost by suppressing the expression of the nt5e gene, the loss of function of the nt5e gene can be achieved, for example, by introducing a polynucleotide that suppresses the expression of the nt5e gene into a target fish. The method for introducing the polynucleotide is not particularly limited and can be, for example, RNA interference, antisense RNA, genome editing, or other methods. An expression cassette such as an expression vector containing the polynucleotide can be introduced into a target fish by, for example, microinjection, polyethylene glycol, electroporation, particle gun, or other methods. The target fish may be, for example, eggs, larvae, fry, immature fish, or adult fish.

[0221] The fish of the present disclosure can suppress a decrease in freshness, for example, compared to fish having a wild-type (normal) nt5e gene. The freshness can be evaluated using the K value. The K value can be calculated using the following formula (1) based on the measured molar amounts (mol) of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosinic acid (IMP), inosine (HxR), and hypoxanthine (Hx) per weight (mg) of the skeletal muscle of the target fish. The molar amounts of ATP, ADP, AMP, IMP, HxR, and Hx per skeletal muscle can be quantified using HPLC in accordance with the method described in Example 3 below. (Calculation formula for K value) K = (HxR + Hx) / (ATP + ADP + AMP + IMP + HxR + Hx) ... (1) K: Index value of freshness ATP: Molar amount of adenosine triphosphate per muscle weight ADP: Molar amount of adenosine diphosphate per muscle weight AMP: Molar amount of adenosine monophosphate per muscle weight IMP: Molar amount of inosinic acid per muscle weight HxR: Molar amount of inosine per muscle weight Hx: Molar amount of hypoxanthine per muscle weight

[0222] For example, when stored at 4°C for two days after death, the fish of the present disclosure have a freshness-maintaining activity or a freshness-deterioration-inhibiting activity that reduces the K value by 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more, based on the K value of fish having a wild-type (normal) nt5e gene that has been stored at 4°C for two days after death. Furthermore, when fish of the present disclosure are stored at 4° C. for two days after death, they have a freshness-maintaining activity or a freshness-decline-inhibiting activity that reduces the K value by 5 to 100%, 5 to 95%, 5 to 90%, 10 to 85%, 10 to 80%, 10 to 75%, 15 to 70%, 15 to 65%, 15 to 60%, 20 to 55%, 20 to 50%, 20 to 45%, 25 to 40%, 25 to 35%, or 25 to 30%, based on the K value of fish having a wild-type (normal) nt5e gene that has been stored at 4° C. for two days after death. Therefore, the fish of the present disclosure can also be referred to as, for example, fish having freshness-maintaining activity or fish having freshness-decline-inhibiting activity.

[0223] As described above, the fish of the present disclosure are obtained by inducing a loss-of-function mutation in the wild-type nt5e gene. Therefore, the fish of the present disclosure can also be referred to as, for example, a "mutant fish." The fish of the present disclosure may also be a descendant line of a "mutant fish" and may be a fish having a loss-of-function mutation in the nt5e gene. The fish of the present disclosure can also be referred to as, for example, a mutant fish having a genetic mutation introduced into the base sequence of the nt5e gene by the above-described method for introducing a mutation. The fish of the present disclosure exclude, for example, fish obtained solely by means of an essentially biological process.

[0224] For the method of producing fish of the present disclosure, the descriptions of the first production method, second production method, screening method, and third production method described below can be used.

[0225] <Fish Portion> In another aspect, the present disclosure provides a fish portion in which accumulation of inosinic acid is enhanced or promoted during aging. The fish portion of the present disclosure is the fish portion of the present disclosure.

[0226] The fish of the present disclosure may be the first fish of the present disclosure described above, or the second fish of the present disclosure described below.

[0227] The fish part may be, for example, an edible part of a fish, such as muscle, reproductive organs (e.g., testes, ovaries), skin, liver, or bone.

[0228] <First Production Method> In another aspect, the present disclosure provides a method for producing the fish of the present disclosure using the fish of the present disclosure, and a method for reproducing the fish of the present disclosure, which includes the following step (a): (a) crossbreeding the fish of the present disclosure with another fish.

[0229] The first production method of the present disclosure uses the fish of the present disclosure in step (a), and therefore can produce fish with accelerated maturation, for example.

[0230] In step (a), the fish used as the first parent may be any of the fish of the present disclosure. As described above, the fish of the present disclosure may be obtained, for example, by the providing method, second production method, screening method, and third production method described below. Therefore, the first production method of the present disclosure may, for example, perform one or more of the providing method, second production method, screening method, and third production method described below prior to step (a). In this case, the description of each method can be referenced below.

[0231] As a specific example, the first production method of the present disclosure may include the following steps (x) and (y): (x) a step of selecting a fish of the present disclosure from a test fish (selection step), and (y) a step of producing a fish of the present disclosure from a target fish (production step).

[0232] In the step (x), the selection of the fish can be said to be the selection of fish in which the nt5e gene has lost its function. Therefore, the step (x) can be carried out, for example, by the following steps (x1) and (x2): (x1) a detection step of detecting whether the nt5e gene of the test fish has lost its function; and (x2) a selection step of selecting the test fish as a fish of the present disclosure if the nt5e gene has lost its function.

[0233] When the step (x) includes the steps (x1) and (x2), the step (x) may be carried out, for example, using the base sequence of the nt5e gene as an index, or may be carried out using the expression level of the nt5e gene or the NT5E protein as an index.

[0234] When the base sequence of the nt5e gene is used as an indicator, in step (x1), the loss of function of the nt5e gene may be detected, for example, by decoding the base sequence of the nt5e gene of the test fish and comparing it with the base sequence of the corresponding wild-type nt5e gene or a loss-of-function form of the nt5e gene. The base sequence can be decoded, for example, using a sequencer. Then, in step (x2), for example, if the base sequence of the nt5e gene of the test fish is a base sequence in which a loss-of-function mutation has been introduced into the base sequence of the wild-type nt5e gene of the corresponding fish, or if it matches the base sequence of the loss-of-function form of the nt5e gene of the corresponding fish, the fish is selected as the fish of the present disclosure. The selection conditions are described below. The base sequence of the wild-type nt5e gene can be determined by referring to the base sequence of the wild-type nt5e gene of each of the aforementioned fish. Furthermore, the base sequence of the loss-of-function nt5e gene can be determined by reference to the base sequences of the loss-of-function nt5e gene of each of the fish species described above. The comparison of base sequences can be performed, for example, using base sequence analysis software (e.g., the aforementioned BLAST). In step (x2), the region for comparison of base sequences may be the intron region of the nt5e gene or the exon region of the nt5e gene, with the latter being preferred. Furthermore, when the loss-of-function of the nt5e gene is caused by introducing a mutation, such as an insertion, deletion, and / or substitution of one or more bases, into the base sequence of the corresponding wild-type nt5e gene, step (x1) may be performed using, for example, a primer set, probe, or a combination thereof capable of detecting at least one mutation. The primer set and probe can be designed, for example, based on the type of mutation, using methods commonly used in the art.

[0235] In step (x2), for example, if one or more bases have been inserted, deleted, and / or substituted with respect to the wild-type nt5e gene, the gene may be determined to be a loss-of-function gene. Furthermore, in step (x2), for example, if a frameshift mutation has been introduced into the wild-type nt5e gene, the gene may be determined to be a loss-of-function gene. Furthermore, in step (x2), for example, if the wild-type nt5e gene is partially or completely deleted, the gene may be determined to be a loss-of-function gene.

[0236] In the step (x2), for example, if the test fish has a loss-of-function form of the nt5e gene in a heterozygous or homozygous form, the test fish may be selected as a fish of the present disclosure.

[0237] When the expression level of the nt5e gene is used as an index, in the step (x1), the detection of the loss of function of the nt5e gene may be carried out, for example, by detecting the function of the mRNA of the nt5e gene or the protein encoded by the nt5e gene in the test fish. Furthermore, in the step (x1), the detection of the loss of function of the nt5e gene may be carried out, for example, by detecting the presence or absence of expression of the nt5e gene or the protein encoded by the nt5e gene in the test fish, or the expression level of the nt5e gene or the protein encoded by the nt5e gene.

[0238] When the step (x) is based on the expression of the protein encoded by the nt5e gene, the step (x1) involves, for example, measuring the expression level of at least one of the nt5e gene and the protein encoded by the nt5e gene in a biological sample from the test fish. Then, in the step (x2), fish that have lost the function of the nt5e gene (fish with loss of function) are selected based on the expression level of at least one of the nt5e gene and the protein encoded by the nt5e gene in the biological sample from the test fish and a reference value. Specifically, in the step (x2), the selection of fish with loss of function among the test fish can be carried out by, for example, comparing the expression level of at least one of the nt5e gene and the protein encoded by the nt5e gene in the biological sample from the test fish with the reference value.

[0239] The biological sample from the test fish is not particularly limited and may be, for example, either an individual fish or a part of an individual fish, and is preferably fish skeletal muscle. The type of biological sample used in step (x1) may be, for example, one type or two or more types.

[0240] In the step (x1), the expression level of the nt5e gene can be measured by, for example, semi-quantitative PCR, quantitative PCR, Northern blotting, digital PCR, RNA sequence analysis (RNAseq), etc. Furthermore, in the step (x1), the expression level of the protein encoded by the nt5e gene can be measured by, for example, a method using a spectrophotometer, such as an ultraviolet absorption method or a bicinchoninic acid method, or a protein quantification method, such as ELISA or Western blotting.

[0241] Examples of the reference value include the expression level of the nt5e gene or the protein encoded by the nt5e gene in the wild-type fish, and the expression level of the nt5e gene or the protein encoded by the nt5e gene in fish having a loss-of-function form of the nt5e gene. When the expression level of the nt5e gene in the loss-of-function fish is used as the reference value, the loss-of-function fish may be, for example, a fish in which one of the two nt5e genes located on each of a pair of chromosomes has lost function, i.e., a heterozygous fish, or a fish in which both genes have lost function, i.e., a homozygous fish. The expression level of the nt5e gene or the protein encoded by the nt5e gene used as the reference value can be obtained, for example, by measuring the expression level of the nt5e gene or the protein encoded by the nt5e gene in a biological sample collected under the same conditions as the biological sample of the test fish, using the same method as for the biological sample of the test fish. The reference value may be measured in advance, or may be measured simultaneously with the biological sample of the test fish, for example.

[0242] In this case, in the step (x2), the method for evaluating whether the nt5e gene in the test fish has lost its function is not particularly limited, and can be determined appropriately depending on the type of the reference value.

