Feed for eel larvae used to inhibit morphological abnormalities in eel fry, eel production method, and an eel larvae morphological abnormality inhibitor used to manufacture the feed for eel larvae used to inhibit morphological abnormalities in eel fry.

Abstract

A feed for eel larvae contains nucleic acids. The content of the aforementioned nucleic acids relative to the total dry weight of the feed for eel larvae is preferably 0.25% by weight or more, on a dry weight basis. The feed for eel larvae may contain yeast extract, and the yeast extract may contain the aforementioned nucleic acids.

Description

Technical Field

[0001] This invention relates to a feed for eel fry, a method for producing eels, and an inhibitor of abnormal morphology in eel fry. This application 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. Prior Technology

[0002] As breeding stock for eel farming, glass eels are now the main species used, and wild-caught glass eels are used for farming. However, the catch of natural glass eels has plummeted. In order to mitigate the impact on natural eels and to ensure stable eel farming production, the industry is seeking to develop an artificial production technology for glass eels.

[0003] The fisheries research and education institution (formerly the Fisheries Research and Development Centre) to which the inventor of this case belongs successfully bred glass eels artificially for the first time in the world in 2002. The process was extremely difficult, requiring more than 40 years of research before it was achieved. The natural growth environment and ecology of eel larvae are almost entirely unknown, so the development of feed that can support the growth of eels during the larval stage requires a great deal of trial and error. In particular, the process of metamorphosis from egg-hatched eels (leptocephalus) to juveniles (glass eels) is the most difficult hurdle.

[0004] Shark egg powder has been proposed as an initial feed for eel larvae (Patent Document 1). However, despite numerous attempts, no other feed has been found that has any effect on the feeding or growth of eel larvae. Furthermore, even the aforementioned shark egg powder cannot induce the growth and metamorphosis of the willow eel into the glass eel.

[0005] However, later, through the addition of krill decomposed products and / or soybean peptides with reduced phytic acid to shark eggs, the metamorphosis into glass eels was first confirmed (Patent Document 2). Thus, shark eggs (especially white-spotted dogfish eggs) became the main material for eel larvae feed.

[0006] However, feed made from natural resources is difficult to supply in large quantities and stably, and there are concerns about the continued stable supply of white-spotted dogfish eggs due to the depletion of resources.

[0007] 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 replace the previous feed for white-spotted dogfish eggs as a stable feed. [Previous Technical Documents] [Patent Literature]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-253111. [Patent Document 2] Japanese Patent Application Publication No. 2005-13116. [Patent Document 3] Japanese Patent Application Publication No. 2018-153147. Summary of the Invention

[0009] [The problem that the invention aims to solve] Eels exhibit a very unique growth process. Figure 1 illustrates the growth process of eels from fertilized eggs to glass eels. After hatching from fertilized eggs, the larvae undergo a pre-leptocephalus stage, developing into the larval stage known as the willow leaf eel. The willow leaf eel is transparent and has a distinctive shape resembling a willow leaf. Subsequently, the willow leaf eel undergoes metamorphosis, becoming a glass eel juvenile.

[0010] However, in the case of raising eels using the milk protein-containing feed shown in Patent Document 3, about half of the individuals exhibited morphological abnormalities during the metamorphosis from eel larvae to glass eels (eel juveniles).

[0011] This invention was made to eliminate the problems mentioned above, and its purpose is to provide a feed for eel larvae. By feeding eel larvae, the frequency of individuals exhibiting morphological abnormalities during the metamorphosis of eel larvae into glass eels can be reduced. In addition, the purpose of this invention is to provide a method for producing eels that can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis process from eel larvae to glass eels. In addition, the purpose of this invention is to provide an inhibitor of morphological abnormalities in eel juveniles, which can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis process from eel larvae to glass eels. [Methods used to solve problems]

[0012] In order to solve the above-mentioned problems, the inventors of this invention conducted in-depth research and found that by feeding eel fry with feed containing nucleic acids, the frequency of the occurrence of individuals exhibiting abnormal morphology can be reduced, thereby completing the present invention. That is, one aspect of the present invention includes the following aspects.

[0013] (1) A feed for eel fry containing nucleic acids. (2) The feed for eel fry as described in (1) above, wherein the content of the aforementioned nucleic acid is 0.25% by weight or more relative to the total dry weight of the aforementioned feed for eel fry. (3) The eel larvae feed as described in (1) or (2) above, wherein the content of the aforementioned nucleic acids is less than 10% by weight relative to the total dry weight of the aforementioned eel larvae feed. (4) The eel fry feed described in any of (1) to (3) above, wherein the aforementioned nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids. (5) The eel fry feed described in any of (1) to (4) above, wherein the aforementioned nucleic acid has a structure formed by the combination of a base and a sugar; wherein the aforementioned base includes at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine and hypoxanthine. (6) The eel fry feed described in any of (1) to (5) above, wherein the aforementioned nucleic acid has a structure formed by the combination of bases and sugars; the aforementioned bases include purine bases and pyrimidine bases. (7) The eel fry feed described in any of (1) to (6) above, wherein the eel fry feed contains yeast extract and the yeast extract contains the aforementioned nucleic acid. (8) The eel larvae feed described in any of (1) to (7) above, wherein the eel larvae feed does not contain shark egg components. (9) The feed for larvae of eels as described in any of (1) to (8) above, wherein the feed for larvae of eels further comprises milk protein. (10) The eel fry feed described in any of (1) to (9) above, wherein the eel fry feed further includes an egg component. (11) A method for producing eels, comprising feeding eel fry with eel fry feed as described in any one of (1) to (10) above. (12) The eel production method described in (11) above, wherein the aforementioned feeding is saturation feeding. (13) The eel production method described in (11) or (12) above is the production of artificial seedlings. (14) An inhibitor of abnormal morphology in eel juveniles, which contains nucleic acids as active ingredients.

