Feed for eel larvae, eel production method and eel juvenile form abnormality inhibitor

Abstract

The invention relates to an eel fry feed containing nucleic acids. It is preferable that the content of the nucleic acids is 0.25 wt% or more based on the total dry matter weight of the feed for the eel fry. The feed for the eel fry comprises a yeast extract, and the yeast extract can contain the nucleic acid.

Description

Technical Field

[0001] This invention relates to feed for eel fry, eel production methods, and inhibitors of morphological abnormalities in eel juveniles.

[0002] This application is filed and claims priority based on Japanese Patent Application No. 2023-092243, filed in Japan on June 5, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Currently, glass eels (white eels) are mainly used as breeding stock for eel farming, and wild glass eels are caught and farmed.

[0004] However, the catch of natural glass eels has declined sharply. In order to reduce the impact on natural eels and achieve stable eel farming production, it is necessary to develop artificial production technology for glass eels.

[0005] In 2002, at the fisheries research / education institution (formerly the Fisheries Research Centre) to which the inventors belonged, they successfully bred glass eels artificially for the first time in the world. This research process was extremely difficult, requiring more than 40 years of research to achieve.

[0006] The natural growth environment and ecology of eel larvae are almost unknown, so developing feed that can support the growth of eel larvae requires a lot of continuous exploration. In particular, the process of metamorphosing from egg-hatched larvae (willow eel) into juveniles (glass eel) is the most difficult hurdle.

[0007] Shark egg powder was proposed as an initial feed for eel larvae (Patent Document 1), but despite numerous attempts, no other feed has been found that is both feeding-inducing and growth-promoting for eel larvae. Moreover, even with the aforementioned shark eggs, it is still impossible to achieve the growth / metamorphosis of the willow eel into a glass eel.

[0008] However, by using a diet consisting of shark eggs combined with krill decomposed products and / or soybean peptides treated with phytic acid reduction, metamorphosis into glass eels was first confirmed (Patent Document 2). Thus, shark eggs (especially oil shark eggs) became the main material for eel larvae feed.

[0009] However, with feed made from natural resources, it is difficult to supply in large quantities and stably. Due to the depletion of resources, there is concern about the continued stable supply of oil shark eggs in the future.

[0010] Therefore, the developed feed is a feed for eel larvae containing milk protein and egg yolk powder (Patent Document 3). By feeding eel larvae with this feed, they can metamorphose into glass eels, and it is expected to become a stable feed that can replace the previous oil shark egg feed.

[0011] Existing technical documents

[0012] Patent documents

[0013] Patent document 1: Japanese Patent Application Publication No. 11-253111.

[0014] Patent Document 2: Japanese Patent Application Publication No. 2005-13116.

[0015] Patent document 3: Japanese Patent Application Publication No. 2018-153147. Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] Eels exhibit a very unique growth process. Figure 1 This diagram illustrates the growth process of eels from fertilized eggs to glass eels. After hatching from fertilized eggs, the larvae undergo a pre-leaf eel stage, developing into what is known as the willow leaf eel. The willow leaf eel is transparent and has a distinctive shape resembling a willow leaf. Then, the willow leaf eel metamorphoses into the glass eel (eel fry).

[0018] However, in the case of feeding with milk protein as shown in Patent Document 3, about half of the individuals exhibited morphological abnormalities during the metamorphosis from eel larvae to glass eels (eel juveniles).

[0019] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a feed for eel larvae that can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels by feeding them.

[0020] In addition, the present invention aims to provide a method for producing eels that can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels.

[0021] In addition, the present invention aims to provide an inhibitor of morphological abnormalities in eel juveniles that can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels.

[0022] Methods for solving problems

[0023] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by feeding eel fry with feed containing nucleic acids, the frequency of the occurrence of individuals exhibiting morphological abnormalities could be reduced, thus completing the present invention.

[0024] That is, one aspect of the present invention includes the following scheme.

[0025] (1) A feed for eel larvae, wherein the feed for eel larvae contains nucleic acids.

[0026] (2) The eel fry feed as described in (1) above, wherein the content of the nucleic acid is 0.25% by weight or more relative to the total dry weight of the eel fry feed.

[0027] (3) The eel fry feed as described in (1) or (2) above, wherein the content of the nucleic acid is less than 10% by weight relative to the total dry weight of the eel fry feed.

[0028] (4) The eel fry feed as described in any one of (1) to (3) above, wherein the nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, salts of nucleosides, salts of nucleotides, and salts of polynucleotides.

[0029] (5) The eel fry feed as described in any one of (1) to (4) above, wherein,

[0030] The nucleic acids described have a structure in which bases are bonded to sugars.

[0031] The bases include at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

[0032] (6) The eel fry feed as described in any one of (1) to (5) above, wherein,

[0033] The nucleic acids described have a structure in which bases are bonded to sugars.

[0034] The bases include purine bases and pyrimidine bases.

[0035] (7) The eel fry feed as described in any one of (1) to (6) above, wherein the eel fry feed contains a yeast extract containing the nucleic acid class.

[0036] (8) The eel fry feed as described in any one of (1) to (7) above, wherein the eel fry feed does not contain shark egg components.

[0037] (9) The eel fry feed as described in any one of (1) to (8) above, wherein the eel fry feed further comprises milk protein.

[0038] (10) The eel fry feed as described in any one of (1) to (9) above, wherein the eel fry feed further comprises an egg component.

[0039] (11) A method for producing eel, wherein the method for producing eel includes feeding eel larvae with any one of the eel larvae feeds described in (1) to (10) above.

[0040] (12) The eel production method as described in (11) above, wherein the feeding is satiated feeding.

[0041] (13) The eel production method as described in (11) or (12) above, wherein the eel production method produces artificial seedlings.

[0042] (14) An inhibitor of abnormal morphology in eel juveniles, wherein the inhibitor of abnormal morphology in eel juveniles contains nucleic acids as an active ingredient.

[0043] In addition, the present invention can have the following solutions.

[0044] (15) The morphological abnormality inhibitor of eel juveniles as described in (14) above, wherein the nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, salts of nucleosides, salts of nucleotides, and salts of polynucleotides.

[0045] (16) An inhibitor of abnormal morphology in eel juveniles as described in (14) or (15) above, wherein,

[0046] The nucleic acids described have a structure in which bases are bonded to sugars.