[0243] As a specific example, if the expression level of the nt5e gene in the biological sample of the test fish is the same (no significant difference) as the expression level of the nt5e gene in fish that have the wild-type nt5e gene in homozygous form, if the expression level of the nt5e gene in the biological sample of the test fish is (significantly) higher than the expression level of the nt5e gene in fish that have the wild-type nt5e gene in homozygous form, and / or if the expression level of the nt5e gene is (significantly) higher than the expression level of the nt5e gene in a biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as not having loss-of-function of the nt5e gene, for example. On the other hand, if the expression level of the nt5e gene in the biological sample of the test fish is (significantly) lower than the expression level of the nt5e gene in a biological sample of fish having the wild-type nt5e gene in homozygous form, if it is the same as (not significantly different from) the expression level of the nt5e gene in a biological sample of fish having a loss-of-function form of the nt5e gene in homozygous or heterozygous form, and / or if it is (significantly) lower than the expression level of the nt5e gene in a biological sample of fish having a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as having, for example, a loss-of-function of the nt5e gene.

[0244] Furthermore, if the expression level of NT5E protein in the biological sample of the test fish is the same (no significant difference) as the expression level of NT5E protein in fish that have the wild-type NT5E protein in homozygous form, if the expression level of NT5E protein in the biological sample of the test fish is (significantly) higher than the expression level of NT5E protein in fish that have the wild-type NT5E protein in homozygous form, and / or if the expression level of NT5E protein is (significantly) higher than the expression level of NT5E protein in biological samples of fish that have a loss-of-function form of the NT5E protein in homozygous or heterozygous form, the test fish can be evaluated as not having loss-of-function of the NT5E gene, for example. On the other hand, if the expression level of NT5E protein in a biological sample from the test fish is (significantly) lower than the expression level of NT5E protein in a biological sample from fish that have the wild-type NT5E protein in a homozygous form, if it is the same as (not significantly different from) the expression level of NT5E protein in a biological sample from fish that have a loss-of-function form of NT5E protein in a homozygous or heterozygous form, and / or if it is (significantly) lower than the expression level of NT5E protein in a biological sample from fish that have a loss-of-function form of NT5E protein in a homozygous or heterozygous form, the test fish can be evaluated as having, for example, a loss-of-function of the nt5e gene.

[0245] Then, in the step (x2), for example, fish that are evaluated as having a loss of function of the nt5e gene are selected as the fish of the present disclosure.

[0246] In step (x2), for example, the genotype of the nt5e gene may be evaluated based on the expression level of the nt5e gene. Specifically, the genotype may be evaluated as a homozygous type of the normal gene, a heterozygous type of the normal gene and a loss-of-function gene, or a homozygous type of the loss-of-function gene. In this case, the reference value may be a fish having the wild-type nt5e gene in a homozygous type (wild-type fish) or a fish having a loss-of-function form of the nt5e gene in a heterozygous or homozygous type (heterozygous fish or homozygous fish). Specifically, in step (x2), if the expression level of the target gene in the test fish is equivalent to the expression level of the target gene in the wild-type fish, the heterozygous fish, or the homozygous fish, the test fish can be evaluated as having the same genotype as, for example, a fish having an equivalent expression level.

[0247] The step (y) can also be referred to as, for example, a step of causing the function of the nt5e gene of the target fish (a loss-of-function step). The explanation of the loss-of-function step in the imparting method of the present disclosure, which will be described later, can be applied to the loss-of-function step.

[0248] Next, in the step (a), the fish used as the other parent is not particularly limited and can be a fish having any trait. The fish used as the other parent may be the fish disclosed herein.

[0249] In the step (a), the method for crossbreeding the fish of the present disclosure with the other fish is not particularly limited, and any known method can be used. In the step (a), a progeny lineage of fish can be obtained by crossbreeding the fish of the present disclosure with the other fish.

[0250] The first production method of the present disclosure may further include the following step (b): (b) a selection step of selecting fish in which the function of the ecto-5′-nucleotidase (nt5e) gene has been lost from the fish obtained in step (a) or from their progeny lines.

[0251] In step (b), the target for selecting fish in which the nt5e gene has lost its function may be, for example, the fish obtained in step (a), or may be a progeny line obtained from the fish. Specifically, the target may be, for example, an F1 fish obtained by the crossbreeding in step (a), or a progeny line thereof. The progeny line may be, for example, a self-crossed progeny or backcrossed progeny of the F1 fish obtained by the crossbreeding in step (a), or a fish obtained by crossbreeding a progeny line such as the F1 fish with another fish.

[0252] In the step (b), selection of fish in which the function of the nt5e gene has been lost can be carried out, for example, by directly or indirectly confirming the loss of function of the nt5e gene.

[0253] In step (b), the direct confirmation can be determined for the obtained F1 fish or its progeny lineage, for example, based on the amount of inosinic acid in a biological sample. Specifically, the loss of function of the nt5e gene can be evaluated based on the content of inosinic acid in fish flesh one day (24 hours) after death of fish having a wild-type nt5e gene or fish having a loss-of-function form of the nt5e gene. More specifically, the amount of inosinic acid in a biological sample 24 hours after death of the test fish is measured in accordance with Example 1 described below. If the amount of inosinic acid in the biological sample of the test fish is the same as the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form (no significant difference), if it is (significantly) lower than the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form, and / or if it is (significantly) lower than the amount of inosinic acid in the biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as not having loss-of-function of the nt5e gene, for example. On the other hand, if the amount of inosinic acid in the biological sample of the test fish is (significantly) higher than the amount of inosinic acid in the biological sample of fish that have the wild-type nt5e gene in homozygous form, if the amount of inosinic acid is the same as (no significant difference from) the amount of inosinic acid in the biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, and / or if the amount of inosinic acid is (significantly) higher than the amount of inosinic acid in the biological sample of fish that have a loss-of-function form of the nt5e gene in homozygous or heterozygous form, the test fish can be evaluated as having, for example, a loss-of-function of the nt5e gene.

[0254] In the step (b), the selection by indirect confirmation can be carried out, for example, by the following steps (b1) and (b2): (b1) a detection step of detecting whether the nt5e gene of the test fish has lost its function in the step (a); and (b2) a selection step of selecting the test fish as a fish having lost the function of the nt5e gene if the nt5e gene has lost its function.

[0255] The selection of fish in which the nt5e gene has lost its function in step (b) can be carried out, for example, in the same manner as described in step (x), and step (b1) can be carried out in the same manner as step (x1), and step (b2) can be carried out in the same manner as step (x2).

[0256] In the first production method of the present disclosure, it is preferable to further cultivate the fish selected in step (b). The conditions and methods for cultivating the fish can be determined appropriately depending on, for example, the growth stage and variety of the fish. In the cultivation, the fish may be grown to any growth stage, for example.

[0257] Thus, in the step (b), fish in which the function of the nt5e gene has been lost or their progeny lines can be selected.

[0258] The first production method of the present disclosure may further include a collection step of collecting gametes (e.g., eggs, sperm) from the progeny line obtained by crossbreeding.

[0259] <Second Production Method> In another aspect, the present disclosure provides a method for producing fish with accelerated maturation. The production method of the present disclosure is a method for producing fish with accelerated maturation, and includes a function-eliminating step of eliminating the function of the ecto-5'-nucleotidase (nt5e) gene of a target fish. According to the second production method of the present disclosure, fish with accelerated maturation can be obtained. Furthermore, according to the second production method of the present disclosure, for example, the accumulation of inosinic acid during maturation can be promoted. Therefore, the second production method of the present disclosure can also be said to be a method for producing fish with accelerated accumulation of inosinic acid during maturation, for example.

[0260] Furthermore, in the fish of the present disclosure, for example, the decomposition of inosinic acid to inosine and hypoxanthine during aging is suppressed, so that the freshness is maintained when stored for the same period. Therefore, the enhancement method of the present disclosure can also be referred to as, for example, a method for producing fish whose freshness is maintained, a method for producing fish whose loss of freshness is suppressed, a method for maintaining the freshness of fish, or a method for suppressing the loss of freshness of fish.

[0261] In the present disclosure, as described above, the loss of function of the nt5e gene may be achieved by introducing a loss-of-function mutation into the nt5e gene, by introducing a polynucleotide that suppresses the expression of the nt5e gene, or by crossbreeding the target fish with the fish of the present disclosure, i.e., by hybrid introgression of a loss-of-function form of the nt5e gene. When the loss-of-function is achieved by crossbreeding, the imparting method of the present disclosure can be carried out in the same manner as, for example, the first production method of the present disclosure.

[0262] When a loss-of-function mutation is introduced into the nt5e gene, the loss-of-function step involves, for example, introducing a loss-of-function mutation into the nt5e gene of a target fish. The target fish has, for example, the nt5e gene on each of a pair of chromosomes. Therefore, the loss-of-function step may involve, for example, loss of function of the nt5e gene on one of the pair of chromosomes in the target fish, or loss of function of the nt5e genes on both chromosomes, with the latter being preferred.

[0263] The loss of function of the nt5e gene can be achieved, for example, by introducing a mutation as described above. The above explanation can be applied to the mutation, and it is preferably a nonsense mutation or a frameshift mutation. The loss-of-function mutation may be introduced, for example, by deleting, substituting, inserting, and / or adding one or several bases in each gene (the base sequence of each gene), and is preferably introduced by partially or completely deleting the wild-type nt5e gene.

[0264] In the function loss step, the region into which the function loss mutation is introduced into the nt5e gene may be an intron region or an exon region of the nt5e gene, but the latter is preferred.

[0265] The loss of function of the nt5e gene can be induced, for example, by introducing a mutation into the nt5e gene of the target fish using a conventional method. The method for introducing the mutation can be carried out, for example, by homologous recombination; genome editing techniques using ZFN, TALEN, CRISPR-CAS9, CRISPR-CPF1, etc. For a method for introducing a mutation using the genome editing technique, see, for example, Example 1 described below. The method for introducing the mutation may also be carried out, for example, by random mutagenesis. Examples of the random mutagenesis method include irradiation treatment with α-rays, β-rays, γ-rays, X-rays, etc.; chemical treatment with mutagens such as ethyl methanesulfonate (EMS) or ethynylnitrosourea (ENU); heavy ion beam treatment; and the like. The above-mentioned methods for introducing the mutation may also be carried out using, for example, commercially available kits.

[0266] The target fish may be, for example, any of eggs, larvae, fry, juvenile fish, and adult fish.

[0267] In the second production method of the present disclosure, it is preferable to select fish having a loss-of-function mutation introduced into the nt5e gene after the loss-of-function step. The fish to be selected may be, for example, the fish obtained in the loss-of-function step or a progeny lineage thereof. The selection may be carried out, for example, in the same manner as in the above-mentioned step (x), and the description thereof may be used.

[0268] Next, when introducing a polynucleotide that suppresses the expression of the nt5e gene, the method for introducing the polynucleotide is not particularly limited and can be carried out by, for example, RNA interference, antisense RNA, genome editing technology, etc. An expression cassette such as an expression vector containing the polynucleotide can be introduced into the target fish by, for example, microinjection, polyethylene glycol method, electroporation method, particle gun method, etc. The target fish may be, for example, eggs, larvae, fry, juvenile fish, or adult fish.