[0014] In addition, the present invention may have the following forms. (15) The morphological abnormality inhibitor of eel juveniles as described in (14) above, wherein the aforementioned nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids. (16) The morphological abnormality inhibitor of eel juveniles as described in (14) or (15) above, wherein the aforementioned nucleic acid has a structure formed by the combination of a base and a sugar; the aforementioned base includes at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine and hypoxanthine. (17) An inhibitor of abnormal morphology of eel juveniles as described in any of (14) to (16) above, wherein the aforementioned nucleic acid has a structure formed by the combination of bases and sugars; the aforementioned bases include purine bases and pyrimidine bases. (18) The eel juvenile morphological abnormality inhibitor described in any of (14) to (17) above contains a yeast extract, which contains the aforementioned nucleic acid class. [Invention Benefits]

[0015] According to the present invention, a feed for eel larvae can be provided, which can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis of eel larvae into glass eels by feeding the eel larvae. In addition, according to the present invention, a method for producing eels can be provided, which can reduce the frequency of individuals exhibiting morphological abnormalities during the metamorphosis of eel larvae into glass eels by feeding them the aforementioned eel larvae feed. 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 of eel larvae into glass eels. Simple Explanation of the Diagram

[0016] [Figure 1] is a diagram illustrating the growth process of an eel from its natural state to that of a glass eel. [Figure 2] is an image of a glass eel that was determined to be "without morphological abnormality" or "with morphological abnormality" in the embodiment. [Figure 3] is a chart showing the frequency of morphological abnormalities in each experimental area in Experiment 1. [Figure 4] is a chart showing the frequency of morphological abnormalities in each experimental area in Experiment 2. [Figure 5] 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 fry. Implementation

[0017] The following describes the implementation of the present invention, including feed for eel fry, eel production method, and inhibitor of abnormal morphology in eel fry.

[0018] Feed for fry eels The feed for juvenile eels contains nucleic acids. By feeding juvenile eels with feed containing nucleic acids, the juvenile eels can grow into glass eels (young eels) and the frequency of individuals exhibiting morphological abnormalities can be reduced.

[0019] In this specification, "eel larvae" refers to eels in the state before they complete metamorphosis into glass eels. Examples of eel larvae include: early-stage willow leaf eels, willow leaf eels, and eels undergoing metamorphosis into glass eels. In this specification, "eel juveniles" refers to eels that have completed metamorphosis into glass eels, such as eels with a pre-anal length / total length ratio of less than 40% and a body height / total length ratio of less than 7%. Glass eels are an example of eel juveniles.

[0020] The frequency of individuals exhibiting morphological abnormalities is reduced. For example, this can be confirmed by comparing the frequency of individuals exhibiting morphological abnormalities during metamorphosis in a group of eel larvae fed a control group and a group of eel larvae fed a morphological control group.

[0021] The types of eels that are used as feed for eel fry can be any species of eel, such as Japanese eel (Anguilla japonica), European eel (Anguilla anguilla), and American eel (Anguilla rostrata), with Japanese eel being the preferred choice.

[0022] In this specification, "nucleic acid class" includes the concepts of nucleosides, nucleotides, polynucleotides, salts of these nucleic acids, analogs of these nucleic acids, decomposition products, and fragments.

[0023] Nucleosides have a structure formed by the combination of a base and a sugar. Examples of the aforementioned bases include: adenine, guanine, thymine, uracil, cytosine, hypoxanthine, etc. The aforementioned bases are preferably nucleic acid bases. Examples of sugars mentioned above include ribose or deoxyribose. Nucleosides can be ribonucleotides containing ribose or deoxyribonucleotides containing deoxyribose.

[0024] Specific nucleosides include, for example: adenosine, guanosine, 5-methyluridine, uridine, cytidine, inosine, deoxyadenosine, deoxyguanosine, thymidine, deoxyuridine, deoxycytidine, and deoxyinosine, etc.

[0025] Nucleotides have a structure formed by the combination of nucleosides and phosphates. As sugars in the aforementioned nucleosides, ribose or deoxyribose can be listed, and nucleotides can be ribonucleotides with ribose as the sugar or deoxyribonucleotides with deoxyribose as the sugar.

[0026] Specific examples of ribonucleotides and deoxyribonucleotides include: adenosine monophosphate (also known as AMP, adenosine acid), adenosine diphosphate (ADP), adenosine triphosphate (ATP); deoxyadenosine monophosphate (dAMP), deoxyadenosine diphosphate (dADP), deoxyadenosine triphosphate (dATP); guanosine monophosphate (also known as GMP, guanylic 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); thymidine monophosphate (also known as dTMP, thymidine acid), thymidine diphosphate (dTMP ... Uridine monophosphate (DP), thymidine triphosphate (dTTP); uridine monophosphate (also known as UMP, uridine acid), uridine diphosphate (UDP), uridine triphosphate (UTP); deoxyuridine monophosphate (dUMP), deoxyuridine diphosphate (dUDP), deoxyuridine triphosphate (dUTP); cytidine monophosphate (also known as CMP, cytidine acid), cytidine diphosphate (CDP), cytidine triphosphate (CTP); deoxycytidine monophosphate (dCMP), deoxycytidine diphosphate (dCDP), deoxycytidine triphosphate (dCTP); inosine monophosphate (also known as IMP, inosine acid), inosine diphosphate (IDP), inosine triphosphate (ITP); deoxyinosine monophosphate (dIMP), deoxyinosine diphosphate (dIDP), deoxyinosine triphosphate (dITP), etc.

[0027] In this specification, polynucleotides include the concepts of polymers of nucleotides and oligomers. Examples of polynucleotides include polymers formed by the combination of two or more of the ribonucleotides exemplified above, and polymers formed by the combination of two or more deoxyribonucleotides exemplified above.

[0028] Specific examples of polynucleotides include deoxyribonucleic acid (DNA), ribonucleic acid (RNA), etc.

[0029] There are no particular limitations on whether it is a salt of nucleosides, nucleotides, or polynucleotides; examples include alkali metal salts or hydrochlorides, with sodium salts being preferred.

[0030] Nucleosides, nucleotides, or polynucleotides may also contain known modified bases.

[0031] As analogues to nucleosides, nucleotides, or polynucleotides, examples include those that have the same function as natural nucleic acids and are formed by replacing any base or atom in the molecule of natural nucleic acids with any substituent or by giving it any modification. In addition, peptide nucleic acid (PNA) or LNA (Locked nucleic acid) can also be cited as analogues.

[0032] As a decomposition product or fragment of nucleosides, nucleotides, or polynucleotides, it is suitable to be a decomposition product or fragment of polynucleotides, or it may be a hydrolysate.

[0033] Nucleic acids can be naturally occurring types found in eels, or their salts, decomposition products, or fragments.

[0034] The aforementioned nucleic acid class is preferably at least one of the group consisting of nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids.

[0035] In addition, it is preferable that the aforementioned nucleic acid class has a structure formed by the combination of a base and a sugar, wherein the aforementioned base includes at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

[0036] In this specification, nucleic acid refers to a structure consisting of a base and a sugar, and is sometimes described as a nucleic acid that "contains only bases".

[0037] The aforementioned nucleic acid class is preferably comprised of at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids, wherein at least one of the aforementioned nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids has a structure formed by the combination of a base and a sugar, and wherein the aforementioned base comprises at least one selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine. The nucleotide is further preferably comprised of ribonucleotides or deoxyribonucleotides, and more preferably ribonucleotides.