[0047] The bases include at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

[0048] (17) The eel juvenile morphological abnormality inhibitor as described in any one of (14) to (16) above, wherein,

[0049] The nucleic acids described have a structure in which bases are bonded to sugars.

[0050] The bases include purine bases and pyrimidine bases.

[0051] (18) The eel juvenile morphological abnormality inhibitor as described in any one of (14) to (17) above, wherein the eel juvenile morphological abnormality inhibitor comprises a yeast extract containing the nucleic acid class.

[0052] The effects of the invention

[0053] According to the present invention, a feed for eel larvae can be provided that reduces the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels by feeding them.

[0054] In addition, according to the present invention, a method for producing eels can be provided that reduces the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels by feeding them with the eel larvae feed.

[0055] In addition, according to the present invention, an inhibitor of morphological abnormalities in eel juveniles can be provided, which can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels. Attached Figure Description

[0056] Figure 1 This diagram illustrates the growth process of eels up to the glass eel stage.

[0057] Figure 2 This is an image representing an example of a glass eel that was determined to have "no morphological abnormality" or "existing morphological abnormality" in the embodiments.

[0058] Figure 3 This is a graph representing the frequency of morphological abnormalities in each test area of ​​Experiment 1.

[0059] Figure 4 This is a graph showing the frequency of morphological abnormalities in each test area of ​​Experiment 2.

[0060] Figure 5 This is a graph showing the relationship between the nucleic acid content of the feed shown in Experiment 3 and the average total length and average body height of 20-day-old eel larvae. Detailed Implementation

[0061] The following describes the implementation of the eel larvae feed, eel production method, and eel juvenile morphological abnormality inhibitor of the present invention.

[0062] Feed for fry eels

[0063] The eel fry feed of the embodiment contains nucleic acids. By feeding eel fry with the eel fry feed of the embodiment containing nucleic acids, the eel fry can grow into glass eels (eel juveniles), and the frequency of individuals exhibiting morphological abnormalities can be reduced.

[0064] In this specification, "eel larvae" refers to eels in the state before they complete metamorphosis into glass eels. Examples of eel larvae include eels that undergo metamorphosis into early-stage willow eels, willow eels, and glass eels.

[0065] In this specification, "eel juvenile" refers to an eel that has completed metamorphosis into a glass eel, for example, an eel with a pre-anal length / total length ratio of less than 40% and a body height / total length ratio of less than 7%. The glass eel is an example of an eel juvenile.

[0066] For example, by comparing the frequency of individuals exhibiting morphological abnormalities during metamorphosis in a group fed with eel larvae as a control and a group fed with eel larvae of the embodiment, it can be confirmed that the frequency of individuals exhibiting morphological abnormalities is reduced.

[0067] The species of eel used as the feed for eel fry in the feeding method can be any species of eel, such as Japanese eel (Anguilla japonica), European eel (Anguilla anguilla), American eel (Anguilla rostrata), etc., with Japanese eel being preferred.

[0068] In this specification, "nucleic acid class" is a concept that includes nucleosides, nucleotides, polynucleotides, their salts and analogs, decomposition products and fragments.

[0069] Nucleosides have a structure in which the base is bonded to the sugar.

[0070] Examples of such bases include adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

[0071] For the bases mentioned, nucleic acid bases are preferred.

[0072] Examples of sugars include ribose or deoxyribose. Nucleosides can be ribonucleotides where the sugar is ribose or deoxyribonucleotides where the sugar is deoxyribose.

[0073] Specific nucleosides include, for example, adenosine, guanosine, 5-methyluridine, uridine, cytidine, inosine, deoxyadenosine, deoxyguanosine, thymidine, deoxyuridine, deoxycytidine, and deoxyinosine.

[0074] Nucleotides have a structure in which nucleosides and phosphates are bonded.

[0075] Examples of sugars in the nucleoside include ribose or deoxyribose, and the nucleotide can be a ribonucleotide where the sugar is ribose or a deoxyribonucleotide where the sugar is deoxyribose.

[0076] Specific examples of ribonucleotides and deoxyribonucleotides include, for instance, adenosine monophosphate (AMP, also known as adenosine acid), adenosine diphosphate (ADP), adenosine triphosphate (ATP); deoxyadenosine monophosphate (dAMP), deoxyadenosine diphosphate (dADP), deoxyadenosine triphosphate (dATP); guanosine monophosphate (GMP, also known as guanosine acid), guanosine diphosphate (GDP), guanosine triphosphate (GTP); deoxyguanosine monophosphate (dGMP), deoxyguanosine diphosphate (dGDP), deoxyguanosine triphosphate (dGTP); 5-methyluridine monophosphate (TMP), 5-methyluridine diphosphate (TDP), 5-methyluridine triphosphate (TTP); and thymidine monophosphate (dTMP, also known as thymidine acid), thymidine diphosphate (dTD). P), thymidine triphosphate (dTTP); uridine monophosphate (UMP, also known as uridine acid), uridine diphosphate (UDP), uridine triphosphate (UTP); deoxyuridine monophosphate (dUMP), deoxyuridine diphosphate (dUDP), deoxyuridine triphosphate (dUTP); cytidine monophosphate (CMP, also known as cytidine acid), cytidine diphosphate (CDP), cytidine triphosphate (CTP); deoxycytidine monophosphate (dCMP), deoxycytidine diphosphate (dCDP), deoxycytidine triphosphate (dCTP); inosine monophosphate (IMP, also known as inosine acid), inosine diphosphate (IDP), inosine triphosphate (ITP); deoxyinosine monophosphate (dIMP), deoxyinosine diphosphate (dIDP), deoxyinosine triphosphate (dITP), etc.

[0077] In this specification, polynucleotide is a concept encompassing polymers and oligomers containing nucleotides. Examples of polynucleotides include polymers formed by bonding two or more of the ribonucleotides described above, and polymers formed by bonding two or more of the deoxyribonucleotides described above.

[0078] Specific examples of polynucleotides include, for example, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

[0079] There are no particular limitations on the salt of nucleosides, nucleotides or polynucleotides; examples include alkali metal salts or hydrochlorides, with sodium salts being preferred.

[0080] Nucleosides, nucleotides, or polynucleotides may contain known modified bases.