[0269] <Method for Enhancing Inosinic Acid Content> In another aspect, the present disclosure provides a method for enhancing the inosinic acid content of fish or fish meat during aging. The enhancement method of the present disclosure is a method for enhancing the inosinic acid content of fish meat during aging, comprising an aging step of aging fish or fish meat, wherein the fish meat is a fish of the present disclosure, fish meat of a fish of the present disclosure, and / or edible fish meat of a fish of the present disclosure. According to the enhancement method of the present disclosure, the inosinic acid content in the fish or fish meat can be enhanced during aging. For example, the enhancement method of the present disclosure enhances the increase in inosinic acid during aging compared to fish homozygously possessing the wild-type nt5e gene, thereby enabling the same inosinic acid content to be achieved earlier. Therefore, the enhancement method of the present disclosure can also be referred to as, for example, a method for promoting the aging of fish or fish meat, or a method for promoting the accumulation of inosinic acid in fish or fish meat.

[0270] In the aging step, the fish or fish meat can be aged under general aging conditions for fish or fish meat. Specific examples of the aging temperature include 1 to 10° C. The aging period is, for example, 0.1 to 31 days, 0.5 to 20 days, or 1 to 3 days.

[0271] <Screening Method> In another aspect, the present disclosure provides a method for screening fish with accelerated maturation. The screening method for fish with accelerated maturation of the present disclosure includes a selection step of selecting, from test fish, test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost its function, as fish with accelerated maturation. According to the present disclosure, fish with accelerated maturation can be screened. The screening method of the present invention can also be said to be a method for screening fish with the ability to enhance (promote) the accumulation of inosinic acid, for example.

[0272] Furthermore, the fish of the present disclosure maintains its freshness when stored for the same period of time because, for example, decomposition of inosinic acid to inosine and hypoxanthine during aging is suppressed. Therefore, the screening method of the present disclosure can also be said to be, for example, a screening method for fish whose freshness is maintained or a screening method for fish whose loss of freshness is suppressed.

[0273] In the screening method of the present disclosure, the selection step can be carried out in the same manner as in the step (x), and the explanation therefor can be cited.

[0274] <Third Production Method> In another aspect, the present disclosure provides a method for producing fish with accelerated maturation. The fish production method of the present disclosure includes a screening step of screening test fish for test fish with a loss-of-function of the nt5e gene, and the screening step is carried out by the screening method for fish with accelerated maturation of the present disclosure. According to the third production method of the present disclosure, fish with a loss-of-function of the nt5e gene can be screened, thereby producing fish with accelerated maturation.

[0275] <Second Fish> In another aspect, the present disclosure provides a fish with accelerated aging. The fish of the present disclosure (hereinafter also referred to as the "second fish") is obtained by the first production method, the second production method, or the third production method of the present disclosure. The fish of the present disclosure can provide a fish with accelerated aging. Furthermore, the present disclosure is expected to promote the accumulation of inosinic acid in the fish meat after death, thereby producing fish that is chewy and delicious.

[0276] <Detection Method> In another aspect, the present disclosure provides a method capable of detecting the ability to promote maturation in fish. The detection method of the present disclosure includes a detection step of detecting whether the ecto-5'-nucleotidase (nt5e) gene has lost function in a test fish. The detection method of the present disclosure makes it possible to detect whether maturation is promoted or whether the accumulation of inosinic acid is enhanced during maturation in a test fish. Therefore, the detection method of the present disclosure can also be referred to as, for example, a method for screening fish having the ability to promote maturation, or a method for screening fish having the ability to enhance (promote) the accumulation of inosinic acid.

[0277] The detection method of the present disclosure includes, for example, a detection step of detecting a loss-of-function mutation in the nt5e gene of a test fish. The detection step can be performed using, for example, the explanation of step (x) in the selection step of the first production method of the present disclosure or the indirect selection. Specifically, the detection step detects gene expression or the base sequence of the nt5e gene.

[0278] The detection method of the present disclosure preferably further includes a determination step of determining whether the nt5e gene of the test fish is a wild-type nt5e gene or a loss-of-function nt5e gene based on the gene expression or base sequence. The determination step can be performed, for example, by comparing the nt5e gene of the test fish with the wild-type nt5e gene of the corresponding fish. Specifically, in the determination step, the nt5e gene of the test fish can be determined to be a wild-type nt5e gene if it has the same base sequence as the wild-type nt5e gene of the corresponding fish, if it has a mutation that is not a loss-of-function mutation, or if it does not match the base sequence of the loss-of-function nt5e gene of the corresponding fish. On the other hand, in the determination process, if the nt5e gene of the test fish has a loss-of-function mutation in the wild-type nt5e gene of the corresponding fish, or if it matches the base sequence of a loss-of-function form of the nt5e gene of the corresponding fish, the nt5e gene of the test fish can be determined to be a loss-of-function form of the nt5e gene.

[0279] <Processed Food> In another aspect, the present disclosure provides a processed food using the fish of the present disclosure. The processed fish food of the present disclosure uses the fish of the present disclosure.

[0280] The processed fish food of the present disclosure may use either the first fish of the present disclosure or the second fish of the present disclosure as the fish to be processed.

[0281] In the processed foods of the present disclosure, "processing" is not particularly limited and means, for example, any treatment of fish. Specific examples of the processing include cutting, slicing, mincing, straining, drying, canning, bottling, washing, packaging, freezing, heating, seasoning, etc. The processing carried out in the production of the processed food may be one type or multiple types. Furthermore, in the production of the processed food, the same treatment may be carried out once or multiple times.

[0282] The present disclosure will be described in detail below using examples, but the present disclosure is not limited to the aspects described in the examples.

[0283] [Example 1] Medaka fish lacking the function of the nt5e gene were produced, and it was confirmed that the accumulation of inosinic acid was enhanced in each case compared to wild-type medaka fish, i.e., that the nt5e gene encodes an enzyme that degrades inosinic acid.

[0284] (1) Preparation of fertilized eggs Sexually mature medaka fish were placed in the same tank and separated into males and females using a partition or other device from the evening before microinjection. On the day of microinjection, the partition was removed and natural mating was allowed to occur to obtain one-cell stage fertilized eggs. The collected eggs were used for microinjection after removing any threads adhering to the egg membrane using tweezers or other tools.

[0285] (2) Creation of loss-of-function medaka Mutations were introduced using CRISPR-Cas9, with reference to Reference 1 below. Cas9 was a protein reagent purchased from Integrated DNA Technologies, Inc. Reference 1: Satoshi Ansai et.al, "Targeted mutagenesis using CRISPR / Cas system in medaka", Biology Open, 2014, vol.3, pages 362-371

[0286] Single guide RNAs (sgRNAs) were synthesized using a vector-free, cloning-free method. Template DNA for synthesis was prepared by PCR using three oligonucleotides (OligoA-gRNA1 or OligoA-sgRNA2, OligoB, and OligoC). sgRNA1 and sgRNA2 were synthesized using template DNA and a kit (CUGA® 7 gRNA Synthesis Kit, Nippon Gene Co., Ltd.), and then purified using an RNA purification kit (RNeasy Plus Mini Kit, Qiagen). The sgRNA's target site on the genome is the following target sequence located in exon 1 or exon 9 of the ecto-5'-nucleotidase (nt5e) gene. There are 10 types of nt5 genes in the medaka genome database. Among these, the nt5e gene, classified as an extracellular type, has generally been reported to have a high affinity for inosinic acid (see Reference 2). Medaka fish have two nt5e genes, but synteny analysis revealed that the nt5e gene (ENSORLG00000014932) on chromosome 22 is conserved across a wide range of fish species. In the target sequence below, the three underlined bases at the 3' end are the protospacer adjacent motif (PAM) sequence. Reference 2: H. Zimmermann, "5'-Nucleotidase: molecular structure and functional aspects," Biochem J. 1992 Jul 15;285 (Pt 2)(Pt 2):345-65.

[0287] (OligoA-sgRNA1) 5'-CTAATACGACTCACTATAGCAGGATGTTCACCAAAGTGAGTTTTAGAGCTAGAAATAGCA-3' (SEQ ID NO: 17)

[0288] (OligoA-sgRNA2) 5'-CTAATACGACTCACTATAGGTGATGCGGCCTTCCACTGCGTTTTAGAGCTAGAAATAGCA-3' (SEQ ID NO: 18)

[0289] (OligoB) 5'-AAAAGCACCGACTCGGTGCCACTTTTTCAAGTTGATAACGGACTAGCCTTATTTTAACTTGCTATTTCTAGCTCTAAAAC-3' (SEQ ID NO: 19)

[0290] (OligoC) 5'-AAAAGCACCGACTCGGTGCC-3' (SEQ ID NO: 20)

[0291] (Target sequence on exon 1: sgRNA1) 5'-CAGGATGTTCACCAAAGTGACGG-3' (SEQ ID NO: 21)

[0292] (Target sequence on exon 9: sgRNA2) 5'-GTGATGCGGCCTTCCACTGCAGG-3' (SEQ ID NO: 22)

[0293] The cytoplasm of the one-cell stage fertilized eggs obtained in (1) was introduced by microinjection with 500 ng / μL Cas9 protein and 100 ng / μL sgRNA1, and a mutation was introduced into the nt5e gene (Case 1). Furthermore, the cytoplasm of the one-cell stage fertilized eggs obtained in (1) was introduced by microinjection with 500 ng / μL Cas9 protein, 100 ng / μL sgRNA1, and 100 ng / μL sgRNA2, and a mutation was introduced into the nt5e gene (Case 2). The mutated medaka was then mated with a wild-type medaka to obtain second-generation medaka. DNA extracted from the caudal fin of the second-generation medaka was analyzed, and individuals with base deletions in the nt5e gene were selected by PCR and base sequence analysis. The individuals were crossed to obtain individuals into which a loss-of-function mutation in the nt5e gene had been introduced. Among the individuals into which a loss-of-function mutation in the nt5e gene had been introduced, Case 1 was a 2-base deletion line (Δ2). Furthermore, among the individuals into which a loss-of-function mutation in the nt5e gene had been introduced, Case 2 was a 5521-base deletion line (Δ5521).

[0294] The fertilized eggs were cultured and hatched, and then reared using standard aquaculture methods. Three months after hatching, each individual was immediately sacrificed and stored at 4°C for 2 or 4 days for aging. After storage, skeletal muscle was collected from each individual and its weight was measured. After measurement, 10% perchloric acid was added and homogenized. After homogenization, the homogenized material was centrifuged at 12,900 rpm (or 15,000 x g) for 10 minutes. After centrifugation, a supernatant fraction was obtained. After collection, the supernatant fraction was neutralized with 1N KOH and then centrifuged at 12,900 rpm (or 15,000 x g) for 10 minutes. After centrifugation, a supernatant fraction was obtained. The supernatant fraction was then adjusted to volume with distilled water, and the amount of inosinic acid per skeletal muscle weight (nmol / mg skeletal muscle) was measured using HPLC. In the measurement, a C18 reverse phase column (4.6 mm ID x 250 mm, OTD-80Ts, manufactured by Tosoh Corporation) was used. The results are shown in Tables 2 and 3 below and in FIG. 1.