[0038] Among nucleic acids, those containing purine bases can be interconverted or decomposed to serve as common raw materials for biosynthesis. In addition, among nucleic acids, those containing pyrimidine bases can be interconverted or decomposed to serve as common raw materials for biosynthesis.

[0039] From this perspective, it is preferable that the nucleic acids contained in the eel fry feed of the embodiment have a structure formed by the combination of bases and sugars, and the aforementioned bases include purine bases and pyrimidine bases.

[0040] The types of bases contained in nucleic acids are considered in relation to the nucleic acids contained in the feed for eel fry in the implementation form. For example, when the aforementioned nucleic acids are nucleosides or nucleotides, the purine bases and pyrimidine bases contained in the nucleic acids in the feed for eel fry in the actual form can be contained in different nucleic acid molecules. For example, when the aforementioned nucleic acids are polynucleotides, the purine bases and pyrimidine bases contained in the nucleic acids in the feed for eel fry in the embodiment can be contained in different nucleic acid molecules, or they can be contained in the same nucleic acid molecule as usual, such as DNA and RNA.

[0041] Among the bases exemplified above, examples of purine bases include adenine, guanine, and hypoxanthine. Among the bases exemplified above, examples of pyrimidine bases include thymine, uracil, and cytosine.

[0042] The nucleic acids contained in the feed for eel fry in the implementation form are preferably those with a structure formed by the combination of bases and sugars, wherein the aforementioned 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.

[0043] Furthermore, the nucleic acids contained in the eel larvae feed of the embodiment are preferably at least one selected from the group consisting of ribonucleosides, deoxyribonucleosides, ribonucleotides, deoxyribonucleotides, ribonucleic acid and deoxyribonucleic acid, and salts of these nucleic acids. The aforementioned ribonucleosides, deoxyribonucleosides, ribonucleotides, deoxyribonucleotides, ribonucleic acid and deoxyribonucleic acid, and salts of these nucleic acids have a structure formed by the combination of a base and a sugar. The aforementioned 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.

[0044] From the perspective of making more efficient use of eel larvae, nucleic acids are preferably those containing various bases. The aforementioned nucleic acids preferably have a structure formed by the combination of bases and sugars, wherein the aforementioned bases include adenine and / or hypoxanthine, guanine, thymine and / or uracil, and cytosine. The aforementioned nucleic acids are preferably those with a structure formed by the combination of bases and sugars, wherein the aforementioned bases include adenine and / or hypoxanthine, guanine, uracil, and cytosine.

[0045] The aforementioned nucleic acid class is preferably comprised of at least one selected from the group consisting of ribonucleosides, ribonucleotides, and ribonucleic acids, and salts of these nucleic acids, wherein the aforementioned ribonucleosides, ribonucleotides, and ribonucleic acids, and salts of these nucleic acids, have a structure formed by the combination of a base and a sugar, wherein the aforementioned bases include adenine and / or hypoxanthine, guanine, uracil, and cytosine.

[0046] 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, eel larvae likely synthesize fewer nucleic acids and must obtain them from their food, but previous diets may not have adequately met their nucleic acid requirements. In particular, it is believed that during the metamorphosis from willow eel to glass eel, there is a high probability of significant gene expression and cell division accompanying morphological changes. Feeding them with nucleic acid-containing diets can help these gene expression and cell division processes proceed smoothly.

[0047] In the feed for eel larvae of the implementation form, the content of the aforementioned nucleic acids relative to the total dry weight (100% by weight) of the aforementioned feed for eel larvae may exceed 0.04% by weight, or be 0.05% by weight or more, or 0.07% by weight or more, or 0.1% by weight or more, or 0.15% by weight or more, or 0.2% by weight or more, or 0.25% by weight or more, or 0.5% by weight or more, or 0.8% by weight or more, or 0.9% by weight or more, or 1.0% by weight or more, or 1.5% by weight or more, or 2.0% by weight or more, or 2.5% by weight or more, or 3.0% by weight or more, or 3.5% by weight or more, or 3.8% by weight or more, or 3.9% by weight or more.

[0048] By converting the total dry weight (100% by weight) to a dry weight value, eel larvae feed containing nucleic acids exceeding or above the aforementioned lower limit can more effectively reduce the frequency of morphologically abnormal individuals during the metamorphosis of eel larvae into glass eels.

[0049] In the feed for eel larvae of the implementation form, the content of the aforementioned nucleic acids relative to the total dry weight (100% by weight) of the aforementioned feed for eel larvae 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.

[0050] By converting the total dry weight (100% by weight) to the dry weight of eel larvae feed containing the aforementioned nucleic acids below the upper limit, eel larvae can grow better.

[0051] As one example of the aforementioned numerical range of nucleic acids contained in the eel larvae feed of the embodiment, the content of the aforementioned nucleic acids in the eel larvae feed of the embodiment, relative to the total dry weight (100% by weight) of the aforementioned eel larvae feed, may be more than 0.04% by weight and less than 20% by weight, more than 0.05% by weight and less than 20% by weight, more than 0.07% by weight and less than 15% by weight, more than 0.1% by weight and less than 15% by weight, more than 0.15% by weight and less than 10% by weight, more than 0.2% by weight and less than 10% by weight, and less than 0.25% by weight. % to less than 10% by weight, may be 0.5% to less than 9% by weight, may be 0.8% to less than 9% by weight, may be 0.9% to less than 8% by weight, may be 1.0% to less than 8% by weight, may be 1.5% to less than 7% by weight, may be 2.0% to less than 7% by weight, may be 2.5% to less than 6% by weight, may be 3.0% to less than 6% by weight, may be 3.5% to less than 5% by weight, may be 3.8% to less than 5% by weight, may be 3.9% to less than 5% by weight.

[0052] The dry weight of feed or feed ingredients for larvae can be determined by drying the feed or feed ingredients at 105°C for 6 hours.

[0053] The content of nucleic acids in feed for eel larvae can be determined using known analytical methods. High-performance liquid chromatography (HPLC) can be used as an analytical method. For example, feed or feed ingredients, or processed products thereof, can be used as the test sample to determine the content of various nucleic acids. The test sample can be processed according to the type of nucleic acid being tested. For example, the feed or feed ingredients can be subjected to perchloric acid extraction or nuclease treatment.

[0054] The preferred form of eel larvae feed contains yeast extract. The yeast extract may contain the aforementioned nucleic acids. Yeast extract is also known as yeast extract. The preferred form of eel larvae feed may contain nucleic acids and / or yeast extract.