[0081] As analogues of nucleosides, nucleotides, or polynucleotides, they are substances that have the same function as natural nucleic acids. Examples include substances in which any substituent is replaced with any group or atom in the molecule of natural nucleic acids, and substances that have been given any modifications.

[0082] In addition, examples of similar substances include peptide nucleic acid (PNA) and locked nucleic acid (LNA).

[0083] As a decomposition product or fragment of a nucleoside, nucleotide, or polynucleotide, preferably a decomposition product or fragment of a polynucleotide, it can be a hydrolysate.

[0084] Nucleic acids can be the types of nucleic acids or their salts, decomposition products or fragments contained in natural eels.

[0085] Preferably, the nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, salts of nucleosides, salts of nucleotides, and salts of polynucleotides.

[0086] In addition, the nucleic acid class has a structure in which bases are bonded to sugars, and preferably the bases include at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine and hypoxanthine.

[0087] In this specification, nucleic acids refer to structures with base-sugar bonds, and are sometimes simply referred to as "including bases," etc.

[0088] The nucleic acid class has a structure in which bases are bonded to sugars, and more preferably includes at least one base selected from the group consisting of nucleosides, nucleotides, polynucleotides and their salts, wherein the bases include at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine and hypoxanthine. Further preferably, the nucleotides include ribonucleotides or deoxyribonucleotides, and particularly preferably include ribonucleotides.

[0089] Among nucleic acids, those containing purine bases can be interconverted or broken down and used as common raw materials for biosynthesis.

[0090] In addition, nucleic acids, including those with pyrimidine bases, can be interconverted or broken down and used as common raw materials for biosynthesis.

[0091] From this perspective, the nucleic acids contained in the eel fry feed of the preferred embodiment have a structure in which bases are bonded to sugars, and the bases include purine bases and pyrimidine bases.

[0092] The types of bases included in nucleic acids are considered in relation to the overall nucleic acids contained in the eel fry feed of the implementation method.

[0093] For example, when the nucleic acid is a nucleoside or nucleotide, the purine bases and pyrimidine bases contained in the eel fry feed of the embodiment may be contained in different nucleic acid molecules.

[0094] For example, when the nucleic acid is a polynucleotide, the purine bases and pyrimidine bases contained in the eel fry feed of the embodiment can be contained in different nucleic acid molecules, or they can be contained in the same nucleic acid molecule as usual, like DNA and RNA.

[0095] Among the bases mentioned above, adenine, guanine, and hypoxanthine are examples of purine bases.

[0096] Among the bases mentioned above, examples of pyrimidine bases include thymine, uracil, and cytosine.

[0097] In a further preferred embodiment, the nucleic acids contained in the eel fry feed have a structure in which bases are bonded to sugars, wherein the bases include at least one base selected from the group consisting of adenine, guanine and hypoxanthine, and at least one base selected from the group consisting of thymine, uracil and cytosine.

[0098] Furthermore, the nucleic acids contained in the eel fry feed of the embodiment have a structure in which bases are bonded to sugars, and are further preferably selected from at least one of the groups consisting of ribonucleosides, deoxyribonucleosides, ribonucleotides, deoxyribonucleotides, ribonucleic acid and deoxyribonucleic acid and their salts, wherein the bases include at least one base selected from the group consisting of adenine, guanine and hypoxanthine, and at least one base selected from the group consisting of thymine, uracil and cytosine.

[0099] From the perspective of being able to utilize them more efficiently in eel larvae, nucleic acids including various bases are preferred.

[0100] The nucleic acid class has a structure in which bases are bonded to sugars, and preferably the bases include adenine and / or hypoxanthine, guanine, thymine and / or uracil, and cytosine.

[0101] The nucleic acid class has a structure in which bases are bonded to sugars, and more preferably the bases include adenine and / or hypoxanthine, guanine, uracil, and cytosine.

[0102] More preferably, the nucleic acid class has a structure in which bases are bonded to sugars, and the nucleic acid class includes at least one selected from the group consisting of ribonucleosides, ribonucleotides, ribonucleic acids and their salts, and the bases include adenine and / or hypoxanthine, guanine, uracil, and cytosine.

[0103] The exact reasons why feeding eel larvae with nucleic acids can reduce the frequency of individuals exhibiting the aforementioned morphological abnormalities are not yet clear, but the following reasons can be considered. Normally, fish larvae can synthesize nucleic acids in their bodies. However, in eel larvae, the amount of nucleic acid synthesized may be low, requiring them to obtain nucleic acids from their diet, which may not be adequately met by conventional diets. In particular, it is speculated that during the metamorphosis from willow eel to glass eel, a large amount of gene expression and cell division accompany morphological changes, and feeding them with a diet containing nucleic acids could facilitate these processes.

[0104] Relative to the total dry weight (100% by weight) of the eel larvae feed, the content of nucleic acids in the eel larvae feed of the embodiment, by dry weight, can be greater than 0.04% by weight, greater than 0.05% by weight, greater than 0.07% by weight, greater than 0.1% by weight, greater than 0.15% by weight, greater than 0.2% by weight, greater than 0.25% by weight, greater than 0.5% by weight, greater than 0.8% by weight, greater than 0.9% by weight, greater than 1.0% by weight, greater than 1.5% by weight, greater than 2.0% by weight, greater than 2.5% by weight, greater than 3.0% by weight, greater than 3.5% by weight, greater than 3.8% by weight, or greater than 3.9% by weight.

[0105] Feeds for eel larvae containing the aforementioned nucleic acids, calculated relative to the total dry weight (100% by weight) at or above the lower limit, can further effectively reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels.

[0106] Relative to the total dry weight (100% by weight) of the eel larvae feed, the content of nucleic acids in the eel larvae feed of the embodiment may be less than 20% by weight, less than 15% by weight, less than 10% by weight, less than 9% by weight, less than 8% by weight, less than 7% by weight, less than 6% by weight, or less than 5% by weight.

[0107] According to the above-mentioned upper limit value for eel larvae feed containing the aforementioned nucleic acids, calculated based on the dry weight relative to the total dry weight (100% by weight), eel larvae can grow better.

