Method for inducing eel feminization, eel rearing method, eel feminization agent, and feed for eels

Abstract

[Task] To provide a means to induce feminization in eels with high efficiency and with fewer concerns regarding safety and the environment. [Solution] A method for inducing eel feminization is provided by feeding eel feed containing 0.05% by weight or more of soybean isoflavones in the dry matter during the stage of eel fry and / or small eel. By feeding the eel feed during a predetermined period while the eel is growing from an eel fry to a small eel, eel feminization can be reliably induced with high efficiency, and compared to cases where eel feminization is induced using estradiol 17β, etc., concerns regarding safety and the environment can be reduced.

Description

Technology Field

[0001] The present invention relates to a method for inducing eel feminization by feeding eels from fry to the small eel stage with eel feed containing soy isoflavones, a method for rearing eels by feeding eels with soy isoflavones, an eel feminization agent, eel feed, etc. Background Technology

[0002] Eel is a general term for fish belonging to the genus Eel of the family Ecidae, and 19 species are known worldwide, including the Japanese eel, giant eel, and European eel. Since ancient times, it has been consumed in regions such as Europe and East Asia, and in Japan in particular, it has traditionally been a popular food ingredient.

[0003] For example, the Japanese eel (scientific name *Anguilla japonica*), which inhabits all of East Asia including Japan, is believed to spawn near the Mariana Islands in the Pacific Ocean. After becoming a larva called a leptocephalus, it metamorphoses into a nearly transparent juvenile eel measuring 5–6 cm in total length and weighing 0.2–0.3 g, and travels to coastal areas of East Asia via the currents of the Kuroshio Current. It is then presumed to settle and grow in inland waters, coastal areas, and brackish waters to become a juvenile eel (such as a *crocodile*), further mature over 5 to 10 years, and then migrate back toward spawning grounds. Other eels also share nearly identical lifestyles, although their spawning and settlement locations may differ.

[0004] Due to the size of demand and high profits, eel farming is widely practiced, and it is estimated that farmed eels account for more than 99% of total consumption. The current mainstream method of eel farming involves capturing wild eel fry that migrate to coastal areas as fry for farming, releasing them into aquaculture ponds, and raising them. Furthermore, regarding complete farming—raising fry obtained through artificial hatching into large eels and obtaining the next generation of fry—success has been reported at the laboratory level, but it has not yet reached mass production at the commercial level.

[0005] Generally, when male eels exceed 300g in weight, their growth slows down, and their bodies become hard, resulting in a decline in quality and taste. On the other hand, female eels have a higher growth limit than male eels, so even if they exceed 300g in weight, their growth does not slow down, and they grow with soft bodies, maintaining their quality and taste. However, when raised in an aquaculture environment from the juvenile stage to the adult stage, most of them become male eels, making it difficult to obtain female eels.

[0006] It is known that feminization can be induced by adding a female hormone (estradiol 17β) to the compound feed and feeding it during the period when the eel grows from a fry to a small eel. In addition, as a means of feminizing eels without using hormones, for example, Patent Document 1 describes a means of promoting feminization by rearing eels before sexual differentiation in a tank in which a hollow receiving member is arranged to cover the entire body of the eel that has entered the tank.

[0007] Herein, regarding soybean isoflavones according to the present invention, they will be described below.

[0008] Soybean isoflavones are a general term for flavonoid compounds based on the isoflavone framework, which are mainly found in large quantities in the germ of soybeans. Soybean isoflavones are classified into four types: glucoside type (glycoside; a structure covalently bonded to a sugar), aglycone type (non-glycoside; a structure in which the sugar portion of the glycoside is removed), acetylated glycosides, and malonylated glycosides. Three types of compounds are known in each category, resulting in a total of 12 known compounds as soybean isoflavones. Among them, the three glucoside type soybean isoflavones are genistein, daidzin, and glycitin, and their aglycone types (with the sugar portion removed) are genistein, daidzein, and glycitein, respectively. The composition and content of each compound vary depending on the type of raw soybeans, extraction, purification, and processing methods. In addition, as a means of separating specific compounds among soybean isoflavones, for example, Patent Document 2 discloses a means of separating high-purity genistein from an isoflavone mixture using a solvent.