[0055] The content of the aforementioned yeast extract relative to the total dry weight (100% by weight) of the aforementioned eel fry feed may be more than 1% by weight, more than 1% by weight to less than 50% by weight, more than 5% by weight to less than 40% by weight, or more than 10% by weight to less than 30% by weight.

[0056] Furthermore, the numerical values ​​of the nucleic acid content exemplified above in the eel fry feed as an embodiment (the numerical values ​​exemplified in the range of more than 0.04% by weight and less than 20% by weight relative to the total dry weight (100% by weight) of the eel fry feed) can also be referred to as the numerical values ​​of the nucleic acid content derived from yeast extract.

[0057] In terms of better raising eel fry, it is better to use feed for eel fry that contains milk protein.

[0058] In this specification, "milk protein" refers to proteins derived from milk. Milk protein is one of the proteins that can be obtained inexpensively and reliably, and various products made from cow's milk are available on the market. Specifically, examples include skim milk powder and various caseins made from cow's milk.

[0059] The aforementioned milk protein content, relative to the total dry weight (100% by weight) of the aforementioned eel fry feed, may be 10% or more by weight, 10% or more to 80% or less by weight, 20% or more to 60% or less by weight, or 30% or more to 50% or less by weight.

[0060] The feed for eel larvae may further include protein sources other than milk protein. Preferably, the protein source is bird egg components or chicken egg components, and for ease of acquisition, egg yolk powder is preferred.

[0061] The content of the aforementioned egg component relative to the total dry weight (100% by weight) of the aforementioned eel fry feed may be more than 5% by weight, more than 5% by weight but less than 30% by weight, more than 7% by weight but less than 25% by weight, or more than 10% by weight but less than 20% by weight.

[0062] As an example of an implementation of eel larvae feed, an example of an eel larvae feed is provided, which contains nucleic acids, milk protein, and egg components (e.g., egg yolk powder). Relative to the total dry weight of the aforementioned eel larvae feed, the content of the aforementioned nucleic acids is 0.25% to 10% by weight, the content of the aforementioned milk protein is 10% to 80% by weight, and the content of the aforementioned egg components is 5% to 30% by weight.

[0063] As an example of an implementation of eel larvae feed, the following eel larvae feed is provided, which contains nucleic acids, yeast extract, milk protein, and egg components (e.g., egg yolk powder). The aforementioned yeast extract contains the aforementioned nucleic acids. Relative to the total dry weight of the aforementioned eel larvae feed, the content of the aforementioned yeast extract is 1% to 50% by weight, the content of the aforementioned milk protein is 10% to 80% by weight, and the content of the aforementioned egg components is 5% to 30% by weight.

[0064] Besides milk protein, fishmeal is another protein source that can be cited. From the perspective of improving digestibility and absorption, enzyme-treated fishmeal is preferred. Enzyme-treated fishmeal can be made from the flesh of any type of fish, such as fishmeal treated with peptidases, proteases, or proteolytic enzymes.

[0065] The optimal blending ratio of milk protein to other proteins is such that the lactose content is less than 10% by weight of the total dry weight of the eel larvae feed. If low-lactose milk protein or casein is used, the amount of milk protein in the blend can be increased.

[0066] As one embodiment of eel larvae feed, examples include eel larvae feed containing nucleic acids and / or yeast extracts, as well as milk proteins.

[0067] As another embodiment of eel fry feed, examples include eel fry feed containing nucleic acids and / or yeast extracts, milk protein, and egg yolk powder.

[0068] As another embodiment of eel larvae feed, examples include eel larvae feed containing nucleic acids and / or yeast extracts, milk protein, egg yolk powder, and fish meal.

[0069] Furthermore, in terms of improving the growth or survival rate of eel larvae, it is preferable that the feed for eel larvae contains vitamins. Examples of vitamins include vitamin C, vitamin A, vitamin E, vitamin B1, vitamin B2, vitamin B6, vitamin B12, vitamin D, vitamin K, nicotinic acid, pantothenic acid, folic acid, biotin, etc., and may also include choline, inositol, etc.

[0070] In addition, in terms of improving growth or survival rates, it is preferable for eel fry feed to contain taurine.

[0071] As another embodiment, eel larvae feed may include eel larvae feed containing nucleic acids and / or yeast extracts, milk protein, egg yolk powder, fish meal, vitamins, and taurine.

[0072] In addition, it is generally preferable to provide eel larvae with n-3 highly unsaturated fatty acids such as EPA (eicosapentaenoic acid) or DHA (docosahexaenoic acid). Therefore, the preferred form of eel larvae feed is fish oil such as liver oil containing the above-mentioned n-3 highly unsaturated fatty acids.

[0073] The feed for eel fry in the implementation form may contain soybean peptides (preferably soybean peptides with reduced phytic acid treatment) as other arbitrary ingredients.

[0074] The eel larvae feed of the embodiment can be, for example, made by further adding nucleic acids and / or yeast extracts to any basic eel larvae feed. Here, the basic eel larvae feed refers to feed that enables eel larvae to grow and metamorphose into eel juveniles, such as the eel larvae feed described in Patent Document 2 or Patent Document 3. As for the amount of nucleic acids and / or yeast extracts added, it can be set to satisfy the above-described amount of the aforementioned nucleic acid content relative to the total dry weight of the aforementioned eel larvae feed.

[0075] 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 this embodiment is preferably free of shark egg components. In this specification, "shark egg components" refers to components derived from shark eggs. Shark eggs can be exemplified by white-spotted dogfish eggs.

[0076] The form of eel fry feed can be powder, or, for ease of distribution and storage, dry powder. Alternatively, to facilitate swallowing by the fry, water or seawater can be added to the powdered eel fry feed to obtain a paste-like eel fry feed before feeding.

[0077] By feeding larvae with morphologically modified larvae feed, the frequency of individuals exhibiting morphological abnormalities during the metamorphosis from larvae to glass eels can be reduced.

[0078] In this specification, morphological abnormalities refer to severe deformities of the spine, such as curvature, undulation, bending, and decapitation (see Figure 2). Severe deformities are those whose degree of abnormality can be determined by the observer using an optical microscope.

[0079] The rate of morphological abnormalities in the produced eel fry, based on the quantitative benchmark of observations of more than 16 individuals, may be less than 35%, less than 30%, less than 25%, less than 20%, less than 15%, or less than 10%.

[0080] <Method for manufacturing feed for eel fry> The method for manufacturing feed for eel larvae includes the following steps: mixing various raw materials or raw material components at one time or in an appropriate order to obtain feed for eel larvae in the embodiment.

[0081] By means of manufacturing feed for larvae in the actual form, feed for larvae in the actual form can be manufactured.