[0108] As an example of the above-mentioned numerical range of nucleic acids contained in the eel larvae feed of the embodiment, relative to the total dry weight (100% by weight) of the eel larvae feed, the content of the nucleic acids in the eel larvae feed of the embodiment, by dry weight, may be greater than 0.04% by weight and less than 20% by weight, may be more than 0.05% by weight and less than 20% by weight, may be more than 0.07% by weight and less than 15% by weight, may be more than 0.1% by weight and less than 15% by weight, may be more than 0.15% by weight and less than 10% by weight, may be more than 0.2% by weight and less than 10% by weight, and may be 0.25% by weight. The content can be 10% or more by weight or less, 0.5% or more by weight or less by weight, 0.8% or more by weight or less by weight, 0.9% or more by weight or less by weight, 1.0% or more by weight or less by weight, 1.5% or more by weight or less by weight, 2.0% or more by weight or less by weight, 2.5% or more by weight or less by weight, 3.0% or more by weight or less by weight, 3.5% or more by weight or less by weight, 3.8% or more by weight or less by weight, or 3.9% or more by weight or less by weight.

[0109] The dry weight of feed or feed ingredients for eel larvae can be determined by drying the feed or feed ingredients at 105°C for 6 hours.

[0110] The content of nucleic acids in the eel larvae feed of the embodiment can be determined by known analytical methods. High-performance liquid chromatography (HPLC) can be used as the analytical method. For example, by using the feed, feed ingredients, or their processed products as the test sample, various nucleic acids can be measured, and their content can be calculated. The test sample can be a sample of feed or feed ingredients that have been treated according to the type of nucleic acid being tested. For example, the test sample can be a sample of feed or feed ingredients that have undergone perchloric acid extraction or nuclease treatment.

[0111] The preferred embodiment of the eel larvae feed contains yeast extract. The yeast extract may contain the aforementioned nucleic acids. Yeast extract is also known as yeast extract. The eel larvae feed of the preferred embodiment may contain nucleic acids and / or yeast extract.

[0112] Relative to the total dry weight (100% by weight) of the eel fry feed, the content of the yeast extract, on a dry weight basis, may be 1% or more, 1% or more and less than 50% by weight, 5% or more and less than 40% by weight, or 10% or more and less than 30% by weight.

[0113] It should be noted that the numerical values ​​of the nucleic acid content exemplified in the above-described embodiment of the eel fry feed (each value exemplified relative to the total dry weight (100% by weight) of the eel fry feed, in the range of greater than 0.04% by weight and less than 20% by weight) can be understood as the numerical values ​​of the nucleic acid content derived from yeast extract.

[0114] From the perspective of better raising eel fry, the eel fry feed of the preferred embodiment also contains milk protein.

[0115] In this instruction manual, "milk protein" refers to proteins derived from milk. Milk proteins are produced from milk and other sources, and are available in various commercially available products. They are one of the most inexpensive and reliably obtainable proteins. Specifically, examples include skim milk powder made from milk and various types of casein.

[0116] Relative to the total dry weight (100% by weight) of the feed for eel fry, the content of the milk protein, on a dry weight basis, may be 10% or more, 10% or more and 80% or less, 20% or more and 60% or less, or 30% or more and 50% or less.

[0117] The feed for eel larvae in this embodiment may also contain a protein source other than milk protein. Since this protein source is preferably a substance that is stably available and easily digestible by eel larvae, it can be bird egg components, chicken egg components, or, from the viewpoint of easier availability, egg yolk powder, for example, is preferred.

[0118] Relative to the total dry weight (100% by weight) of the eel fry feed, the content of the egg component, on a dry weight basis, may be 5% or more by weight, 5% or more by weight and less than 30% by weight, 7% or more by weight and less than 25% by weight, or 10% or more by weight and less than 20% by weight.

[0119] As an example of an implementation of eel larvae feed, the following eel larvae feed can be cited: containing nucleic acids, milk protein, and egg components (e.g., egg yolk powder), wherein, relative to the total dry weight of the eel larvae feed, the content of the nucleic acids is 0.25% to 10% by weight or less, the content of the milk protein is 10% to 80% by weight or less, and the content of the egg components is 5% to 30% by weight or less.

[0120] As an example of an implementation of eel larvae feed, the following eel larvae feed can be cited: containing nucleic acids, yeast extract, milk protein, and egg components (e.g., egg yolk powder), wherein the yeast extract contains the nucleic acids, and the content of the yeast extract is 1% to 50% by weight or less relative to the total dry weight of the eel larvae feed, the content of the milk protein is 10% to 80% by weight or less, and the content of the egg components is 5% to 30% by weight or less.

[0121] In addition to milk protein, fishmeal is an example of a protein source other than milk protein, and from the viewpoint of improving digestibility and absorption, enzyme-treated fishmeal is preferred. Enzyme-treated fishmeal can be a substance made from the flesh of any type of fish, for example, it can be a peptidase, protease, or proteolytic enzyme-treated product of fishmeal.

[0122] Regarding the ratio of milk protein to other proteins, it is preferable that the lactose content, based on dry weight, is less than 10% of the total dry weight of the eel larvae feed. Using low-lactose milk protein or casein can increase the amount of milk protein incorporated.

[0123] As one embodiment of eel fry feed, examples include eel fry feed containing nucleic acids and / or yeast extracts, as well as milk proteins.

[0124] As another embodiment of eel fry feed, examples include eel fry feed containing nucleic acids and / or yeast extracts, milk proteins, and egg yolk powder.

[0125] As another embodiment of eel fry feed, examples include eel fry feed containing nucleic acids and / or yeast extracts, milk protein, egg yolk powder, and fish meal.

[0126] In addition, since the feed for eel larvae in the preferred embodiment can improve the growth and survival rate of eel larvae, it also contains vitamins. Examples of vitamins include, for instance, vitamin C, vitamin A, vitamin E, vitamin B1, vitamin B2, vitamin B6, vitamin B12, vitamin D, vitamin K, niacin, pantothenic acid, folic acid, biotin, etc., as well as choline, inositol, etc.

[0127] In addition, since it can improve growth and survival rates, the eel fry feed of the preferred embodiment contains taurine.

[0128] As another embodiment of eel fry feed, examples of eel fry feed include those containing nucleic acids and / or yeast extracts, milk protein, egg yolk powder, fish meal, vitamins, and taurine.

[0129] In addition, since it is generally preferred to feed eel larvae with n-3 highly unsaturated fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), the eel larvae feed of the preferred embodiment contains fish oil such as liver oil containing the above-mentioned n-3 highly unsaturated fatty acids.