[0295]

[0296]

[0297] FIG. 1 is a graph showing the amount of inosinic acid in medaka with loss of function of the nt5e gene. In FIG. 1, (A) shows the amount of inosinic acid in medaka after two days of aging, and (B) shows the amount of inosinic acid in medaka after four days of aging. In FIG. 1, the horizontal axis indicates the type of individual, and the vertical axis indicates the amount of inosinic acid. As shown in FIG. 1(A) and Table 2, after two days of aging, the amount of inosinic acid was significantly higher in both the heterozygous knockout and homozygous knockout of medaka Δ2 in Case 1, and in both the heterozygous knockout and homozygous knockout of medaka Δ5521 in Case 2, compared to the control medaka (wild-type medaka). 1(B) and Table 3, after 4 days of aging, the amount of inosinic acid was significantly higher in both the heterozygous and homozygous knockouts of medaka Δ2 in Case 1, and the heterozygous knockout of medaka Δ5521 in Case 2, compared to the control medaka (wild-type medaka). From the above, it was found that the amount of inosinic acid was enhanced in the medaka of the present disclosure after 2 and 4 days of aging, compared to wild-type medaka, that is, the introduction of a loss-of-function mutation into the nt5e gene suppressed the decomposition activity of inosinic acid.

[0298] Example 2 Red sea bream lacking the function of the nt5e gene was produced, and it was confirmed that the activity of decomposing inosinic acid was suppressed compared to that of wild-type red sea bream.

[0299] Instead of male and female medaka, male and female red sea bream were used, and mutations were introduced into the nt5e gene in the same manner, except that the sgRNA was changed. The target site on the genome of the sgRNA in red sea bream is the following target sequence present in exon 6 of the Pm-nt5e gene. In the target sequence below, the three underlined bases at the 3' end are the protospacer adjacent motif (PAM) sequence.

[0300] (Target sequence on exon 6: Pm-Nt5-sgRNA) 5'-TCAGGAGGTGGGAAAGACTCTGG-3' (SEQ ID NO: 23)

[0301] Next, the same procedure as in Example 1 was used, except that the fertilized eggs of the red sea bream introduced as above were used. Each individual was immediately sacrificed six months after hatching, and the amount of inosinic acid was measured over time at 1, 2, 3, 5, and 7 days after death. Specifically, skeletal muscle was collected from each individual and the weight of the skeletal muscle was measured. After the measurement, 10% perchloric acid was added and the sample was homogenized. After the homogenization, the sample was centrifuged at 12,900 rpm (or 15,000 g) for 10 minutes. After the centrifugation, the supernatant fraction was collected. After the collection, the supernatant fraction was neutralized with 1N KOH and then centrifuged at 12,900 rpm (or 15,000 g) for 10 minutes. After the centrifugation, the supernatant fraction was collected. The supernatant fraction was then adjusted to volume with distilled water, and the amount of inosinic acid was measured using HPLC. In the measurement, a C18 reverse phase column (4.6 mm ID x 250 mm, OTD-80Ts, manufactured by Tosoh Corporation) was used. The results are shown in Figure 2.

[0302] FIG. 2 is a graph showing the amount of inosinic acid in red seabream with a loss of function of the nt5e gene. In FIG. 2, the horizontal axis represents the number of days since death (aging period), and the vertical axis represents the amount of inosinic acid. As shown in FIG. 2, the red seabream of Example 2 (mutation group) had a higher amount of inosinic acid at all time points compared to the control red seabream (wild-type red seabream, control group). From these results, it was found that the red seabream of the present disclosure has a suppressed inosinic acid degradation activity compared to wild-type red seabream. Note that the red seabream of Example 2 was obtained using a chimeric individual, but it is clear that the inosinic acid degradation activity is suppressed. Therefore, it is presumed that by converting the red seabream into an individual with a heterozygous or homozygous loss-of-function form of the nt5e gene, the accumulation of inosinic acid will be enhanced, as with the medaka of Example 1.

[0303] [Example 3] Tilapia lacking the function of the nt5e gene were produced, and it was confirmed that the activity of decomposing inosinic acid was suppressed and freshness was maintained compared to wild-type tilapia.

[0304] Instead of male and female medaka, male and female tilapia were used, and mutations were introduced into the nt5e gene in the same manner, except for the sgRNA. The target site of the sgRNA in the tilapia genome is the following target sequence (nucleotide sequence 217 to 239 in the nucleotide sequence of SEQ ID NO: 5) present in exon 1 of the nt5e gene. In the target sequence below, the three underlined bases at the 5' end are the protospacer adjacent motif (PAM) sequence.

[0305] (Target sequence on exon 1: sgRNA-t) 5'-CCCTGCTTCGCTGGTGTGGCCAG-3' (SEQ ID NO: 24)

[0306] Next, in the same manner as in Example 1, except that the fertilized eggs of the introduced tilapia were used, each individual was immediately sacrificed 50 days after hatching and stored at 4°C for aging for 2 or 4 days. After storage, the amount of nucleic acids (ATP, ADP, AMP, IMP, HxR, Hx) of each individual was measured. Specifically, skeletal muscle was collected from each individual and weighed. After measurement, 10% perchloric acid was added and homogenized. After homogenization, centrifugation was performed at 12,900 rpm (or 15,000 x g) for 10 minutes. After centrifugation, the supernatant fraction was collected. After collection, the supernatant fraction was neutralized with 1N KOH and then centrifuged at 12,900 rpm (or 15,000 x g) for 10 minutes. After centrifugation, the supernatant fraction was collected. The supernatant fraction was then adjusted to volume with distilled water, and the amount of nucleic acid was measured using HPLC. The K value, an index of freshness, was calculated using the nucleic acid measurement value and the following formula (1). The following formula was used for the calculation. A C18 reverse-phase column (4.6 mm ID × 250 mm, OTD-80Ts, manufactured by Tosoh Corporation) was used in the measurement. The results are shown in Figure 3. (Calculation formula for K value) K = (HxR + Hx) / (ATP + ADP + AMP + IMP + HxR + Hx) ... (1) K: Index value of freshness ATP: Molar amount of adenosine triphosphate per muscle weight ADP: Molar amount of adenosine diphosphate per muscle weight AMP: Molar amount of adenosine monophosphate per muscle weight IMP: Molar amount of inosinic acid per muscle weight HxR: Molar amount of inosine per muscle weight Hx: Molar amount of hypoxanthine per muscle weight

[0307] FIG. 3 is a graph showing the amount of inosinic acid and K value of tilapia with loss of function of the nt5e gene. In FIG. 3, (A) shows the amount of inosinic acid in tilapia after two days of aging, and (B) shows the K value of tilapia after four days of aging. In FIG. 3(A), the horizontal axis indicates the type of individual, and the vertical axis indicates the amount of inosinic acid. In FIG. 3(B), the horizontal axis indicates the type of individual, and the vertical axis indicates the K value. As shown in FIG. 3(A), after two days of aging, the amount of inosinic acid in the tilapia of Example 3 (GE) was 34% higher than that of the control tilapia (wild-type tilapia, WT). Furthermore, as shown in FIG. 3(B), after four days of aging, the K value in the tilapia of Example 3 (GE) was 28% lower than that of the control tilapia (wild-type tilapia, WT). From the above, it was found that the tilapia of the present disclosure has suppressed inosinic acid decomposition activity after 2 days of aging and maintains freshness after 4 days, compared to wild-type tilapia.

[0308] From the above, it was found that the fish of the present disclosure have suppressed inosinic acid decomposition activity and maintain freshness compared to wild-type fish. [Example 4] Flounder with loss of function of the nt5e gene were produced, and it was confirmed that the inosinic acid decomposition activity was suppressed and freshness was maintained compared to wild-type flounder.

[0309] Instead of male and female medaka, male and female flounder were used, and mutations were introduced into the nt5e gene in the same manner, except for the sgRNA. The target site on the genome of the flounder sgRNA is the following target sequence (605-627 base sequence in the base sequence of SEQ ID NO: 11) present in exon 4 of the nt5e gene. In the target sequence below, the three underlined bases on the 3' end are the protospacer adjacent motif (PAM) sequence.

[0310] (Target sequence on exon 4: sgRNA-p) 5'-CTTCAACGGAGGCGGCGTCCGGG-3' (SEQ ID NO: 27)

[0311] Next, in the same manner as in Example 1, except that the fertilized eggs of the introduced flounder were used, each individual was immediately killed 546 days after fertilization and stored at 4°C for 2 days for maturation. After the storage, the amounts of nucleic acids (ATP, ADP, AMP, IMP, HxR, Hx) of each individual were measured. Specifically, this was carried out in the same manner as in Example 2. The results are shown in Figure 4.

[0312] FIG. 4 is a graph showing the amount of inosinic acid and K value of flounder with loss of function of the nt5e gene. In FIG. 4, (A) shows the amount of inosinic acid in flounder after two days of aging, and (B) shows the K value of flounder after two days of aging. In FIG. 4(A), the horizontal axis shows the type of individual, and the vertical axis shows the amount of inosinic acid. In FIG. 4(B), the horizontal axis shows the type of individual, and the vertical axis shows the K value. As shown in FIG. 4(A), after two days of aging, the flounder of Example 4 (GE) had an 8% higher amount of inosinic acid than the control flounder (wild-type flounder, WT). Furthermore, as shown in FIG. 4(B), after two days of aging, the flounder of Example 4 (GE) had a 37% lower K value than the control flounder (wild-type flounder, WT). From the above, it was found that the flounder of the present disclosure has suppressed flounder acid decomposition activity after two days of aging and maintains freshness compared to wild-type flounder.

[0313] From the above, it was found that the fish of the present disclosure have suppressed inosinic acid decomposition activity and maintain freshness compared to wild-type fish.

[0314] Although the present disclosure has been described above with reference to the embodiments and examples, the present disclosure is not limited to the above-described embodiments and examples. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure.

[0315] The patents, patent applications, and publications cited herein are incorporated by reference into this specification in their entirety as if the contents were specifically set forth herein.

[0316] This application claims priority based on Japanese Patent Application No. 2022-096417, filed on June 15, 2022, the disclosure of which is incorporated herein in its entirety.