[0082] The various raw materials or raw material components, and their contents, can be listed as those exemplified in the above-mentioned "Feed for Eel Fry". Besides nucleic acids, other raw materials or raw material components include yeast extract, milk protein, egg yolk powder, fish meal, vitamins, taurine, fish liver oil, and any other ingredients listed above. Water or seawater may also be appropriately added to the feed for eel fry.

[0083] As an example of a method for manufacturing feed for eel larvae, a method for manufacturing feed for eel larvae including the following steps is shown: the aforementioned nucleic acid and / or yeast extract are formulated such that they contain 0.25% by weight or more of nucleic acids by dry weight relative to the total dry weight (100% by weight) of the aforementioned feed for eel larvae.

[0084] As an example of a method for manufacturing feed for eel larvae, a method for manufacturing feed for eel larvae including the following steps is shown: the aforementioned nucleic acid and / or yeast extract are formulated such that they contain no more than 10% by weight of nucleic acid relative to the total dry weight (100% by weight) of the aforementioned feed for eel larvae.

[0085] As an example of a method for manufacturing feed for eel larvae, a method for manufacturing feed for eel larvae including the following steps is shown: the aforementioned nucleic acid and / or yeast extract are formulated in such a way that the total dry weight (100% by weight) of the aforementioned feed for eel larvae contains 0.25% to 10% by weight of nucleic acid on a dry weight basis.

[0086] For example, the feed for eel larvae can also be manufactured by adding nucleic acids and / or yeast extracts to any basic eel larvae feed. Here, the basic eel larvae feed refers to feed that can induce eel larvae to metamorphose into eel juveniles. The amount of nucleic acid and / or yeast extract added can be exemplified as the amount of the aforementioned nucleic acid content relative to the total dry weight of the aforementioned eel larvae feed, as shown above.

[0087] For example, an eel fry feed can be prepared by mixing 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) used for feed preparation.

[0088] In one embodiment, the present invention provides a use of nucleic acids for manufacturing feed for eel fry. In one embodiment, the present invention provides a use of yeast extract for manufacturing feed for eel fry.

[0089] Methods of Eel Production The method for producing eels in this embodiment includes feeding eel larvae with feed for eel larvae.

[0090] In addition, as one embodiment, a method is provided to reduce the frequency of occurrence of glass eel individuals exhibiting morphological abnormalities, which includes feeding eel larvae with eel larvae feed as described in the embodiment.

[0091] As an example of eel larvae feed, the examples listed in the above-mentioned "Eel Larvae Feed" can be cited.

[0092] There are no particular restrictions on the method of raising eel fry, and it can be carried out according to the well-known methods of raising eel fry. As an example, eel fry can be raised in water at a temperature of 23 to 25 degrees Celsius and a salinity concentration of 16 to 34 psu (practical salinity unit).

[0093] There are no particular restrictions on the method of feeding eel fry; they can be fed according to the usual methods for raising eel fry. The feeding frequency for eel fry can be more than once a day, for example, three to five times a day (preferably with a feeding interval of at least two hours). The amount of eel fry feed should be adjusted appropriately based on the feeding status of the eel fry; it is best to feed them when they are full.

[0094] The feeding period for eel larvae in the metamorphosis process is not particularly limited as long as it is during 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. For example, feeding eel larvae in the metamorphosis process with eel larvae feed at least once a day during the period from 10 days prior to the start of metamorphosis to the end of metamorphosis, more preferably from 30 days prior to the start of metamorphosis to the end of metamorphosis, and even more preferably from 60 days prior to the start of metamorphosis to the end of metamorphosis. The feeding period for eel larvae in the metamorphosis process can be continuous or discontinuous, for example, it can be more than 10 days, more than 50 days, more than 100 days, or more than 150 days.

[0095] Furthermore, metamorphosis can also be induced by appropriately setting a period during which eel fry are kept without feeding them before metamorphosis begins.

[0096] The preferred method for producing larvae of the implementation form is the production of artificial seedlings, which includes feeding larvae of the implementation form with feed. The artificial breeding here refers to the production of eel fry that are artificially spawned and hatched, growing them into glass eels.

[0097] The production method for eels in the implementation form can be set as complete aquaculture. Complete aquaculture involves artificially spawning and hatching eels and raising them to adulthood, from which the eggs laid by the adult eels are used to raise the next generation of adult eels.

[0098] Inhibitor of Morphological Abnormalities in Eel Juveniles The inhibitor for abnormal morphology in eel juveniles contains nucleic acids as its active ingredient. The inhibitor for abnormal morphology in eel juveniles may contain yeast extract as an active ingredient.

[0099] Nucleic acid compounds and yeast extracts contained in eel fry morphological abnormalities can be listed in the above-mentioned "Feed for Eel Fry".

[0100] By adding an inhibitor of morphological abnormalities in juvenile eels to any eel feed, preferably to larval eel feed and feeding it to larvae, the frequency of occurrence of glass eel individuals exhibiting morphological abnormalities can be reduced.

[0101] In one embodiment, the present invention provides a use of nucleic acids as an inhibitor of morphological abnormalities in juvenile eels. In one embodiment, the present invention provides a use of yeast extract as an inhibitor of morphological abnormalities in juvenile eels.

[0102] The eel larvae feed, eel production method, and eel juvenile morphology abnormality inhibitor described above enable the artificial rearing of eel larvae using a stable supply of raw materials, and the production of high-quality glass eels. This embodiment of the eel larvae feed, eel production method, and eel juvenile morphology abnormality inhibitor is extremely useful in realizing the long-desired commercialization of complete eel farming and large-scale production. [Example]

[0103] The following embodiments further illustrate the invention in detail, but the invention is not limited to the following embodiments.

[0104] [Experiment 1] Evaluation of the effect of adding nucleic acids to feed on the frequency of morphological abnormalities Feed ingredients) • Dried egg yolk powder (manufactured by Kewpie Egg Co., Ltd., Dried Egg Yolk No. 1) • Enzyme-treated fishmeal (manufactured by Scientific Feed Research Institute Co., Ltd., CPSP SPECIAL G) • Casein Sodium (manufactured by Nippon Shinyaku Co., Ltd., sodium casein LW) • Skim milk powder (manufactured by Yotsuba Milk Products Co., Ltd., Hokkaido skim milk powder) • Soybean peptides (manufactured by Nippon Pharmaceutical Co., Ltd., HIPOLYPEPTON N) • Yeast Extract (High IMP) (Manufactured by KOHJIN Life Sciences Co., Ltd., Aromild (registered trademark)) • Nucleic acid mixtures (made by mixing disodium salts of AMP, IMP, GMP, CMP, and UMP in equal weights) AMP: Adenosine 5'-monophosphate disodium salt (FUJIFILM Wako QB-7150) IMP: Inosine 5'-monophosphate disodium salt (NACALAI TESQUE 06400-22) GMP: Disodium 5'-guanine monophosphate salt (Fujifilm Wako QB-3304) CMP: Cytidine 5'-monophosphate disodium salt (Tokyo Kasei C0524) UMP: Uridine 5'-monophosphate disodium salt (Fujifilm Wako QR-1512) • Taurine (manufactured by NACALAI TESQUE Co., Ltd., reagent taurine) • Vitamin Mixture (Manufactured by NUTRITION Co., Ltd., Japan; for fisheries research and educational institutions) • Cod liver oil (manufactured by Kanematsu Shin-A Food Co., Ltd., Hicarol E)