[0009] Soy isoflavones have a chemical structure similar to female hormones (estrogen) and are also called phytoestrogens. Soy isoflavones in the aglycone form have estrogen-like effects and are known to be effective in preventing heart disease, menopausal disorders, osteoporosis, breast cancer, etc.

[0010] In addition, Non-patent Literature 1 describes that when European eels were fed 2 mg / kg (dry feed) of genistein for 100 days, 55% became female, whereas when fed 20 mg / kg (dry feed), which is more than that, only 15% became female. Prior art literature

[0011] Japanese Published Patent No. 2018-143182 Japanese Published Patent No. Hei 7-173148

[0012] Itai Tzchori, et al, "The influence of phytoestrogens and oestradiol-17β on growth and sex determination in the European eel (Anguilla Anguilla)", Aquaculture Research, 2004, 35, 1213-1219. The problem to be solved

[0013] As mentioned above, it is already known that eels can be feminized by adding estradiol 17β to a compound feed and feeding it. This technique is still the most reliable and highly efficient means of feminizing eels compared to other feminization techniques.

[0014] However, estradiol-17β is known to be a substance with very strong feminizing effects, even in trace amounts. In particular, aquatic organisms are more sensitive to exogenous hormones than terrestrial animals, and there have been many reported cases where reproductive functions have been disrupted by hormone-like substances in the environment. Furthermore, the potential for estradiol-17β to possess carcinogenicity and reproductive toxicity has also been pointed out. Therefore, considering the risk that the substance may be released into the environment if estradiol-17β is used in aquaculture sites, there are significant concerns regarding both environmental burden and safety regarding its actual use in aquaculture facilities.

[0015] For this reason, this technology is limited to use in research or laboratories on the premise that it is not for food, and estradiol-17β is not used to induce feminization in eel farming sites, and as of now, individuals feminized using estradiol-17β are not being released into the market.

[0016] Meanwhile, as mentioned above, even large female eels weighing around 500g have soft bodies and good quality and taste. Currently, eels weighing 200 to 250g are the mainstream in the market, but given the situation where we rely 100% on natural resources, larger sizes for distribution are required to effectively utilize eel resources. Therefore, it is estimated that there is high potential demand in the market for female eels that are easy to grow large and can maintain high quality. If reliable and highly efficient feminization induction technology can minimize concerns regarding safety and the environment, it is possible to ship farmed eels that have been feminized as food ingredients.

[0017] Accordingly, the present invention aims to provide a novel means that can reduce concerns regarding safety and the environment, and also reliably and efficiently induce eel feminization. means of solving the problem

[0018] The inventors have newly discovered that eels can be feminized by feeding them an eel feed supplemented with soybean isoflavones during the fry and small eel stages.

[0019] Accordingly, the present invention provides a method for inducing eel feminization by feeding an eel feed containing 0.05% by weight or more of soybean isoflavones in the dry matter during the stage of eel fry and / or small eel.

[0020] By feeding eel feed supplemented with soy isoflavones during a specific period of growth from juvenile eels to small eels, for example, during a period when sex is indeterminate or sexual plasticity is present, eels can be reliably and efficiently induced into feminization.

[0021] Various types of soybean foods that are routinely consumed by humans contain soybean isoflavones. For this reason, even if extremely small amounts of soybean isoflavones remain in eels that have consumed soybean isoflavones (or one or more specific compounds among them) during the growth stage, there is little concern regarding safety when humans eat those eels. Furthermore, since soybean isoflavones are a group of plant-derived compounds, even if they are released into the environment, it is highly likely that their impact on the environment will be less compared to estradiol-17β. Therefore, the present invention may make it possible to reduce concerns regarding safety and the environment compared to cases where feminization is induced using estradiol-17β.

[0022] Furthermore, by minimizing safety and environmental concerns regarding the induction of feminization in eels, there is a possibility that farmed eels with induced feminization can be shipped as food ingredients. As mentioned above, since female eels are easy to grow in size and also possess good quality and taste, it is presumed that there is high potential demand for female eels in the market. Through the present invention, it becomes possible to farm and produce female eels to meet this demand and supply them to the market.