[0317] <Appendix> Some or all of the above embodiments and examples can be described as in the following appendices, but are not limited to the following. <Fish> (Appendix 1) A fish that has lost the function of the ecto-5'-nucleotidase (nt5e) gene. (Appendix 2) The fish according to Appendix 1, comprising a loss-of-function form of the nt5e gene, wherein the loss-of-function form is a mutant gene in which one or several bases have been deleted, substituted, inserted, and / or added in the base sequence of the normal nt5e gene. (Appendix 3) The fish according to Appendix 2, wherein the loss-of-function form is a mutant gene in which at least some bases have been deleted in the base sequence of the normal nt5e gene. (Appendix 4) The fish according to any of Appendices 1 to 3, comprising a loss-of-function form of the nt5e gene, wherein the loss-of-function form is a mutant gene containing a frameshift mutation in the base sequence of the normal nt5e gene. (Appendix 5) The fish according to any one of Appendices 1 to 4, comprising a loss-of-function form of the nt5e gene, wherein the loss-of-function form is a mutant gene containing a nonsense mutation relative to the base sequence of the normal nt5e gene. (Appendix 6) The fish according to any one of Appendices 1 to 5, comprising a loss-of-function form of the nt5e gene, wherein the loss-of-function form is a gene containing a mutation in the first exon of the normal nt5e gene. (Appendix 7) The fish according to any one of Appendices 2 to 6, wherein the fish is red sea bream (Pagrus major), and the normal nt5e gene of the red sea bream is a gene comprising the polynucleotide of (Pn) below: (Pn) Any of the polynucleotides of (Pn1) to (Pn7) below: (Pn1) A polynucleotide consisting of the base sequence of SEQ ID NO: 1; (Pn2) A polynucleotide consisting of an amino acid sequence in which inosinic acid is deleted, substituted, inserted and / or added in the base sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn7) A polynucleotide consisting of an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 2, and encoding a protein having inosinic acid decomposition activity.(Appendix 8) The fish according to any of Appendices 2 to 7, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in at least one of exon 1 and exon 6 of a normal nt5e gene. (Appendix 9) The fish according to Appendices 8, wherein the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 6 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene. (Appendix 10) The fish according to any of Appendices 2 to 9, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in bases 1014 to 1036 in the nucleotide sequence of SEQ ID NO: 1.(Appendix 11) The fish according to any one of Appendices 2 to 6, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the normal nt5e gene of the tiger pufferfish is a gene comprising the polynucleotide of (Pt) below: (Pt) Any of the polynucleotides of (Pt1) to (Pt7) below: (Pt1) A polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 3; (Pt2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt3) A polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt5) A polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide comprising an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 4, and encoding a protein having inosinic acid decomposition activity; (Pt7) A polynucleotide comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 4, and encoding a protein having inosinic acid decomposition activity. (Appendix 12) The fish according to any of Appendices 2 to 6 and 11, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish comprises a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function form of the nt5e gene. (Appendix 13) The pufferfish is a fish according to Appendix 12, which has a mutation in exon 1 of the normal nt5e gene as a loss-of-function form of the nt5e gene, and comprises a mutant gene having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene.(Appendix 14) The fish according to any one of Appendices 2 to 6 and 11 to 13, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish has a mutation at bases 131 to 153 in the base sequence of SEQ ID NO: 3 as a loss-of-function form of the nt5e gene. (Appendix 15) The fish according to any one of Appendices 2 to 6, wherein the fish is a tilapia (Oreochromis niloticus), and the normal nt5e gene of the tilapia is a gene comprising the polynucleotide of (Po) below: (Po) Any of the polynucleotides of (Po1) to (Po7) below: (Po1) A polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 5; (Po2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po3) A polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po5) A polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide comprising an amino acid sequence in which one or several amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6, and encoding a protein having inosinic acid decomposition activity; (Po7) A polynucleotide comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 6, and encoding a protein having inosinic acid decomposition activity. (Appendix 16) The fish according to any of Appendices 2 to 6 and 15, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function form of the nt5e gene.(Appendix 17) The fish according to Appendices 16, wherein the tilapia has a mutation in exon 1 of the normal nt5e gene as a loss-of-function form of the nt5e gene, and comprises a mutant gene having a frameshift mutation or a nonsense mutation with respect to the base sequence of the normal nt5e gene. (Appendix 18) The fish according to any of Appendices 2 to 6 and 15 to 17, wherein the fish is a tilapia (Oreochromis niloticus), and has a mutation in bases 217 to 239 in the base sequence of SEQ ID NO: 5 as a loss-of-function form of the nt5e gene. (Appendix 19) The fish according to any one of Appendices 2 to 6, wherein the fish is a flounder (Paralichthys olivaceus), and the normal nt5e gene of the flounder is a gene comprising the polynucleotide of (Pp) below: (Pp) any one of the polynucleotides of (Pp1) to (Pp7) below: (Pp1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 11; (Pp2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp3) a polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp4) A polynucleotide that consists of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of (Pp1), and that encodes a protein having inosinic acid decomposition activity; (Pp5) A polynucleotide that encodes a protein having the amino acid sequence of SEQ ID NO: 12; (Pp6) A polynucleotide that consists of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 12, and that encodes a protein having inosinic acid decomposition activity; (Pp7) A polynucleotide that consists of an amino acid sequence that is 90% or more identical to the amino acid sequence of SEQ ID NO: 12, and that encodes a protein having inosinic acid decomposition activity.(Appendix 20) The fish according to any of Appendices 2 to 6 and 19, wherein the fish is a flounder (Paralichthys olivaceus), and the flounder comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 4 of a normal nt5e gene. (Appendix 21) The fish according to Appendices 20, wherein the flounder comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 4 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene. (Appendix 22) The fish according to any of Appendices 2 to 6 and 19 to 21, wherein the fish is a flounder (Paralichthys olivaceus), and the flounder comprises, as a loss-of-function form of the nt5e gene, a mutation in bases 605 to 627 in the nucleotide sequence of SEQ ID NO: 11.(Appendix 23) The fish according to any one of Appendices 2 to 6, wherein the fish is a catfish (Clarias garienpinus), and the normal nt5e gene of the catfish is a gene comprising the polynucleotide of (Pq) below: (Pq) Any of the polynucleotides of (Pq1) to (Pq7) below: (Pq1) A polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 25; (Pq2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq3) A polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide comprising the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq5) A polynucleotide encoding a protein comprising the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 26; (Pq7) A polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence having 90% or more identity to the amino acid sequence of SEQ ID NO: 26. (Appendix 24) The fish according to any of Appendices 2 to 6, 8 to 10, 12 to 14, 16 to 18, and 20 to 22, wherein the loss-of-function entity encodes a mutant NT5E protein with reduced inosinic acid decomposition activity. (Appendix 25) The fish according to any one of Appendices 1 to 6, wherein the fish is a fish selected from the group consisting of Tetraodontidae, Sparidae, Salmonidae, Cyprinidae, Grouperidae, Pleuronectidae, Catfishidae, and Cichlidae. <Part of fish> (Appendix 26) A part of a fish according to any one of Appendices 1 to 25. (Appendix 27) A part of a fish according to Appendices 26, wherein the part is an edible part.<Method for producing fish> (Appendix 28) A method for producing fish, comprising the following step (a): (a) a breeding step of crossbreeding a fish according to any one of Appendices 1 to 25 with another fish. (Appendix 29) A production method according to Appendix 28, comprising the following step (b): (b) a selection step of selecting fish having lost the function of the ecto-5'-nucleotidase (nt5e) gene from the fish obtained from the step (a) or from its progeny line. (Appendix 30) A production method according to Appendix 28 or 29, comprising the following step (x) prior to the step (a): (x) a step of selecting a fish according to any one of Appendices 1 to 25 from target fish. (Appendix 31) A production method according to Appendix 30, wherein the selection in the step (x) is selection of a fish having a lost-function form of the ecto-5'-nucleotidase (nt5e) gene. (Appendix 32) The production method according to Appendix 28 or 29, comprising the following step (y) prior to the step (a): (y) a production step of producing a fish according to any one of Appendices 1 to 25 from a target fish. <Production method of fish with accelerated maturation> (Appendix 33) A production method of fish with accelerated maturation, comprising a function-loss step of causing the ecto-5'-nucleotidase (nt5e) gene of the target fish to lose its function. (Appendix 34) The production method according to Appendix 33, in which the function-loss step involves introducing a loss-of-function mutation into the nt5e gene of the target fish to produce fish containing a loss-of-function form of the nt5e gene. (Appendix 35) The production method according to Appendix 34, in which the loss-of-function form is a mutant gene in which one or several bases have been deleted, substituted, inserted and / or added in the base sequence of a normal nt5e gene. (Appendix 36) The production method according to Appendices 35, wherein the loss-of-function form is a mutant gene in which at least some bases are deleted in the base sequence of the normal nt5e gene. (Appendix 37) The production method according to any of Appendices 34 to 36, wherein the loss-of-function form is a mutant gene containing a frameshift mutation in the base sequence of the normal nt5e gene. (Appendix 38) The production method according to any of Appendices 34 to 37, wherein the loss-of-function form is a mutant gene containing a nonsense mutation in the base sequence of the normal nt5e gene.(Appendix 39) The production method according to any one of Appendices 34 to 38, wherein the loss-of-function form is a mutant gene containing a mutation in the first exon of a normal nt5e gene. (Appendix 40) The method according to any one of Appendices 34 to 39, wherein the fish is red sea bream (Pagrus major), and the normal nt5e gene of the red sea bream is a gene comprising the polynucleotide of (Pn) below: (Pn) any one of the polynucleotides (Pn1) to (Pn7) below: (Pn1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 1; (Pn2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide consisting of the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2; (Pn6) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2 in which one or several amino acids have been deleted, substituted, inserted, and / or added, and having inosinic acid degrading activity; (Pn7) A polynucleotide encoding a protein consisting of an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 2, and having inosinic acid degrading activity. (Appendix 41) The production method according to any of Appendices 34 to 40, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 6 of the normal nt5e gene. (Appendix 42) The production method according to Appendices 41, wherein the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 6 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene.(Appendix 43) The production method according to any one of Appendices 34 to 42, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises a mutant gene having mutations at bases 1014 to 1036 in the base sequence of SEQ ID NO: 1 as a loss-of-function form of the nt5e gene. (Appendix 44) The method according to any one of Appendices 34 to 39, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the normal nt5e gene of the tiger pufferfish is a gene comprising the polynucleotide of (Pt) below: (Pt) any one of the polynucleotides (Pt1) to (Pt7) below: (Pt1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 3; (Pt2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt4) A polynucleotide which comprises a nucleotide sequence complementary to a polynucleotide which hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pt1), and which encodes a protein having inosinic acid decomposition activity; (Pt5) A polynucleotide which encodes a protein having the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide which comprises an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 4, and which encodes a protein having inosinic acid decomposition activity; (Pt7) A polynucleotide which comprises an amino acid sequence which is 80% or more identical to the amino acid sequence of SEQ ID NO: 4, and which encodes a protein having inosinic acid decomposition activity. (Appendix 45) The method of any of Appendices 34 to 39 and 44, wherein the fish is pufferfish (Takifugu rubripes), and the pufferfish comprises a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function form of the nt5e gene.