[0105] method) Five-day-old eel fry were housed in 12 rearing tanks (acrylic bowl-shaped tanks, approximately 10L in volume) at a density of 500 fry per tank. Six-day-old eel fry were fed shark roe substitute feed (FSD, as shown in Table 1, a modified version of the fishmeal feed described in Table 1 of Patent Document 3), and were pre-raised until 80 days of age. Feeding was conducted five times a day (at 2-hour intervals), with a feed volume of 7-10 mL per feeding. The water temperature was set at 23°C, and the water flow rate was 0.5-0.7 L / min. Tank replacement was performed after the final feeding of the day. Eighty-day-old fry were collected and redistributed into 12 rearing tanks at a rate of 80 fry per tank. The feed ingredients were mixed according to the composition (g) shown in Table 1 to prepare the experimental feeds. After 81 days of age, experimental zones were established to provide the feeds shown in Table 1. A total of six experimental zones were established: a control zone fed with FSD (FSD zone); a zone fed with FSD supplemented with 0.5g, 1.0g, 2.0g, or 4.0g of nucleic acid mixture (FSD+NM zone); and a zone fed with FSD supplemented with yeast extract and altered proportions of some ingredients (FSY zone). Each experimental zone consisted of two tanks. Basic rearing conditions were the same as those until 80 days of age. After feeding until 340 days of age, the fry were then reared without feeding from 341 days of age onwards to induce metamorphosis. Individuals exhibiting signs of metamorphosis (such as forward shift of the anus and decreased body height) were removed from their rearing tanks and individually placed in 250mL polycarbonate containers filled with water. They were kept unfed and the metamorphosis process was observed. The point at which the body shape completely transformed into that of a glass eel was defined as the completion of metamorphosis. After anesthesia, photographs were taken to record the body shape at the time of metamorphosis completion as visual data. The morphological abnormality was determined by defining individuals with severe spinal deformities as abnormal, and the assessment was conducted independently by two skilled assessors. Individuals whose assessments differed were consolidated. An example of an individual assessed as "no morphological abnormality" or "with morphological abnormality" is shown in Figure 2. To verify the effect of nucleic acid mixtures or yeast extracts added to feed on the frequency of morphological abnormalities, binary data related to the presence or absence of morphological abnormalities at the completion of metamorphosis were set as the target variable, and the type of feed (experimental area) was set as the explanatory variable. Logistic regression analysis was used to calculate the odds ratio and 95% reliability interval of different feeds against the occurrence of morphological abnormalities.

[0106] [Table 1] Raw materials (g) pilot zone FSD FSD+NM0.5 FSD+NM1.0 FSD+NM2.0 FSD+NM4.0 FSY dried egg yolk powder 15 15 15 15 15 10 Enzyme-treated fishmeal 30 30 30 30 30 30 Casein Na 20 20 20 20 20 20 skim milk powder 15 15 15 15 15 10 Soybean peptides 5 5 5 5 5 - Yeast extract (high IMP) - - - - - 15 Nucleic acid mixtures - 0.5 1 2 4 - Taurine 2 2 2 2 2 2 Vitamin Mixture 2 2 2 2 2 2 Cod liver oil 5 5 5 5 5 4 Total (g) 94 94.5 95 96 98 93 Total dry weight (g) 90.9 91.4 91.9 92.9 94.9 90.0 Nucleic acid content (weight %)* 0.04 0.52 0.99 1.93 3.74 4.00 *Calculated from the amount of nucleic acid mixture added, total nucleotides and total nucleosides in yeast extract (analytical value), and the amount of nucleic acids derived from the raw materials (analytical value).

[0107] In Experiments 1 to 3, the descriptions of "-" in Tables 1, 3 and 6 indicate that the raw material is not prepared. In Experiments 1 to 3, the total dry weight is defined as the sum of the values ​​of the feed ingredients after drying by heating at 105°C for 6 hours. When using nucleic acids as disodium salts, the amount of nucleic acid is expressed as 0.88 times the amount used, excluding the disodium portion.

[0108] The "Nucleic Acid Content (weight %)" item in the table indicates the proportion (weight %) of nucleic acid content relative to the total dry weight of the feed.

[0109] result) The number of individuals beginning metamorphosis appeared at 138 days of age, and by 340 days of age, the cumulative number of individuals beginning metamorphosis was 308 (FSD area: 29, FSD+NM0.5 area: 48, FSD+NM1.0 area: 52, FSD+NM2.0 area: 65, FSD+NM4.0 area: 54, FSY area: 60). The number of individuals that completed metamorphosis was 283 (FSD area: 27, FSD+NM0.5 area: 43, FSD+NM1.0 area: 50, FSD+NM2.0 area: 57, FSD+NM4.0 area: 49, FSY area: 57). The incidence and odds ratio of morphological abnormalities in each experimental area are shown in Figure 3 and Table 2. Compared to the control FSD area, in the four experimental areas with added nucleic acid mixtures, the higher the concentration of the added nucleic acid mixture, the lower the odds ratio for morphological abnormalities, with the greatest reduction in the FSY area. Setting the incidence frequency in the FSD areas, estimated by the odds ratio, as 100%, the reduction rate was 50.0% in the FSD+NM0.5 area, 63.6% in the FSD+NM1.0 area, 69.1% in the FSD+NM2.0 area, 75.8% in the FSD+NM4.0 area, and 94.7% in the FSY area, indicating that the addition of nucleic acid mixtures or yeast extracts can reduce the incidence of morphological abnormalities. The proportion of individuals exhibiting morphological abnormalities decreased in a dependent manner with the content of nucleic acids in the feed.