[0130] The eel fry feed of the embodiment can contain soybean peptides (preferably soybean peptides after phytic acid reduction treatment) as other arbitrary ingredients.

[0131] The eel larvae feed of the embodiment can be, for example, a feed in which nucleic acids and / or yeast extracts are added to any basic eel larvae feed. Here, the basic eel larvae feed refers to feed that is fed to eel larvae and enables them to grow and metamorphose into eel juveniles, such as the eel larvae feed described in Patent Document 2 and Patent Document 3. As for the amount of nucleic acid and / or yeast extract added, the amount of the nucleic acid content relative to the total dry weight of the eel larvae feed can be given as exemplified above.

[0132] On the other hand, the eel larvae feed of this embodiment is useful as a substitute for feed containing shark egg components. Therefore, the eel larvae feed of the preferred embodiment does not contain shark egg components. In this specification, "shark egg components" refers to components derived from shark eggs. Examples of shark eggs include those from the dogfish (Caryota esculenta).

[0133] The eel fry feed of the embodiment can be in powder form, and from the perspective of suitability for distribution and storage, it can be a dry powder. In addition, from the perspective of easy swallowing by fry, when feeding eel fry, appropriate amounts of liquid such as water or seawater can be added to the powdered eel fry feed to obtain a paste-like eel fry feed before feeding it to the eel fry.

[0134] By feeding eel larvae the eel larvae feed according to the implementation method, the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels can be reduced.

[0135] In this instruction manual, morphological abnormalities refer to severe deformities of the spine, such as spinal curvature, wavy deformity, torsion, and broken neck (see reference). Figure 2 Severe deformation refers to deformation of a degree that is perceptible to an observer when viewed through an optical microscope.

[0136] The rate of morphological abnormalities in the produced eel juveniles can be below 35%, below 30%, below 25%, below 20%, below 15%, or below 10%, based on the number of individuals observed (more than 16).

[0137] <Method for manufacturing feed for eel fry>

[0138] The method for manufacturing eel larvae feed according to the embodiments includes mixing various raw materials and raw material components in one go or in an appropriate order to obtain eel larvae feed according to the embodiments.

[0139] According to the method for manufacturing eel fry feed according to the embodiment, the eel fry feed of the embodiment can be manufactured.

[0140] Examples of raw materials, raw material components, and their contents can be cited in the above-mentioned "Feed for Eel Fry". Besides nucleic acids, other raw materials and raw material components, besides those mentioned above, include yeast extract, milk protein, egg yolk powder, fish meal, vitamins, taurine, and liver oil from fish, among other arbitrary ingredients. Water, seawater, and other liquid substances can be appropriately added to the feed for eel fry.

[0141] As an example of a method for manufacturing feed for eel larvae, the following method for manufacturing feed for eel larvae includes: relative to the total dry weight (100% by weight) of the feed for eel larvae, adding the nucleic acid and / or yeast extract to such that the feed contains at least 0.25% by weight of nucleic acid based on dry weight.

[0142] As an example of a method for manufacturing feed for eel larvae, the following method for manufacturing feed for eel larvae includes: relative to the total dry weight (100% by weight) of the feed for eel larvae, adding the nucleic acid and / or yeast extract to such that the feed contains less than 10% by weight of nucleic acid based on dry weight.

[0143] As an example of a method for manufacturing feed for eel larvae, the following method for manufacturing feed for eel larvae includes: relative to the total dry weight (100% by weight) of the feed for eel larvae, adding the nucleic acid and / or yeast extract, such that the feed contains 0.25% by weight or more and 10% by weight of nucleic acid on a dry weight basis.

[0144] The eel larvae feed of the embodiment can also be manufactured, for example, by adding nucleic acids and / or yeast extracts to any eel larvae basic feed. Here, the eel larvae basic feed refers to feed that is given to eel larvae and enables them to metamorphose into eel juveniles.

[0145] As for the amount of nucleic acid and / or yeast extract added, examples can be given of the amount of nucleic acid content relative to the total dry weight of the eel larvae feed, which satisfies the above examples.

[0146] The eel fry feed of the embodiment can be manufactured, for example, by combining 0.25 to 20 parts by weight of nucleic acid and / or yeast extract, 10 to 50 parts by weight of milk protein, 5 to 30 parts by weight of egg yolk powder, and 10 to 50 parts by weight of fish meal. The parts by weight of these raw materials can be in the state (e.g., wet weight ratio) for use in feed manufacturing.

[0147] In one embodiment, the present invention provides the use of nucleic acids for manufacturing feed for eel larvae.

[0148] In one embodiment, the present invention provides the use of yeast extract for manufacturing feed for eel fry.

[0149] Methods of Eel Production

[0150] The eel production method of this embodiment includes feeding eel larvae with the eel larvae feed of this embodiment.

[0151] In addition, as one embodiment, a method for reducing the frequency of occurrence of glass eel individuals exhibiting morphological abnormalities is provided, the method comprising feeding eel larvae with eel larvae feed of the embodiment.

[0152] As an example of an eel fry feed, the feed described in the above-mentioned "Eel Fry Feed" can be cited.

[0153] There are no particular restrictions on the method of raising eel fry, and it can be carried out according to well-known eel fry raising methods. As an example, eel fry can be raised at a water temperature of 23-25°C and a salinity concentration of 16-34 psu (practical salinity unit).

[0154] There are no particular restrictions on the method of feeding eel larvae; they can be fed according to the conventional feeding methods for eel larvae. As an example, the feeding frequency for eel larvae can be more than once a day, for example, 3 to 5 times a day (e.g., preferably with a feeding interval of at least 2 hours). The amount of eel larvae feed can be adjusted appropriately based on the feeding status of the eel larvae; feeding until they are full is preferred.

[0155] The feeding period for eel larvae in this embodiment is not particularly limited as long as it falls within the larval stage. However, from the viewpoint of more effectively suppressing morphological abnormalities during metamorphosis, it is preferable to include at least the period before the onset of metamorphosis into glass eel. As an example, one could exemplify feeding eel larvae, preferably from 10 days prior to the start of metamorphosis until the completion of metamorphosis, more preferably from 30 days prior to the start of metamorphosis until the completion of metamorphosis, and even more preferably from 60 days prior to the start of metamorphosis until the completion of metamorphosis, at least once a day. The feeding period for eel larvae in this embodiment can be continuous or discontinuous; for example, it can be 10 days or more, 50 days or more, 100 days or more, or 150 days or more.