[0023] In addition, in the present invention, "small eel" refers to a young eel that has grown larger than a juvenile eel. Hereinafter, for convenience, those weighing less than 0.5g are referred to as juvenile eels, and those weighing 0.5g or more are referred to as small eels. Effects of the invention

[0024] With the present invention, eels can be feminized with high efficiency and with minimal concerns regarding safety and the environment. Specific details for implementing the invention

[0025] <Regarding the feed for eels according to the present invention>

[0026] The present invention broadly includes eel feed containing 0.05% by weight or more of soybean isoflavones in a ratio of dry weight, eel feed containing 0.05% by weight or more of soybean isoflavone aglycones in a ratio of dry weight, and eel feed containing 0.006% by weight or more of genistein in a ratio of dry weight.

[0027] Feminization of eels can be induced by including soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds among these, e.g., genistein, etc.) in eel feed and feeding the feed for a certain period during the stage of juvenile eels and / or small eels.

[0028] In many cases, compound feed used as feed for eels is prepared by adding water, feed oil (fish oil), etc., mixing it into a paste, and then feeding it to the eels.

[0029] In the present invention, the soybean isoflavone is preferably contained in a ratio of at least 0.05% by weight, more preferably at least 0.2% by weight, and most preferably at least 1.0% by weight, in the dry feed (hereinafter the same), that is, when the weight of the feed before preparation (adding water, etc.) at the time of use is 100%. Although the upper limit of the soybean isoflavone content ratio is not particularly limited, from the perspective of feed efficiency, it is preferably 20% by weight or less, more preferably 8.0% by weight or less, and most preferably 4.0% by weight or less.

[0030] Soy isoflavones may be widely used from known sources and are not particularly limited. For example, commercially available products may be used, or isoflavones prepared by extraction, purification, and processing from raw materials such as soybeans using known methods may be used.

[0031] At another point, in terms of the proportion of the dry matter, that is, when the weight of the feed before preparation (adding water, etc.) is 100%, it is sufficient to contain soybean isoflavone aglycone, preferably 0.05% by weight or more, more preferably 0.2% by weight or more, and most preferably 1.0% by weight or more. The upper limit of the soybean isoflavone aglycone content ratio is not particularly limited, but from the perspective of feed efficiency, it is preferable to have 20% by weight or less, more preferable to have 8.0% by weight or less, and most preferable to have 4.0% by weight or less. Furthermore, "soybean isoflavone aglycone" is the non-sugar portion of soybean isoflavones (hereinafter the same), and its content weight can be obtained, for example, by converting the weight of the added soybean isoflavones into the ratio of the molecular weights of the glycosides and the aglycones, and can also be obtained by analysis using known test methods.

[0032] At another point, in terms of the proportion of the dry matter, that is, when the weight of the feed before preparation (adding water, etc.) is taken as 100%, it is sufficient to contain genistein in an amount of at least 0.006% by weight, more preferably at least 0.02% by weight, and most preferably at least 0.1% by weight. Although there is no particular limit to the upper limit of the genistein content ratio, from the perspective of feed efficiency, it is preferable to have 5.0% by weight or less, more preferable to have 2.0% by weight or less, and most preferable to have 1.0% by weight or less.

[0033] The means of incorporating genistein into eel feed are not particularly limited. For example, genistein may be incorporated into eel feed by adding soy isoflavones containing genistein to the eel feed, genistein may be added directly to the eel feed, or soy isoflavones or genistein may be incorporated in advance during the feed manufacturing stage.

[0034] Genistein can be widely used from known sources and is not particularly limited. For example, a commercially available product may be used, or soybean isoflavones containing genistein may be used as is, or those isolated or purified by extraction, purification, or processing from soybean isoflavones by known methods may be used, or those obtained by isolation, extraction, fermentation, etc. from soybeans or their processed products by known methods may be used, or those synthesized by known methods may be used. For example, if the above soybean isoflavones contain 10% by weight or more of genistein, they are relatively easy to obtain, manufacture, and prepare, and there is an advantage that they can reliably induce eel feminization with high efficiency.

[0035] In addition, the genistein according to the present invention widely includes pharmacologically acceptable salts and derivatives of genistein, provided that the feminization-inducing effect on eels is maintained.

[0036] The feed for eels according to the present invention may contain at least soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds among these, such as genistein), and is not narrowly limited by other formulations or ingredient compositions.