[0110] [Table 2] Types of feed Nucleic acid content (weight%) There are morphological abnormalities No morphological abnormalities odds ratio* (95% reliability interval) Frequency of morphological abnormalities FSD 0.04 11 (40.7%) 16 (59.3%) Reference 100% FSD+NM0.5 0.52 11 (25.6%) 32 (74.4%) 0.500 (0.179, 1.399) -50.0% FSD+NM1.0 0.99 10 (20.0%) 40 (80.0%) 0.364 (0.129, 1.023) -63.6% FSD+NM2.0 1.93 10 (17.5%) 47 (82.5%) 0.309 (0.111, 0.864) -69.1% FSD+NM4.0 3.74 7 (14.3%) 42 (85.7%) 0.242 (0.080, 0.735) -75.8% FSY 4.00 2 (3.5%) 55 (96.5%) 0.053 (0.011, 0.234) -94.7% *The lower the odds ratio, the lower the probability of developing severe spinal abnormalities relative to FSD. Significant differences exist when the 95% reliability interval is below 1.

[0111] [Experiment 2] Study of various yeast extracts Feed ingredients that are not common to those in Experiment 1 above • Yeast Extract (High AMP) (Manufactured by Hsing Jen Life Science Co., Ltd., NUCLEAMINE (Registered Trademark)) • Yeast extract (reagent) (manufactured by Sigma-Aldrich, yeast extract 09182)

[0112] method) Six-day-old eel larvae were housed in 14 rearing tanks (U-shaped polycarbonate tanks, approximately 30L in volume) at a density of 1,000 to 1,500 larvae per tank. Shark eggs were fed to the 6-day-old eel larvae as a substitute for fecal micrograss (FSD), and they were pre-reared until 39 days of age. Feeding was conducted five times a day (at 2.5-hour intervals), 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. Tank replacement was performed after the final feeding of the day. Forty-day-old fry were collected and redistributed into 14 30L U-shaped tanks at a rate of 400 fry per tank. The feed ingredients were mixed according to the composition (g) shown in Table 3 to prepare the experimental feeds. After 40 days of age, experimental zones were established, providing all four experimental feeds shown in Table 3. Each experimental zone consisted of either three or four tanks (FSD zone: 4, FSY2 zone: 4, FSX zone: 3, FSZ zone: 3). Basic rearing conditions were the same as those until 39 days of age, and the fry were fed until 304 days of age. From 305 to 330 days of age, the fry were reared without feeding to induce metamorphosis. The definitions of the onset and completion of metamorphosis, the methods for recording phenotypes, the identification of morphological abnormalities, and the statistical analysis were set to be the same as in Experiment 1.

[0113] [Table 3] Raw materials (g) pilot zone FSD FSY2 FSX FSZ dried egg yolk powder 15 10 10 10 Enzyme-treated fishmeal 30 30 30 30 Casein Na 20 20 20 20 skim milk powder 15 15 15 15 Soybean peptides 5 - - - Yeast extract (high IMP) - 14 - - Yeast extract (high AMP) - - 14 - Yeast extract (reagent) - - - 14 Taurine 2 1.5 1.5 1.5 Vitamin Mixture 2 2 2 2 Cod liver oil 5 3 3 3 Total (g) 94 95.5 95.5 95.5 Total dry weight (g) 90.9 92.4 92.4 92.3 Nucleic acid content (weight %)* 0.04 3.64 3.96 0.84 *Calculated from the total nucleotides and total nucleosides (analytical values) in each yeast extract and the amount of nucleic acids derived from the raw materials (analytical values).

[0114] result) The content of nucleotides in the feed FSD and the three added yeast extracts was analyzed. The analysis was performed on samples extracted with 5% perchloric acid to determine the content of various nucleic acids. 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 using 5'-inosine as the target, samples extracted with 5% perchloric acid were analyzed to determine the content). Furthermore, the primary source of nucleic acids in yeast extracts (Aromild and NUCLEAMINE, manufactured by Hsing Jen Life Science Co., Ltd.) is RNA. During the manufacturing process, RNA is broken down, therefore, the nucleic acids in the yeast extract exist in the form of nucleotides. Regarding reagent yeast extract (manufactured by Sigma-Aldrich), no nucleotides were detected in feed that had not undergone enzymatic breakdown by nuclease P1. Therefore, the nucleic acids in the reagent yeast extract are contained in the form of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

[0115] The analytical results of the nucleotides contained in the feed FSD and the three yeast extracts used are presented in Table 4 as the content (weight %) per dry weight of feed FSD or yeast extract. The total nucleotides and total nucleosides of the analytical values ​​are used as the nucleic acid content. The feed FSD contained almost no nucleic acids, and the analytical items other than those specified in GMP were below the detection limit (0.01g / 100g). Aromild contained IMP, UMP, GMP, and CMP, with a total nucleotide content of 23.05% by weight and a total nucleoside content of 1.44% by weight. NUCLEAMINE contained AMP, UMP, GMP, and CMP, with a total nucleotide content of 24.86% by weight and a total nucleoside content of 1.74% by weight. The reagent yeast extract contained AMP, UMP, GMP, and CMP, with a total nucleotide content of 4.24% by weight and a total nucleoside content of 1.22% by weight. Furthermore, in the region below the detection limit of 5'-thymidine, the levels of deoxynucleotides, deoxyribonucleotides, and DNA are presumed to be below the detection limit.

[0116] [Table 4] FSD FSY2 FSX FSZ Aromild NUCLEAMINE reagent yeast extract Xingren Life Science Xingren Life Science Sigma Oric Analysis items (by weight %) 5'-Adenosine Unable to detect Unable to detect 7.07 0.95 5'-inosine Unable to detect 6.69 Unable to detect Unable to detect 5'-uridine monophosphate Unable to detect 5.49 6.03 1.12 5'-Guanyu acid 0.04 6.33 6.85 1.23 5'-cytidine Unable to detect 4.54 4.91 0.93 5'-thymidine acid Unable to detect Unable to detect Unable to detect - Total nucleotides 0.04 23.05 24.86 4.24

[0117] The total number of tails that began metamorphosis by the end of the breeding period was 163 (FSD area: 18 tails, FSY2 area: 59 tails, FSX area: 64 tails, FSZ area: 22 tails), and the total number of tails that completed metamorphosis was 138 (FSD area: 16 tails, FSY2 area: 46 tails, FSX area: 59 tails, FSZ area: 17 tails). The incidence and odds ratio of morphological abnormalities in each experimental area are shown in Figure 4 and Table 5. Compared with the feed-free controlled (FSD) areas, the odds ratio for morphological abnormalities was lower in the three experimental areas with added yeast extract. When the incidence rate in the FSD areas, estimated by the odds ratio, was set at 100%, the reduction rate was 68.6% in FSY2, 96.5% in FSX, and 58.3% in FSZ, indicating that the addition of yeast extract containing nucleic acids can reduce the incidence of morphological abnormalities.