[0156] It should be noted that by appropriately setting a period of feeding eel fry without food before the onset of metamorphosis, the onset of metamorphosis can also be induced.

[0157] The preferred method for producing eels according to the embodiments includes a method for producing artificial seedlings by feeding eel larvae with the feed for eel larvae according to the embodiments.

[0158] The production of artificial seedlings here refers to the process of artificially spawning and hatching eel fry to grow into glass eels.

[0159] The eel production method described in this embodiment enables fully artificial aquaculture. Fully artificial aquaculture refers to artificially spawning and hatching eels, raising them to adulthood, and then using the eggs produced by these adult eels to cultivate the next generation of adult eels.

[0160] Inhibitor of Morphological Abnormalities in Eel Juveniles

[0161] The morphological abnormality inhibitor for eel juveniles in this implementation method contains nucleic acids as active ingredients.

[0162] The eel juvenile morphological abnormality inhibitor of the implementation method can contain yeast extract as an active ingredient.

[0163] Nucleic acid compounds and yeast extracts contained in eel fry morphological abnormalities can be cited as examples from the aforementioned "Feed for Eel Fry".

[0164] The morphological abnormality inhibitor for eel fry, for example, can be administered to eel fry by adding it to any eel feed, preferably eel larvae feed, to reduce the frequency of occurrence of glass eel individuals exhibiting morphological abnormalities.

[0165] In one embodiment, the present invention provides the use of nucleic acid classes as inhibitors of morphological abnormalities in eel juveniles.

[0166] In one embodiment, the present invention provides the use of yeast extract as an inhibitor of morphological abnormalities in eel juveniles.

[0167] The eel larvae feed, eel production method, and eel juvenile morphological abnormality inhibitor described above enable the artificial rearing of eel larvae using a stable supply of raw materials, and produce high-quality glass eels. The eel larvae feed, eel production method, and eel juvenile morphological abnormality inhibitor of this embodiment are extremely useful for realizing the long-awaited commercialization of fully artificially cultured and mass-produced eels.

[0168] Example

[0169] The present invention will now be described in more detail with reference to embodiments, but the present invention is not limited to the embodiments described below.

[0170] [Experiment 1] Evaluation of the effect of adding nucleic acids to feed on the frequency of morphological abnormalities

[0171] (Feed ingredients)

[0172] • Dried egg yolk powder (manufactured by Kewpie Tamago Co., Ltd., dried egg yolk number 1).

[0173] • Enzyme-treated fishmeal (manufactured by Scientific Feed Research Institute, Co., Ltd., CPSP SPECIAL G).

[0174] Casein Sodium (manufactured by Nippon Shinyaku Co., Ltd., sodium casein LW).

[0175] • Skim milk powder (manufactured by Yotsuba Dairy Co., Ltd., Hokkaido skim milk powder).

[0176] • Soybean peptides (manufactured by Nippon Pharmaceutical Co., Ltd., peptone N).

[0177] • Yeast extract (high IMP) (manufactured by Xingren Life Science Co., Ltd., Aromild (registered trademark)).

[0178] • Nucleic acid mixtures (substances made by mixing disodium salts of AMP, IMP, GMP, CMP, and UMP in equal weights).

[0179] AMP: Disodium adenosine 5'-monophosphate (Fujifilm and Wako Pure Chemical Industries, Ltd. QB-7150)

[0180] IMP: Inosine 5'-monophosphate disodium salt (NACALAITESQUE, 06400-22)

[0181] GMP: Guanosine 5'-monophosphate disodium salt (Fujifilm and Kazumitsu Chemical Co., Ltd. QB-3304)

[0182] CMP: Cytidine 5'-monophosphate disodium salt (Tokyo Kasei Corporation C0524)

[0183] UMP: Urate 5'-monophosphate disodium salt (Fujifilm and Koichi Chemical Co., Ltd. QR-1512)

[0184] Taurine (manufactured by NACALAI TESQUE Co., Ltd., reagent taurine)

[0185] • Vitamin blend (manufactured by Japan Nutrition Co., Ltd., vitamins for fisheries research / educational institutions)

[0186] ·Cod liver oil (High Carol E, manufactured by Kanematsu Shin Toa Foods Co., Ltd.)

[0187] (method)

[0188] Five-day-old eel larvae were housed in 12 rearing tanks (acrylic bowl-shaped tanks, approximately 10L in capacity), each holding 500 larvae. Six-day-old eel larvae were fed shark egg substitute feed (FSD, a modified version of the fishmeal feed described in Table 1 of Patent Document 3), and were pre-reared until 80 days of age. Feeding was performed five times daily (every two hours apart), with a feeding amount of 7–10 mL per feeding. The water temperature was maintained at 23°C, and the water flow rate was 0.5–0.7 L / min. The tanks were changed after the final feeding each day.

[0189] Larvae were collected at 80 days of age and redistributed to 12 rearing tanks with 80 larvae per tank. The feed ingredients were mixed according to the proportions (g) shown in Table 1 to prepare the experimental feeds. After 81 days of age, experimental zones were established for each of the experimental feeds shown in Table 1. Six experimental zones were set up: a control zone fed with FSD (FSD zone), a zone fed with a feed containing 0.5g, 1.0g, 2.0g, or 4.0g of nucleic acid mixture added to the FSD feed (FSD+NM zone), and a zone fed with a feed in which soybean peptides in the FSD feed were replaced with yeast extract and the proportions of some ingredients were changed (FSY zone). Each experimental zone had two tanks. Basic rearing conditions remained the same as before 80 days of age, and feeding continued until 340 days of age. After 341 days of age, the larvae were kept without feed to induce metamorphosis.

[0190] Individuals showing signs of metamorphosis (such as forward movement of the anus and a decrease in body height) were removed from their rearing tanks and placed individually in 250mL polycarbonate containers filled with water. They were kept unfed and the metamorphosis was observed. The moment when the body shape completely transformed into that of a glass eel was defined as the completion of metamorphosis. After anesthesia, photographs were taken, and the body shape at the point of completion of metamorphosis was recorded as image data.