(Appendix 46) The production method according to Appendices 45, wherein the tiger pufferfish has a mutation in exon 1 of the normal nt5e gene as a loss-of-function form of the nt5e gene and comprises a mutant gene having a frameshift mutation or a nonsense mutation with respect to the base sequence of the normal nt5e gene. (Appendix 47) The production method according to any of Appendices 34 to 39 and 44 to 46, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish has a mutation in bases 131 to 153 of the base sequence of SEQ ID NO: 3 as a loss-of-function form of the nt5e gene. (Appendix 43) The method according to any one of Appendices 34 to 39, wherein the fish is tilapia (Oreochromis niloticus), and the normal nt5e gene of the tilapia is a gene comprising the polynucleotide of (Po) below: (Po) Any of the polynucleotides of (Po1) to (Po7) below: (Po1) A polynucleotide consisting of any of the nucleotide sequences of SEQ ID NO: 5; (Po2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po3) A polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po4) A polynucleotide that has a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of (Po1), and that encodes a protein having inosinic acid decomposition activity; (Po5) A polynucleotide that encodes a protein having the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide that has an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6, and that encodes a protein having inosinic acid decomposition activity; (Po7) A polynucleotide that has an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 6, and that encodes a protein having inosinic acid decomposition activity.(Appendix 49) The production method according to any one of Appendices 34 to 39 and 48, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of a normal nt5e gene. (Appendix 50) The production method according to Appendices 49, wherein the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene. (Appendix 51) The fish according to any one of Appendices 34 to 39 and 48 to 50, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutation in bases 217 to 239 in the nucleotide sequence of SEQ ID NO: 5.(Appendix 52) The fish according to any of Appendices 34 to 39, wherein the fish is a flounder (Paralichthys olivaceus), and the normal nt5e gene of the flounder is a gene comprising the polynucleotide of (Pp) below: (Pp) any of the polynucleotides of (Pp1) to (Pp7) below: (Pp1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 11; (Pp2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp3) a polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp4) a polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp5) a polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 12; (Pp6) a polynucleotide comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 12, and encoding a protein having inosinic acid decomposition activity; (Pp7) a polynucleotide comprising an amino acid sequence having 90% or more identity to the amino acid sequence of SEQ ID NO: 12, and encoding a protein having inosinic acid decomposition activity. (Appendix 53) The fish according to any one of Appendices 34 to 39 and 52, wherein the fish is a flounder (Paralichthys olivaceus), and the flounder comprises a mutant gene having a mutation in exon 4 of a normal gene for nt5e, as a loss-of-function form of the nt5e gene. (Appendix 54) The flounder is a fish according to Appendix 53, wherein the flounder is a loss-of-function form of the nt5e gene, has a mutation in exon 4 of the normal nt5e gene, and includes a mutant gene having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene.(Appendix 55) The fish according to any one of Appendices 34 to 39 and 52 to 54, wherein the fish is a flounder (Paralichthys olivaceus), and the flounder has a mutation at bases 605 to 627 in the base sequence of SEQ ID NO: 11 as a loss-of-function form of the nt5e gene. (Appendix 56) The fish according to any one of claims 34 to 39, wherein the fish is a catfish (Clarias garienpinus), and the normal nt5e gene of the catfish is a gene comprising the polynucleotide of (Pq) below: (Pq) any of the polynucleotides of (Pq1) to (Pq7) below: (Pq1) a polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 25; (Pq2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq3) a polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq4) A polynucleotide encoding a protein having inosinate decomposition activity, comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide consisting of the nucleotide sequence of (Pq1); (Pq5) A polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide encoding a protein having inosinate decomposition activity, comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 26; (Pq7) A polynucleotide encoding a protein having inosinate decomposition activity, comprising an amino acid sequence having 90% or more identity to the amino acid sequence of SEQ ID NO: 26. (Appendix 57) The method of any of Appendices 24 to 29, 41 to 43, 45 to 47, 49 to 51, and 53 to 55, wherein the loss-of-function form encodes a mutant NT5E protein with reduced inosinate decomposition activity.(Appendix 58) The production method according to any of Appendices 34 to 57, wherein the creation step comprises: an introduction step of introducing a mutation into the nt5e gene of a target fish; and a selection step of selecting, from the target fish into which the mutation has been introduced, fish containing a loss-of-function form of the nt5e gene, as fish in which maturation has been accelerated. <Method for enhancing inosinic acid content during maturation of fish meat> (Appendix 59) A method for enhancing inosinic acid content during maturation of fish meat, comprising an ageing step of maturing fish meat, wherein the fish meat is meat of a fish according to any of Appendices 1 to 25 and / or edible meat of a fish according to Appendices 26 or 27. (Appendix 60) The enhancement method according to Appendices 59, wherein the maturation period of the fish meat in the ageing step is 1 to 31 days. <Method for screening fish with accelerated maturation> (Appendix 61) A method for screening fish with accelerated maturation, comprising a selection step of selecting, from test fish, test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost its function, as fish with accelerated maturation. (Appendix 62) The screening method according to Appendix 61, wherein, in the selection step, test fish containing a loss-of-function form of the nt5e gene are selected as fish with accelerated maturation, and the loss-of-function form is a mutant gene in which one or several bases have been deleted, substituted, inserted, and / or added in the base sequence of the normal nt5e gene. (Appendix 63) The screening method according to Appendix 62, wherein the loss-of-function form is a mutant gene in which at least some bases have been deleted in the base sequence of the normal nt5e gene. (Appendix 64) The screening method according to any one of Appendices 62 to 63, wherein in the selection step, test fish containing a loss-of-function form of the nt5e gene are selected as fish with accelerated maturation, and the loss-of-function form is a mutant gene with a frameshift mutation in the base sequence of the normal nt5e gene. (Appendix 65) The screening method according to any one of Appendices 62 to 64, wherein in the selection step, test fish containing a loss-of-function form of the nt5e gene are selected as fish with accelerated maturation, and the loss-of-function form is a mutant gene with a nonsense mutation in the base sequence of the normal nt5e gene.(Appendix 66) A screening method described in any of Appendices 62 to 65, wherein in the selection step, test fish containing a loss-of-function form of the nt5e gene are selected as fish with accelerated maturation, and the loss-of-function form is a mutant gene containing a mutation in the first exon of the normal nt5e gene. (Appendix 67) The screening method according to any one of Appendices 62 to 66, wherein the fish is red sea bream (Pagrus major), and the normal nt5e gene of the red sea bream is a gene comprising the polynucleotide of the following (Pn): (Pn) any one of the polynucleotides (Pn1) to (Pn7) below: (Pn1) a polynucleotide consisting of any of the nucleotide sequences of SEQ ID NO: 1; (Pn2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide consisting of the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2; (Pn6) A polynucleotide encoding a protein consisting of an amino acid sequence in which one or several amino acids are deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 2, and having inosinic acid decomposition activity; (Pn7) A polynucleotide encoding a protein consisting of an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 2, and having inosinic acid decomposition activity. (Appendix 68) The screening method according to any of Appendices 62 to 67, wherein the fish is red sea bream (Pagrus major), and the red sea bream contains a mutant gene having a mutation in exon 6 of a normal nt5e gene as a loss-of-function form of the nt5e gene.(Appendix 69) The screening method according to Appendices 68, wherein the red seabream comprises, as a loss-of-function form of the nt5e gene, a mutant gene that has a mutation in exon 6 of the normal nt5e gene and that has a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene. (Appendix 70) The screening method according to any of Appendices 62 to 69, wherein the fish is red seabream (Pagrus major), and the red seabream comprises, as a loss-of-function form of the nt5e gene, a mutant gene that has a mutation in bases 1014 to 1036 in the nucleotide sequence of SEQ ID NO: 1. (Appendix 71) The screening method according to any one of Appendices 62 to 66, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the normal nt5e gene of the tiger pufferfish is a gene comprising the polynucleotide of (Pt) below: (Pt) any one of the polynucleotides (Pt1) to (Pt7) below: (Pt1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 3; (Pt2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt4) A polynucleotide that has a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of (Pt1), and that encodes a protein having inosinic acid decomposition activity; (Pt5) A polynucleotide that encodes a protein having the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide that has an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 4, and that encodes a protein having inosinic acid decomposition activity; (Pt7) A polynucleotide that has an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 4, and that encodes a protein having inosinic acid decomposition activity.(Appendix 72) The screening method according to any one of Appendices 62 to 66 and 71, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of a normal nt5e gene. (Appendix 73) The screening method according to Appendices 72, wherein the tiger pufferfish comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene. (Appendix 74) The screening method according to any one of Appendices 62 to 66 and 71 to 73, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish comprises, as a loss-of-function form of the nt5e gene, a mutation in bases 131 to 153 of the nucleotide sequence of SEQ ID NO: 3.(Appendix 75) The screening method according to any one of Appendices 62 to 66, wherein the fish is tilapia (Oreochromis niloticus), and the normal nt5e gene of the tilapia is a gene comprising the polynucleotide of (Po) below: (Po) any one of the polynucleotides of (Po1) to (Po7) below: (Po1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 5; (Po2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po5) A polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6, and encoding a protein having inosinic acid decomposition activity; (Po7) A polynucleotide comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 6, and encoding a protein having inosinic acid decomposition activity. (Appendix 76) The screening method according to any of Appendices 62 to 66 and 75, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function form of the nt5e gene. (Appendix 77) The screening method according to Appendix 76, wherein the tilapia contains a mutant gene that has a mutation in exon 1 of the normal nt5e gene as a loss-of-function form of the nt5e gene and has a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene.(Appendix 78) The screening method according to any one of Appendices 62 to 66 and 75 to 77, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia has a mutation at bases 217 to 239 in the base sequence of SEQ ID NO: 5 as a loss-of-function mutant of the nt5e gene. (Appendix 79) The screening method according to any one of Appendices 62 to 66, wherein the fish is a flounder (Paralichthys olivaceus), and the normal nt5e gene of the flounder is a gene comprising the polynucleotide of (Pp) below: (Pp) any one of the polynucleotides of (Pp1) to (Pp7) below: (Pp1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 11; (Pp2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp4) a polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp5) a polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 12; (Pp6) a polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 12; (Pp7) a polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 12. (Appendix 80) The screening method according to any of Appendices 62 to 66 and 79, wherein the fish is olive flounder (Paralichthys olivaceus), and the olive flounder comprises a mutant gene having a mutation in exon 4 of a normal nt5e gene as a loss-of-function form of the nt5e gene.(Appendix 81) The screening method according to Appendices 80 to 82, wherein the flounder has a mutation in exon 4 of the normal nt5e gene as a loss-of-function form of the nt5e gene and comprises a mutant gene having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene. (Appendix 82) The screening method according to any of Appendices 62 to 66 and 79 to 81, wherein the fish is olive flounder (Paralichthys olivaceus), and the flounder has a mutation in bases 605 to 627 of the base sequence of SEQ ID NO: 11 as a loss-of-function form of the nt5e gene. (Appendix 83) The screening method according to any one of Appendices 62 to 66, wherein the fish is a catfish (Clarias garienpinus), and the normal nt5e gene of the catfish is a gene comprising the polynucleotide of (Pq) below: (Pq) Any of the polynucleotides of (Pq1) to (Pq7) below: (Pq1) A polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 25; (Pq2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq3) A polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq4) A polynucleotide that consists of a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of (Pq1), and that encodes a protein having inosinic acid decomposition activity; (Pq5) A polynucleotide that encodes a protein having the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide that consists of an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 26, and that encodes a protein having inosinic acid decomposition activity; (Pq7) A polynucleotide that consists of an amino acid sequence that is 90% or more identical to the amino acid sequence of SEQ ID NO: 26, and that encodes a protein having inosinic acid decomposition activity.<Method for producing fish> (Appendix 84) A method for producing fish, comprising a screening step of screening test fish for test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost its function, wherein the screening step is carried out by the screening method described in any of Appendices 62 to 78. <Fish> (Appendix 85) Fish obtained by the production method described in any of Appendices 28 to 58 and 84. <Detection method> (Appendix 86) A method for detecting the ability to promote maturation in fish, comprising a detection step of detecting whether the ecto-5'-nucleotidase (nt5e) gene has lost its function in the test fish. (Appendix 87) The detection method described in Appendix 86, wherein the detection step includes a detection step of detecting whether a loss-of-function form of the nt5e gene is present in the test fish. (Appendix 88) The detection method according to Appendix 87, wherein the loss-of-function entity is a mutant gene in which one or several bases are deleted, substituted, inserted and / or added in the base sequence of a normal nt5e gene. (Appendix 89) The detection method according to Appendix 88, wherein the loss-of-function entity is a mutant gene in which at least some bases are deleted in the base sequence of the normal nt5e gene. (Appendix 90) The detection method according to any of Appendices 87 to 89, wherein the loss-of-function entity is a mutant gene containing a frameshift mutation in the base sequence of the normal nt5e gene. (Appendix 91) The detection method according to any of Appendices 87 to 90, wherein the loss-of-function entity is a mutant gene containing a nonsense mutation in the base sequence of the normal nt5e gene. (Appendix 92) The detection method according to any of Appendices 87 to 91, wherein the loss-of-function entity is a mutant gene containing a mutation in the first exon of the normal nt5e gene.(Appendix 93) The detection method according to any one of Appendices 87 to 92, wherein the fish is red sea bream (Pagrus major), and the normal nt5e gene of the red sea bream is a gene comprising the polynucleotide of the following (Pn): (Pn) any one of the polynucleotides (Pn1) to (Pn7) below: (Pn1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 1; (Pn2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn4) a polynucleotide consisting of a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide consisting of the nucleotide sequence of (Pn1), and encoding a protein having inosinic acid decomposition activity; (Pn5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2; (Pn6) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 2 in which one or several amino acids have been deleted, substituted, inserted, and / or added, and having inosinic acid degrading activity; (Pn7) A polynucleotide encoding a protein consisting of an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 2, and having inosinic acid degrading activity. (Appendix 94) The detection method according to any of Appendices 87 to 93, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 6 of the normal nt5e gene. (Appendix 95) The detection method according to Appendices 94, wherein the red sea bream comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 6 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the nucleotide sequence of the normal nt5e gene.(Appendix 96) The detection method according to any one of Appendices 87 to 95, wherein the fish is red sea bream (Pagrus major), and the red sea bream comprises a mutant gene having mutations at bases 1014 to 1036 in the base sequence of SEQ ID NO: 1 as a loss-of-function form of the nt5e gene. (Appendix 97) The detection method according to any one of Appendices 87 to 92, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the normal nt5e gene of the tiger pufferfish is a gene comprising the polynucleotide of (Pt) below: (Pt) any one of the polynucleotides (Pt1) to (Pt7) below: (Pt1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 3; (Pt2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pt1), and encoding a protein having inosinic acid decomposition activity; (Pt5) A polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted, and / or added in the amino acid sequence of SEQ ID NO: 4, and encoding a protein having inosinic acid decomposition activity; (Pt7) A polynucleotide comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 4, and encoding a protein having inosinic acid decomposition activity. (Appendix 98) The detection method according to any of Appendices 87 to 92 and 97, wherein the fish is a pufferfish (Takifugu rubripes), and the pufferfish comprises a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function form of the nt5e gene.(Appendix 99) The detection method according to Appendices 98, wherein the tiger pufferfish has a mutation in exon 1 of the normal nt5e gene as a loss-of-function form of the nt5e gene, and comprises a mutant gene having a frameshift mutation or a nonsense mutation with respect to the base sequence of the normal nt5e gene. (Appendix 100) The detection method according to any of Appendices 87 to 92 and 97 to 99, wherein the fish is a tiger pufferfish (Takifugu rubripes), and the tiger pufferfish has a mutation in bases 131 to 153 of the base sequence of SEQ ID NO: 3 as a loss-of-function form of the nt5e gene. (Appendix 101) The detection method according to any one of Appendices 87 to 92, wherein the fish is tilapia (Oreochromis niloticus), and the normal nt5e gene of the tilapia is a gene comprising the polynucleotide of (Po) below: (Po) Any of the polynucleotides of (Po1) to (Po7) below: (Po1) A polynucleotide consisting of any of the nucleotide sequences of SEQ ID NO: 5; (Po2) A polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po3) A polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Po1), and encoding a protein having inosinic acid decomposition activity; (Po4) A polynucleotide that has a base sequence complementary to a polynucleotide that hybridizes under stringent conditions to a polynucleotide consisting of the base sequence of (Po1), and that encodes a protein having inosinic acid decomposition activity; (Po5) A polynucleotide that encodes a protein having the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide that has an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted and / or added in the amino acid sequence of SEQ ID NO: 6, and that encodes a protein having inosinic acid decomposition activity; (Po7) A polynucleotide that has an amino acid sequence that is 80% or more identical to the amino acid sequence of SEQ ID NO: 6, and that encodes a protein having inosinic acid decomposition activity.(Appendix 102) The detection method according to any one of Appendices 87 to 92 and 101, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of a normal nt5e gene. (Appendix 103) The detection method according to Appendices 102, wherein the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutant gene having a mutation in exon 1 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation with respect to the base sequence of the normal nt5e gene. (Appendix 104) The detection method according to any one of Appendices 87 to 92 and 101 to 103, wherein the fish is tilapia (Oreochromis niloticus), and the tilapia comprises, as a loss-of-function form of the nt5e gene, a mutation in bases 217 to 239 in the base sequence of SEQ ID NO: 5.(Appendix 105) The detection method according to any one of Appendices 87 to 92, wherein the fish is a flounder (Paralichthys olivaceus), and the normal nt5e gene of the flounder is a gene comprising the polynucleotide of (Pp) below: (Pp) any one of the polynucleotides of (Pp1) to (Pp7) below: (Pp1) a polynucleotide consisting of any one of the nucleotide sequences of SEQ ID NO: 11; (Pp2) a polynucleotide consisting of a nucleotide sequence in which one or several nucleotides have been deleted, substituted, inserted and / or added in the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp3) a polynucleotide consisting of a nucleotide sequence having 80% or more identity to the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp4) a polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pp1), and encoding a protein having inosinic acid decomposition activity; (Pp5) a polynucleotide encoding a protein having the amino acid sequence of SEQ ID NO: 12; (Pp6) a polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted, and / or added in the amino acid sequence of SEQ ID NO: 12; (Pp7) a polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence having 80% or more identity to the amino acid sequence of SEQ ID NO: 12. (Appendix 106) The detection method according to any of Appendices 87 to 92 and 105, wherein the fish is olive flounder (Paralichthys olivaceus), and the olive flounder contains a mutant gene having a mutation in exon 4 of a normal nt5e gene as a loss-of-function form of the nt5e gene. (Appendix 107) The detection method according to Appendix 106, wherein the flounder contains a mutant gene that has a mutation in exon 4 of the normal nt5e gene as a loss-of-function form of the nt5e gene and has a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene.(Appendix 108) The detection method according to any one of Appendices 87 to 92 and 105 to 107, wherein the fish is a flounder (Paralichthys olivaceus), and the flounder has a mutation at bases 605 to 627 in the base sequence of SEQ ID NO: 11 as a loss-of-function form of the nt5e gene. (Appendix 109) The detection method according to any one of Appendices 87 to 92, wherein the fish is a catfish (Clarias garienpinus), and the normal nt5e gene of the catfish is a gene comprising the polynucleotide of (Pq) below: (Pq) Any of the polynucleotides of (Pq1) to (Pq7) below: (Pq1) A polynucleotide consisting of the nucleotide sequence of SEQ ID NO: 25; (Pq2) A polynucleotide consisting of the nucleotide sequence of (Pq1) in which one or several nucleotides have been deleted, substituted, inserted and / or added, and encoding a protein having inosinic acid decomposition activity; (Pq3) A polynucleotide consisting of a nucleotide sequence having 90% or more identity to the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq4) A polynucleotide comprising a nucleotide sequence complementary to a polynucleotide that hybridizes under stringent conditions to the polynucleotide comprising the nucleotide sequence of (Pq1), and encoding a protein having inosinic acid decomposition activity; (Pq5) A polynucleotide encoding a protein comprising the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence in which one or more amino acids have been deleted, substituted, inserted, and / or added in the amino acid sequence of SEQ ID NO: 26; (Pq7) A polynucleotide encoding a protein having inosinic acid decomposition activity, comprising an amino acid sequence having 90% or more identity to the amino acid sequence of SEQ ID NO: 26. (Appendix 110) The detection method according to any of Appendices 87 to 92, 94 to 96, 98 to 100, 102 to 104, and 106 to 108, wherein the loss-of-function form encodes a mutant NT5E protein with reduced inosinic acid decomposition activity. <Processed Food> (Appendix 111) A processed fish food using the fish according to any one of Appendices 1 to 25 and 85.