[0037] For example, regarding the composition of ingredients other than soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof) in eel feed, it may be the same as that of commonly used compound feed. The compound feed is a mixture of nutrients for eel growth in appropriate proportions, and for example, may contain 50% by weight or more of fish meal in the proportion of dry weight, and may also contain starch, calcium phosphate, salt, yeast, herbal extract, etc.

[0038] Regarding the fish meal in the compound feed, known types may be widely adopted and are not particularly limited; for example, powder obtained by processing sardines, mackerel, herring, horse mackerel, etc., may be used. Additionally, fish meal from other fish species may be used, or a mixture of fish meal from multiple species may be used. It can be appropriately selected by considering the type of eel, growth condition, cost, etc.

[0039] In addition, ingredients that improve the growth efficiency of eels, such as lactic acid bacteria, butyric acid bacteria, digestive enzymes, and dried vegetables, may be appropriately contained.

[0040] <Regarding the eel feminization inducer according to the present invention>

[0041] The present invention broadly includes an eel feminization inducer containing soybean isoflavone as an active ingredient, consumed at a rate of 10 mg / kg (eel body weight, hereinafter the same) or more per day; an eel feminization inducer containing soybean isoflavone aglycone as an active ingredient, consumed at a rate of 10 mg / kg or more per day; and an eel feminization inducer containing genistein as an active ingredient, consumed at a rate of 1.2 mg / kg or more per day.

[0042] The eel feminization inducer according to the present invention contains soybean isoflavone (or soybean isoflavone aglycone, or one or more specific compounds thereof, e.g., genistein) as an active ingredient. By consuming soybean isoflavone, etc. to eels during the stage of juvenile eels and / or small eels, eels can be feminized reliably and efficiently.

[0043] In the case of compound feed, the standard feeding amount is 5–8% of body weight during the fry to small eel stage (e.g., body weight of about 0.2g to 20g), and 2–3% of body weight during the growth stage (e.g., body weight of about 20g to 30g). With a feeding amount of 2% of body weight, it is desirable to consume at least 10mg / kg of soybean isoflavones per day, more desirable to consume at least 40mg / kg, and most desirable to consume at least 200mg / kg. Additionally, from the perspective of feed efficiency, with a feeding amount of 8% of body weight, it is desirable that the intake of soybean isoflavones be 16g / kg or less per day, more desirable to consume at least 6.4g / kg, and most desirable to consume at least 3.2g / kg.

[0044] At another point, the feed amount is set to 2% of body weight, and it is desirable to consume at least 10 mg / kg of soybean isoflavone aglycone per day, more desirable to consume at least 40 mg / kg, and most desirable to consume at least 200 mg / kg. In addition, from the perspective of feed efficiency, the feed amount is set to 8% of body weight, and the intake of soybean isoflavone aglycone is preferably 16 g / kg or less per day, more desirable to consume at least 6.4 g / kg, and most desirable to consume at least 3.2 g / kg.

[0045] At another point, the feed amount is set to 2% of body weight, and it is desirable to consume at least 1.2 mg / kg of genistein per day, more desirable to consume at least 4.0 mg / kg, and most desirable to consume at least 20 mg / kg. In addition, from the perspective of feed efficiency, the feed amount is set to 8% of body weight, and the genistein intake is preferably 4.0 g / kg or less per day, more desirable to consume at least 1.6 g / kg, and most desirable to consume at least 0.8 g / kg.

[0046] In the eel feminization inducer according to the present invention, excipients, lubricants, binders, disintegrants, solvents, solubilizing agents, suspending agents, buffers, isotonic agents, preservatives, antimicrobial agents, antioxidants, pH adjusters, dispersants, coloring agents, defoaming agents, etc. may be appropriately added depending on the purpose, use, formulation, etc.

[0047] Preferred examples of excipients include, for instance, lactose, sucrose, D-mannitol, starch, crystalline cellulose, hard anhydrous silica, etc.

[0048] As preferred examples of lubricants, for instance, magnesium stearate, calcium stearate, talc, colloidal silica, etc., can be used.

[0049] Preferred examples of binders include, for instance, crystalline cellulose, sucrose, D-mannitol, dextrin, hydroxypropylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone, etc.