[0191] For the identification of morphological abnormalities, individuals exhibiting severe spinal deformities are defined as abnormal, and the assessment is conducted independently by two skilled assessors. The assessment results are reviewed, and for individuals where the assessors disagree, a consultation is held. An example of an individual assessed as "no morphological abnormality" or "possessing morphological abnormality" is shown below. Figure 2 .

[0192] To verify the effect of added nucleic acid mixtures or yeast extracts on the frequency of morphological abnormalities, binary data related to the presence or absence of morphological abnormalities at the completion of metamorphosis were used as the dependent variable, and feed type (experimental area) was used as the independent variable. Logistic regression analysis was used, and JMP16.0 software was used to calculate the odds ratio and 95% confidence interval for the occurrence of morphological abnormalities among different feeds.

[0193] Table 1

[0194]

[0195] *Calculated based on the amount of nucleic acid mixture added, total nucleotides and total nucleosides in yeast extract (analytical value), and the amount of nucleic acids from the raw materials (analytical value).

[0196] In Experiments 1-3, the "-" in Tables 1, 3, and 6 indicates that the raw material is not used.

[0197] In experiments 1-3, the total dry weight was defined as the sum of the values ​​of the feed ingredients after drying at 105°C for 6 hours.

[0198] When using nucleic acids as disodium salts, the amount of nucleic acid is expressed as 0.88 times the weight of the nucleic acid itself after removing the disodium component.

[0199] The “Nucleic Acid Content (wt%)” item in the table shows the percentage (wt%) of the nucleic acid content relative to the total dry weight of the feed.

[0200] (result)

[0201] The number of individuals beginning metamorphosis started at 138 days of age, and the cumulative number of individuals starting metamorphosis up to 340 days of age was 308 (FSD region: 29, FSD+NM0.5 region: 48, FSD+NM1.0 region: 52, FSD+NM2.0 region: 65, FSD+NM4.0 region: 54, FSY region: 60). The number of individuals completing metamorphosis was 283 (FSD region: 27, FSD+NM0.5 region: 43, FSD+NM1.0 region: 50, FSD+NM2.0 region: 57, FSD+NM4.0 region: 49, FSY region: 57).

[0202] The frequency and ratio of morphological anomalies in each test area are shown in the figure. Figure 3 See Table 2. Compared to the FSD region (as a control), in the four test regions with added nucleic acid mixtures, higher concentrations of the nucleic acid mixture resulted in lower odds ratios for morphological abnormalities, with the greatest reduction observed in the FSY region. The reduction rates, estimated based on the odds ratios at 100% of the frequency in the FSD region, were 50.0% for the FSD+NM0.5 region, 63.6% for the FSD+NM1.0 region, 69.1% for the FSD+NM2.0 region, 75.8% for the FSD+NM4.0 region, and 94.7% for the FSY region, indicating that the addition of nucleic acid mixtures or yeast extracts can reduce the frequency of morphological abnormalities. The proportion of individuals exhibiting morphological abnormalities decreased depending on the nucleic acid content in the feed.

[0203] Table 2

[0204]

[0205] *A lower odds ratio indicates a lower probability of severe spinal abnormalities relative to FSD. A value below 1 at the 95% confidence interval is statistically significant.

[0206] [Experiment 2] Study of various yeast extracts

[0207] The (feed ingredients) differ from those in Experiment 1 above.

[0208] • Yeast extract (high AMP) (manufactured by Xingren Life Science Co., Ltd., Nucleamine (registered trademark)).

[0209] • Yeast extract (reagent) (manufactured by Sigma-Aldrich, Yeast Extract 09182).

[0210] (method)

[0211] Six-day-old eel larvae were housed in 14 rearing tanks (semi-tubular polycarbonate tanks, approximately 30L in capacity), each holding 1000–1500 larvae. The 6-day-old eel larvae were fed shark egg substitute feed (FSD) and pre-reared until 39 days of age. Feeding was conducted five times daily (every 2.5 hours apart), with a feed volume of 30–40 mL per feeding. The water temperature was maintained at 23°C, and the water inflow rate was 1.6–1.7 L / min. The tanks were changed after the final feeding each day.

[0212] Larvae were collected at 40 days of age and redistributed into 14 groups of 400 larvae per 30L semi-tube tank. The feed ingredients were mixed according to the proportions (g) shown in Table 3 to prepare the experimental feeds. After 40 days of age, experimental zones were established, each administering one of the four experimental feeds shown in Table 3. Each experimental zone contained either 3 or 4 tanks (FSD zone: 4, FSY2 zone: 4, FSX zone: 3, FSZ zone: 3). Basic rearing conditions remained the same as before 39 days of age, with feeding continuing until 304 days of age. From 305 to 330 days of age, the larvae were kept without feeding to induce metamorphosis.

[0213] The definitions of the onset and completion of metamorphosis, the methods for recording phenotypes, the identification of morphological abnormalities, and the statistical analysis are the same as in Experiment 1.

[0214] Table 3

[0215]

[0216] *Calculated based on the total nucleotides and total nucleosides (analytical values) in each yeast extract and the amount of nucleic acids from the raw materials (analytical values).

[0217] (result)

[0218] The nucleotide content of the feed FSD and the three added yeast extracts was analyzed. The content of various nucleic acids was determined in samples extracted with 5% perchloric acid.

[0219] For feed FSD and reagent yeast extract (manufactured by Sigma-Aldrich), samples treated with nuclease P1 were also analyzed to determine the content of various nucleic acids (in the analysis of 5'-inosine, samples extracted with 5% perchloric acid were analyzed to determine the content).

[0220] It should be noted that the main source of nucleic acids in yeast extracts (Aromild and Nucleamine, manufactured by Kojin Life Sciences Co., Ltd.) is RNA. During the manufacturing process, RNA undergoes degradation; therefore, the nucleic acids in yeast extracts exist in the form of nucleotides. For reagent yeast extracts (manufactured by Sigma-Aldrich), nucleotides were not detected in feed without enzymatic degradation using nuclease P1. Therefore, the nucleic acids in reagent yeast extracts are contained as ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

[0221] The analytical results of nucleotides contained in the feed FSD and the three yeast extracts used are presented as the content (wt%) per unit dry weight of the feed FSD or yeast extract, as shown in Table 4. The sum of the total nucleotides and total nucleosides in the analytical values ​​is taken as the nucleic acid content.