[0318] As described above, the fish of the present disclosure can undergo accelerated maturation. Therefore, the present invention is extremely useful in, for example, the fields of fish breeding and fisheries.

Claims

1. Fish with a loss-of-function mutation in the ecto5'-nucleotidase (nt5e) gene.

2. Includes loss-of-function nt5e gene, The fish according to claim 1, wherein the loss-of-function organism is a mutant gene in which 1 to 117 bases are deleted, substituted, inserted and / or added to the base sequence of a normal nt5e gene.

3. The fish according to claim 2, wherein the loss-of-function organism is a mutant gene in which at least some bases are deleted from the base sequence of the normal nt5e gene.

4. Includes loss-of-function nt5e gene, The fish according to any one of claims 1 to 3, wherein the loss-of-function organism is a mutant gene containing a frameshift mutation relative to the base sequence of a normal nt5e gene.

5. Includes loss-of-function nt5e gene, The fish according to any one of claims 1 to 3, wherein the loss-of-function organism is a mutant gene containing a nonsense mutation relative to the base sequence of a normal nt5e gene.

6. Includes loss-of-function nt5e gene, The fish according to any one of claims 1 to 3, wherein the loss-of-function organism is a gene containing a mutation in the first exon of a normal nt5e gene.

7. The aforementioned fish is a red sea bream (Pagrus major), The normal nt5e gene of the aforementioned red sea bream is a gene containing the following (Pn) polynucleotide, according to claim 2 or 3: (Pn) One of the following polynucleotides (Pn1) to (Pn7): (Pn1) A polynucleotide consisting of the base sequence of Sequence ID No. 1; (Pn2) A polynucleotide comprising a base sequence in which 1 to 175 bases are deleted, substituted, inserted and / or added to the base sequence of (Pn1), and which encodes a protein having inosinic acid degradation activity; (Pn3) A polynucleotide comprising a base sequence having 90% or more identity with the base sequence of (Pn1), encoding a protein having inosinic acid degradation activity; (Pn4) A polynucleotide having a complementary base sequence to a polynucleotide that hybridizes under stringent conditions with the base sequence of (Pn1), and encoding a protein having inosinic acid degradation activity; (Pn5) A polynucleotide encoding a protein consisting of the amino acid sequence of Sequence ID No. 2; (Pn6) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence in which 1 to 58 amino acids are deleted, substituted, inserted, and / or added in the amino acid sequence of Sequence ID No. 2; (Pn7) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence that is 90% or more identical to the amino acid sequence of Sequence ID No.

2.

8. The aforementioned fish is a red sea bream (Pagrus major), The fish according to claim 2 or 3, wherein the red sea bream includes a mutant gene having a mutation in at least one of exon 1 and exon 6 of a normal nt5e gene as a loss-of-function body of the nt5e gene.

9. The fish according to claim 8, wherein the red sea bream includes a mutant gene having a mutation in exon 6 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene, as a loss-of-function form of the nt5e gene.

10. The aforementioned fish is a red sea bream (Pagrus major), The fish according to claim 2 or 3, wherein the red sea bream contains a mutant gene having a mutation at bases 1014 to 1036 in the base sequence of Sequence ID No. 1 as a loss-of-function product of the nt5e gene.

11. The aforementioned fish is a tiger pufferfish (Takifugu rubripes), The normal nt5e gene of the aforementioned pufferfish is a gene containing the following polynucleotide (Pt), according to claim 2 or 3: (Pt) Any of the following polynucleotides (Pt1) to (Pt7): (Pt1) A polynucleotide consisting of the base sequence of Sequence ID No. 3; (Pt2) A polynucleotide comprising a base sequence in which 1 to 174 bases are deleted, substituted, inserted and / or added in the base sequence of (Pt1), and which encodes a protein having inosinic acid degradation activity; (Pt3) A polynucleotide comprising a base sequence having 90% or more identity with the base sequence of (Pt1), which encodes a protein having inosinic acid degradation activity; (Pt4) A polynucleotide having a complementary base sequence to a polynucleotide that hybridizes under stringent conditions with the base sequence of (Pt1), and encoding a protein having inosinic acid degradation activity; (Pt5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 4; (Pt6) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence in which 1 to 57 amino acids are deleted, substituted, inserted, and / or added in the amino acid sequence of Sequence ID No. 4; (Pt7) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence that is 90% or more identical to the amino acid sequence of Sequence ID No.

4.

12. The aforementioned fish is a tiger pufferfish (Takifugu rubripes), The fish according to claim 2 or 3, wherein the tiger pufferfish includes a mutant gene having a mutation in exon 1 of a normal nt5e gene as a loss-of-function body of the nt5e gene.

13. The fish according to claim 12, wherein the tiger pufferfish includes a mutant gene having a mutation in exon 1 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene, as a loss-of-function form of the nt5e gene.

14. The aforementioned fish is a tiger pufferfish (Takifugu rubripes), The fish according to claim 2 or 3, wherein the tiger pufferfish has a mutation in the base sequence of Sequence ID No. 3, specifically between the 131st and 153rd bases, as a loss-of-function organism of the nt5e gene.

15. The aforementioned fish is tilapia (Oreochromis niloticus), The normal nt5e gene of the tilapia is a gene comprising the following polynucleotide (Po), according to claim 2 or 3: (Po) Any of the following polynucleotides (Po1) to (Po7): (Po1) A polynucleotide consisting of the base sequence of Sequence ID No. 5; (Po2) A polynucleotide comprising a base sequence in which 1 to 175 bases are deleted, substituted, inserted and / or added in the base sequence of (Po1), and which encodes a protein having inosinic acid degradation activity; (Po3) A polynucleotide comprising a base sequence having 90% or more identity with the base sequence of (Po1), encoding a protein having inosinic acid degradation activity; (Po4) A polynucleotide having a complementary base sequence to a polynucleotide that hybridizes under stringent conditions with the base sequence of (Po1), and encoding a protein having inosinic acid degradation activity; (Po5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 6; (Po6) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence in which 1 to 58 amino acids are deleted, substituted, inserted, and / or added in the amino acid sequence of Sequence ID No. 6; (Po7) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence that is 90% or more identical to the amino acid sequence of Sequence ID No.

6.

16. The aforementioned fish is tilapia (Oreochromis niloticus), The fish according to claim 2 or 3, wherein the tilapia includes a mutant gene having a mutation in exon 1 of the normal nt5e gene as a loss-of-function body of the nt5e gene.

17. The tilapia is a fish according to claim 16, wherein the tilapia includes a mutant gene having a mutation in exon 1 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene, as a loss-of-function form of the nt5e gene.

18. The aforementioned fish is tilapia (Oreochromis niloticus), The fish according to claim 2 or 3, wherein the tilapia has a mutation in the base sequence of Sequence ID No. 5, specifically between the 217th and 239th bases, as a loss-of-function organism of the nt5e gene.

19. The aforementioned fish is a flounder (Paralichthys olivaceus), The normal nt5e gene of the flounder is a gene containing the following polynucleotide (Pp), according to claim 2 or 3: (Pp) Any of the following polynucleotides (Pp1) to (Pp7): (Pp1) A polynucleotide consisting of the base sequence of Sequence ID No. 11; (Pp2) A polynucleotide comprising a base sequence in which 1 to 117 bases are deleted, substituted, inserted and / or added in the base sequence of (Pp1), and which encodes a protein having inosinic acid degradation activity; (Pp3) A polynucleotide comprising a base sequence having 90% or more identity with the base sequence of (Pp1), which encodes a protein having inosinic acid degradation activity; (Pp4) A polynucleotide having a complementary base sequence to a polynucleotide that hybridizes under stringent conditions with the polynucleotide consisting of the base sequence of (Pp1), and encoding a protein having inosinic acid degradation activity; (Pp5) A polynucleotide encoding a protein consisting of the amino acid sequence of Sequence ID No. 12; (Pp6) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence in which 1 to 39 amino acids are deleted, substituted, inserted, and / or added in the amino acid sequence of Sequence ID No. 12; (Pp7) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence that is 90% or more identical to the amino acid sequence of Sequence ID No.

12.

20. The aforementioned fish is a flounder (Paralichthys olivaceus), The fish according to claim 2 or 3, wherein the flounder includes a mutant gene having a mutation in exon 4 of the normal nt5e gene as a loss-of-function form of the nt5e gene.

21. The fish according to claim 20, wherein the flounder includes a mutant gene having a mutation in exon 4 of the normal nt5e gene and having a frameshift mutation or a nonsense mutation relative to the base sequence of the normal nt5e gene, as a loss-of-function form of the nt5e gene.

22. The aforementioned fish is a flounder (Paralichthys olivaceus), The fish according to claim 2 or 3, wherein the flounder has a mutation in the base sequence of Sequence ID No. 11, specifically between the 605th and 627th bases, as a loss-of-function organism of the nt5e gene.

23. The aforementioned fish is a fin catfish (Clarias garienpinus), The normal nt5e gene of the aforementioned fin catfish is a gene containing the following polynucleotide (Pq), according to claim 2 or 3: (Pq) Any of the following polynucleotides (Pq1) to (Pq7): (Pq1) A polynucleotide consisting of the base sequence of Sequence ID No. 25; (Pq2) A polynucleotide comprising a base sequence in which 1 to 185 bases are deleted, substituted, inserted and / or added in the base sequence of (Pq1), and which encodes a protein having inosinic acid degradation activity; (Pq3) A polynucleotide comprising a base sequence having 90% or more identity with the base sequence of (Pq1) above, which encodes a protein having inosinic acid degradation activity; (Pq4) A polynucleotide having a complementary base sequence to a polynucleotide that hybridizes under stringent conditions with the polynucleotide consisting of the base sequence of (Pq1), and encoding a protein having inosinic acid degradation activity; (Pq5) A polynucleotide encoding a protein consisting of the amino acid sequence of SEQ ID NO: 26; (Pq6) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence in which 1 to 61 amino acids are deleted, substituted, inserted, and / or added in the amino acid sequence of SEQ ID NO: 26; (Pq7) A polynucleotide encoding a protein having inosinic acid degradation activity, consisting of an amino acid sequence that is 90% or more identical to the amino acid sequence of Sequence ID No.

26.

24. The fish according to claim 2 or 3, wherein the loss-of-function organism encodes a mutant NT5E protein in which the inosinic acid degradation activity is reduced.

25. The fish according to any one of claims 1 to 3, wherein the fish is selected from the group consisting of the families Tetraodontidae, Sparidae, Salmonidae, Cyprinidae, Serranidae, Pleuronectidae, Dipteroideidae, and Cichlidae.

26. A part of a fish according to any one of claims 1 to 3.

27. A method for producing fish, including the following step (a): (a) A mating step of mating a fish described in any one of claims 1 to 3 with another fish.

28. A method for producing fish with accelerated maturation, A production method comprising a loss-of-function step that causes the ecto-5'-nucleotidase (nt5e) gene of a target fish to lose its function.

29. A method for increasing the inosinic acid content in the maturation of fish meat, This process includes a maturation process for the fish meat. A method for enhancing fish, wherein the fish meat is the fish meat of a fish according to any one of claims 1 to 3, and / or the fish meat of a part of a fish according to claim 26.

30. A screening method for fish with accelerated maturation, comprising a selection step of selecting fish from a group of test fish in which the ecto-5'-nucleotidase (nt5e) gene has lost function, as fish with accelerated maturation.

31. The process includes a screening step to screen for fish in which the ecto-5'-nucleotidase (nt5e) gene has lost function. The screening step is carried out by the screening method described in claim 30, wherein the method for producing fish is as described in claim 30.

32. A method for detecting the maturation-promoting ability of fish, comprising a detection step for detecting whether the ecto-5'-nucleotidase (nt5e) gene is loss of function in the test fish.

33. A processed fish product using the fish described in any one of claims 1 to 3.