[0050] Preferred examples of disintegrants include, for instance, starch, carboxymethylcellulose, calcium carboxymethylcellulose, sodium croscarmellose, sodium carboxymethylstarch, etc.

[0051] Preferred examples of solvents include, for instance, water for injection, alcohol, propylene glycol, macrocol, sesame oil, corn oil, etc.

[0052] Preferred examples of solubilizing aids include, for instance, polyethylene glycol, propylene glycol, D-mannitol, benzyl benzoate, ethanol, trisaminomethane, cholesterol, triethanolamine, sodium carbonate, sodium citrate, etc.

[0053] Preferred examples of suspending agents include, for instance, surfactants (stearyl triethanolamine, sodium lauryl sulfate, laurylaminopropionic acid, lecithin, benzalkonium chloride, benzethonium chloride, glycerin monostearate, etc.), hydrophilic polymers (polyvinyl alcohol, polyvinylpyrrolidone, sodium carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, etc.).

[0054] As preferred examples of buffers, buffer solutions such as phosphates, acetates, carbonates, citrates, tartrates, trihydroxymethylaminomethane, and HEPES may be used.

[0055] As preferred examples of isotonic agents, for instance, sodium chloride, glycerin, D-mannitol, etc., can be used.

[0056] Preferable examples of agents intended for preservation include, for instance, thimerosal, parahydroxybenzoic acid esters, phenoxyethanol, chlorobutanol, benzyl alcohol, phenethyl alcohol, dehydroacetic acid, sorbic acid, and various other preservatives, antibiotics, synthetic antimicrobial agents, etc.

[0057] As desirable examples of antioxidants, for instance, sulfites, ascorbic acid, etc., can be used.

[0058] Preferred examples of pH adjusters include, for instance, acids such as hydrochloric acid, carbonic acid, acetic acid, citric acid, phosphoric acid, boric acid, sulfuric acid, alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, alkali metal carbonates or bicarbonates such as sodium carbonate, alkali metal acetates such as sodium acetate, alkali metal citrates such as sodium citrate, bases such as tromethamol, monoethanolamine, diisopropanolamine, etc.

[0059] Preferred examples of dispersants include, for instance, sodium carboxymethylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone, polysorbate 80, etc.

[0060] Preferred examples of coloring agents include, for instance, caramel color, gardenia color, anthocyanin color, annatto color, paprika color, safflower color, red yeast rice color, carotene color, carotenoid color, flavonoid color, cochineal color, amaranth (Red No. 2), erythrosine (Red No. 3), Allula Red AC (Red No. 40), New Coxine (Red No. 102), Floxine (Red No. 104), Rose Bengal (Red No. 105), Acid Red (Red No. 106), Tartrazine (Yellow No. 4), Sunset Yellow FCF (Yellow No. 5), Fast Green FCF (Green No. 3), Brilliant Blue FCF (Blue No. 1), Indigo Carmine (Blue No. 2), copper chlorophyll, copper chlorophyllin sodium, etc.

[0061] Preferred examples of antifoaming agents include, for instance, dimethicone, simethicone, silicone emulsion, sorbitan sesquioleate, nonionic substances, etc.

[0062] In addition to the above, the present product may appropriately contain auxiliary ingredients, such as light-absorbing pigments that serve as preservatives and aids in efficacy (riboflavin, adenine, adenosine, etc.), chelating agents and reducing agents for stabilization (vitamin C, citric acid, etc.), carbohydrates (sorbitol, lactose, mannitol, starch, sucrose, glucose, dextran, etc.), casein digests, various vitamins, lactic acid bacteria, butyric acid bacteria, digestive enzymes, dried vegetables, etc.