[0222] In feed FSD, almost no nucleic acids are present; all analytical items except GMP are below the detection limit (0.01g / 100g). Aromild contains IMP, UMP, GMP, and CMP, with total nucleotides of 23.05% by weight and total nucleosides of 1.44% by weight. Nucleamine contains AMP, UMP, GMP, and CMP, with total nucleotides of 24.86% by weight and total nucleosides of 1.74% by weight. Reagent yeast extract contains AMP, UMP, GMP, and CMP, with total nucleotides of 4.24% by weight and total nucleosides of 1.22% by weight.

[0223] It should be noted that in the region where 5'-thymidine is below the detection limit, the levels of deoxynucleotides, deoxynucleosides, and DNA are presumed to be below the detection limit.

[0224] Table 4

[0225]

[0226] By the end of the breeding program, a total of 163 tails had begun metamorphosis (FSD area: 18 tails, FSY2 area: 59 tails, FSX area: 64 tails, FSZ area: 22 tails), and a total of 138 tails had completed metamorphosis (FSD area: 16 tails, FSY2 area: 46 tails, FSX area: 59 tails, FSZ area: 17 tails).

[0227] The frequency and ratio of morphological anomalies in each test area are shown in the figure. Figure 4See Table 5. Compared to the feed FSD zone, the odds ratios for morphological abnormalities decreased in the three test zones where yeast extract was added. The decrease rates, estimated based on the odds ratios at 100% of the occurrence frequency in the FSD zone, were 68.6% in FSY2, 96.5% in FSX, and 58.3% in FSZ, indicating that the frequency of morphological abnormalities can be reduced by adding yeast extract containing nucleic acids.

[0228] Table 5

[0229]

[0230] *The lower the ratio, the lower the probability of developing severe spinal abnormalities relative to FSD.

[0231] There is a significant difference when the 95% confidence interval is less than 1.

[0232] [Experiment 3] Study on the content of nucleic acids in feed

[0233] The feed ingredients differ from those in experiments 1 and 2 above.

[0234] • Nucleic acid mixture (manufactured by MARUGO Co., Ltd., a mixture of 5'-ribonucleotide sodium nucleic acid, IMP and GMP).

[0235] • Vitamin mixture (see Furuita et al. (2014) Fisheries Science, 80, 581-587).

[0236] Taurine (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.)

[0237] (method)

[0238] Six-day-old eel larvae were housed in seven rearing tanks (acrylic bowl-shaped tanks, approximately 10L in capacity), each holding 250 larvae. The feed ingredients were mixed according to the proportions (g) shown in Table 6 to prepare the experimental feeds. From seven to nineteen days of age, the eel larvae were fed the experimental feeds shown in Table 6. Feeding was conducted five times daily (2-hour intervals), with a feeding volume of 7 mL per feeding. The water temperature was 23°C, and the water flow rate was 0.4–0.6 L / min. The tanks were changed after the final feeding each day. Seven experimental zones were established, each feeding zone containing one tank of one feed containing 1g, 2g, 5g, 10g, 15g, or 20g of a nucleic acid mixture (a mixture of IMP and GMP) added to the feed's free radical saturation (FSD).

[0239] At 20 days of age, 31–33 fish were randomly selected from each tank, anesthetized, and photographed under a stereomicroscope. Total length and body height were determined using ImageJ image analysis. For each experimental area, an S-shaped curve was fitted to the relationship between average total length, average body height, and nucleic acid content (the ratio of nucleic acid content by dry weight to the total dry weight of the feed (wt%)), and the inflection point at 50% of the maximum response was estimated.

[0240] Table 6

[0241]

[0242] *Calculated based on the amount of nucleic acid mixture added and the amount of nucleic acids from the raw materials (analytical value).

[0243] (result)

[0244] The relationship between the average total length and average body height of 20-day-old animals and the nucleic acid content of their feed is shown in the figure. Figure 5 The estimated inflection points and 95% confidence intervals for each parameter are 9.99 (7.7–12.3) and 9.79 (7.8–11.8), respectively. This indicates that, for example, feeding eel larvae with a diet containing less than 10% by weight of nucleic acids per unit dry weight can achieve even better growth.

[0245] The various components and combinations in each embodiment are merely examples. Additions, omissions, substitutions, and other modifications to the components are possible without departing from the intent of the invention. Furthermore, the invention is not limited to the various embodiments, but is defined only by the scope of the claims.

[0246] Industrial applicability

[0247] According to the present invention, by feeding eel larvae with nucleic acids, the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from eel larvae to glass eels can be reduced, and therefore it can be used industrially.

Claims

1. A feed for eel fry, wherein, The feed for eel fry contains nucleic acids.

2. The eel fry feed as described in claim 1, wherein, The content of the nucleic acids, relative to the total dry weight of the eel fry feed, is 0.25% by weight or more.

3. The eel fry feed as described in claim 1 or 2, wherein, The content of nucleic acids, relative to the total dry weight of the eel fry feed, is less than 10% by weight.

4. The eel fry feed as described in claim 1 or 2, wherein, The nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, salts of nucleosides, salts of nucleotides, and salts of polynucleotides.

5. The eel fry feed as described in claim 1 or 2, wherein, The nucleic acids described have a structure in which bases are bonded to sugars. The bases include at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

6. The eel fry feed as described in claim 1 or 2, wherein, The nucleic acids described have a structure in which bases are bonded to sugars. The bases include purine bases and pyrimidine bases.

7. The eel fry feed as described in claim 1 or 2, wherein, The feed for eel fry contains yeast extract, and the yeast extract contains the nucleic acids.

8. The eel fry feed as described in claim 1 or 2, wherein, The feed for eel fry does not contain shark egg components.

9. The eel fry feed as described in claim 1 or 2, wherein, The feed for eel fry also contains milk protein.

10. The eel fry feed as described in claim 1 or 2, wherein, The feed for eel fry also contains egg components.

11. A method for producing eels, wherein, The method for producing eels includes feeding eel larvae the eel larvae feed as described in claim 1 or 2.

12. The method for producing eel as described in claim 11, wherein, The feeding refers to feeding the animal to its full capacity.

13. The method for producing eel as described in claim 11, wherein, The method described above produces artificial seedlings of eels.

14. An inhibitor of abnormal morphology in eel juveniles, wherein, The eel juvenile morphological abnormality inhibitor contains nucleic acids as its active ingredient.

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