[0118] [Table 5] Types of feed Types of yeast extracts Nucleic acid content (by weight %) There are morphological abnormalities No morphological abnormalities odds ratio* (95% reliability interval) Frequency of morphological abnormalities FSD No additives 0.04 8 (50.0%) 8 (50.0%) Reference 100% FSY2 Aromild 3.64 11 (23.9%) 35 (76.1%) 0.314 (0.095, 1.034) -68.6% FSX NUCLEAMINE 3.96 2 (3.4%) 57 (96.6%) 0.035 (0.006, 0.195) -96.5% FSZ reagent yeast extract 0.84 5 (29.4%) 12 (70.6%) 0.417 (0.100, 1.743) -58.3% *The lower the odds ratio, the lower the probability of developing a severe spinal abnormality relative to FSD. Significant differences exist when the 95% reliability interval is below 1.

[0119] [Experiment 3] Study on the content of nucleic acids in feed Feed ingredients that are not common to those in Experiments 1 to 2 above. • Nucleic acid mixture (manufactured by Marugo Corporation, a mixture of sodium 5'-ribonucleotide nucleic acid, IMP, and GMP) • Vitamin mixtures (see Furuita et al. (2014) Fisheries Science, 80, 581-587) Taurine (manufactured by Fujifilm and Kamitsu Chemical Co., Ltd.)

[0120] method) Six-day-old eel larvae were housed in seven rearing tanks (acrylic bowl-shaped tanks, approximately 10L in volume) at a density of 250 larvae per tank. The feed ingredients were mixed according to the composition (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 frequency was five times a day (at 2-hour intervals), with a feed volume of 7 mL per feeding. The water temperature was 23°C, and the water flow rate was 0.4 L / min to 0.6 L / min. Tank replacement was performed after the last feeding of the day. Seven experimental zones were established, each containing one tank of feed containing 1g, 2g, 5g, 10g, 15g, or 20g of a nucleic acid mixture (a mixture of IMP and GMP) added to the feed (FSD). At 20 days of age, 31 to 33 fish were randomly collected from each tank. After anesthesia, photographs were taken under a stereomicroscope, and ImageJ was used for image analysis to determine total length and body height. The relationship between the 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, by weight%) in each experimental area was plotted as an S-shaped curve, which was estimated to be the inflection point of the maximum response at 50%.

[0121] [Table 6] Raw materials (g) pilot zone FSD 3-1 3-2 3-3 3-4 3-5 3-6 dried egg yolk powder 15 15 15 15 15 15 15 Enzyme-treated fishmeal 30 30 30 30 30 30 30 Casein Na 20 20 20 20 20 20 20 skim milk powder 15 15 15 15 15 15 15 Soybean peptides 5 5 5 5 5 5 5 Nucleic acid mixtures (IMP, GMP) - 1 2 5 10 15 20 Taurine 2 2 2 2 2 2 2 Vitamin Mixture 1 1 1 1 1 1 1 Cod liver oil 5 5 5 5 5 5 5 Total (g) 93 94 95 98 103 108 113 Total dry weight (g) 89.9 90.8 91.6 94.1 98.2 102.4 106.5 Nucleic acid content (weight %)* 0.04 0.95 1.84 4.44 8.46 12.17 15.58 *Calculated from the amount of nucleic acid mixture added and the amount of nucleic acids derived from the raw materials (analytical value).

[0122] result) Figure 5 shows the relationship between the average total length and average body height of 20-day-old eel larvae and the nucleic acid content of their diet. The inflection points and 95% confidence intervals for each parameter were estimated to be 9.99 (7.7 to 12.3) and 9.79 (7.8 to 11.8), respectively. This indicates that, for example, feeding eel larvae with a diet containing less than 10% by weight of nucleic acids per dry weight can achieve better growth.

[0123] Each embodiment and its combination is an example, and additions, omissions, substitutions, and other changes to the composition can be made without departing from the spirit of the invention. Furthermore, the invention is not limited to each embodiment, but is limited only by the scope of the claims (patent claims). [Industrial Applicability]

[0124] 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, thus enabling industrial application.

Claims

1. A feed for eel fry used to inhibit abnormal morphology in eel fry, comprising nucleic acids; wherein the content of the aforementioned nucleic acids is 0.25% by weight or more relative to the total dry weight of the aforementioned feed for eel fry used to inhibit abnormal morphology in eel fry.

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

3. The eel fry feed for inhibiting abnormal morphology in eel fry as described in claim 1 or 2, wherein the aforementioned nucleic acid class includes at least one selected from the group consisting of nucleosides, nucleotides, polynucleotides, and salts of these nucleic acids.

4. The eel fry feed for inhibiting abnormal morphology in eel fry as described in claim 1 or 2, wherein the aforementioned nucleic acid has a structure formed by the combination of a base and a sugar; the aforementioned base includes at least one base selected from the group consisting of adenine, guanine, thymine, uracil, cytosine, and hypoxanthine.

5. The eel fry feed for inhibiting abnormal morphology in eel fry as described in claim 1 or 2, wherein the aforementioned nucleic acids have a structure formed by the combination of bases and sugars; the aforementioned bases include purine bases and pyrimidine bases.

6. The eel fry feed for inhibiting morphological abnormalities in eel fry as described in claim 1 or 2, wherein the eel fry feed for inhibiting morphological abnormalities in eel fry contains yeast extract, and the yeast extract contains the aforementioned nucleic acids.

7. The eel fry feed for inhibiting abnormal morphology in eel fry as described in claim 1 or 2, wherein the aforementioned eel fry feed for inhibiting abnormal morphology in eel fry does not contain shark egg components.

8. The eel fry feed for inhibiting morphological abnormalities in eel fry as described in claim 1 or 2, wherein the aforementioned eel fry feed for inhibiting morphological abnormalities in eel fry further comprises milk protein.

9. The eel fry feed for inhibiting abnormal morphology in eel fry as described in claim 1 or 2, wherein the aforementioned eel fry feed for inhibiting abnormal morphology in eel fry further comprises an egg component.

10. A method for producing eels, comprising feeding eel fry with feed for inhibiting morphological abnormalities in eel fry as described in claim 1 or 2.

11. The eel production method as described in claim 10, wherein the aforementioned feeding is satiated feeding.

12. The eel production method described in claim 10 is for the production of artificial seedlings.

13. An inhibitor of abnormal morphology in eel fry, comprising nucleic acids as an active ingredient; the aforementioned inhibitor of abnormal morphology in eel fry is used to: add to feed for eel larvae to manufacture feed for eel larvae as described in any one of claims 1 to 9 for inhibiting abnormal morphology in eel fry.

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