[0063] <Regarding the method for inducing eel feminization according to the present invention>

[0064] The present invention includes all of the following: a method for inducing eel feminization by feeding eel feed containing 0.05% by weight or more of soybean isoflavones by a ratio of dry weight to eel during the fry and / or small fish stage; and a method for inducing eel feminization by feeding eel during the fry and / or small fish stage 10 mg / kg or more of soybean isoflavones per day. Furthermore, the present invention includes all of the following: a method for inducing eel feminization by feeding eel feed containing 0.05% by weight or more of soybean isoflavone aglycones by a ratio of dry weight to eel during the fry and / or small fish stage; and a method for inducing eel feminization by feeding eel during the fry and / or small fish stage 10 mg / kg or more of soybean isoflavone aglycones per day. In addition, the present invention includes a method for inducing eel feminization by feeding an eel feed containing 0.006% by weight or more of genistein in a ratio of dry weight during the eel fry and / or small eel stage, and a method for inducing eel feminization by feeding eels during the eel fry and / or small eel stage 1.2 mg / kg or more of genistein per day.

[0065] Eels undergo sex differentiation at a specific time while growing from juvenile eels to small eels (e.g., during the growth period from 0.2g to 30g body weight), and when they grow to a body weight of 30g or more, sex determination can be made by morphological observation of the gonads. Then, around the time of sex differentiation, for example, during the juvenile eel and / or small eel stage, by feeding eel feed containing soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds among them, e.g., genistein) in the aforementioned ratio, or from another perspective, by feeding soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds among them, e.g., genistein) within the aforementioned intake range, eels can be reliably induced to feminize with high efficiency.

[0066] Depending on the degree of growth of the eel, for example, during the stage of juvenile eel to small eel (e.g., body weight approximately 0.2g or more up to approximately 20g), soy isoflavones may be consumed at a daily dose of 25mg / kg to 16g / kg (eel body weight), more preferably at a daily dose of 100mg / kg to 6.4g / kg, and most preferably at a daily dose of 500mg / kg to 3.2g / kg; and during the stage of small eel (e.g., body weight approximately 20g or more up to approximately 30g), soy isoflavones may be consumed at a daily dose of 10mg / kg to 16g / kg (eel body weight), more preferably at a daily dose of 40mg / kg to 6.4g / kg, and most preferably at a daily dose of 200mg / kg to 3.2g / kg.

[0067] At other times, depending on the degree of growth of the eel, for example, during the stage of juvenile eel to small eel (e.g., body weight approximately 0.2g or more up to approximately 20g), soy isoflavone aglycone may be consumed at a daily dose of 25mg / kg to 16g / kg (eel body weight), more preferably at a daily dose of 100mg / kg to 12g / kg, and most preferably at a daily dose of 500mg / kg to 8g / kg; and during the stage of small eel (e.g., body weight approximately 20g or more up to approximately 30g), soy isoflavone aglycone may be consumed at a daily dose of 10mg / kg to 16g / kg (eel body weight), more preferably at a daily dose of 40mg / kg to 6.4g / kg, and most preferably at a daily dose of 200mg / kg to 3.2g / kg.

[0068] At another point in time, depending on the degree of growth of the eel, for example, during the stage of juvenile eel to small eel (e.g., body weight approximately 0.2g or more up to approximately 20g), genistein may be consumed at a rate of 3mg / kg to 4.0g / kg (eel body weight) per day, more preferably at a rate of 10mg / kg to 1.6g / kg, most preferably at a rate of 50mg / kg to 800mg / kg, and during the stage of small eel (e.g., body weight approximately 20g or more up to approximately 30g), genistein may be consumed at a rate of 1.2mg / kg to 1.5g / kg (eel body weight) per day, more preferably at a rate of 4mg to 600mg / kg, and most preferably at a rate of 20mg / kg to 300mg / kg.

[0069] The means of administering soybean isoflavones, etc. are not particularly limited. For example, this may be done by feeding eel feed containing soybean isoflavones, etc., or by administering soybean isoflavones, etc. separately from the feed, or by directly administering preparations of soybean isoflavones, etc. to individual eels.

[0070] The period for consuming soybean isoflavones, etc., may be any period including the time of sex differentiation and the periods before and after it, and is not specifically limited. For example, by continuously consuming soybean isoflavones, etc., for 2 to 6 months during the stage of juvenile eels and / or small eels, it is highly likely that eels can be reliably induced into feminization with high efficiency.

[0071] Regarding the frequency of consuming soy isoflavones, etc., it is sufficient to consume them continuously during the consumption period, and there are no specific limitations. For example, if soy isoflavones, etc. are consumed for 3 to 7 days out of a week, it is highly likely that eels can be successfully feminized with high efficiency. In addition, depending on the stage of growth of the eels, for example, during the fry stage to the small eel stage (e.g., body weight 0.2g to 20g), the daily intake may be divided into 2 to 3 additional doses, and during the small eel stage (e.g., body weight 20g to 30g), the daily intake may be given as a single dose.

[0072] <Regarding the method for raising eels according to the present invention>

[0073] The present invention includes all of the following: a method for rearing eels by feeding them an eel feed containing 0.05% by weight or more of soybean isoflavones in a ratio of dry weight during the stage of eels fry and / or small eels; and a method for rearing eels by feeding them 10 mg / kg or more of soybean isoflavones per day during the stage of eels fry and / or small eels. Furthermore, the present invention includes all of the following: a method for rearing eels by feeding them an eel feed containing 0.05% by weight or more of soybean isoflavone aglycones in a ratio of dry weight during the stage of eels fry and / or small eels; and a method for rearing eels by feeding them 10 mg / kg or more of soybean isoflavone aglycones per day during the stage of eels fry and / or small eels. In addition, the present invention includes all of the following: a method for rearing eels by feeding them an eel feed containing 0.006% by weight or more of genistein in a ratio of dry weight during the fry eel and / or small eel stage, and a method for rearing eels by feeding them 1.2 mg / kg or more of genistein per day during the fry eel and / or small eel stage.

[0074] As described above, eels can be reliably and efficiently feminized by rearing them while consuming an eel feed containing soy isoflavones (or soy isoflavon aglycones, or one or more specific compounds among them, e.g., genistein) in the aforementioned ratio, or by rearing them while consuming soy isoflavones (or soy isoflavon aglycones, or one or more specific compounds among them, e.g., genistein) in the aforementioned range of intake amounts.

[0075] The content ratio or intake amount of soybean isoflavones, etc., and the means, duration, frequency, and timing of intake are the same as above.

[0076] <Regarding the method for producing female eels according to the present invention>

[0077] The present invention includes all of the following: a method for producing female eels comprising a process of feeding eel feed containing 0.05% by weight or more of soybean isoflavones by dry weight ratio during the stage of eel fry and / or small eels; and a method for producing female eels comprising a process of feeding eels during the stage of eel fry and / or small eels at 10 mg / kg or more of soybean isoflavones per day. Furthermore, the present invention includes all of the following: a method for producing female eels comprising a process of feeding eel feed containing 0.05% by weight or more of soybean isoflavone aglycones by dry weight ratio during the stage of eel fry and / or small eels; and a method for producing female eels comprising a process of feeding eels during the stage of eel fry and / or small eels at 10 mg / kg or more of soybean isoflavone aglycones per day. In addition, the present invention includes a method for producing female eels comprising a process of feeding eel feed containing 0.006% by weight or more of genistein in a ratio of dry weight during the fry eel and / or small eel stage, and a method for producing female eels comprising a process of feeding eels during the fry eel and / or small eel stage 1.2 mg / kg or more of genistein per day.

[0078] The content ratio or intake amount of soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds among them, e.g., genistein), and the means, duration, frequency, and timing of intake are the same as above.

[0079] Furthermore, the present invention broadly includes female eels produced by the aforementioned method for inducing eel feminization, eel rearing method, or female eel production method. Identification of whether a female eel is produced by the method according to the present invention can be determined, for example, by the frequency of female appearance and whether it possesses the characteristics of a farmed eel.

[0080] Furthermore, the type of eel subject to the present invention may be any one belonging to the genus Anguilla of the family Anguillaceae, and is not particularly limited. For example, the Japanese eel (scientific name "Anguilla japonica"), the giant eel (scientific name "Anguilla marmorata"), the European eel (scientific name "Anguilla anguilla"), the American eel (scientific name "Anguilla rostrata"), and the bicolor eel (scientific name "Anguilla bicolor bicolor") are also subject to the invention. In the present invention, it is most preferable that the eel be the Japanese eel.

[0081] [Example 1]

[0082] In Example 1, we examined whether eels could be feminized using soy isoflavones.

[0083] Sex-undetermined eel fry (average weight 0.4g) were placed in 150L FRP tanks with 70 eels in each group, fed a compound feed containing soybean isoflavones in each ratio, and reared with the water temperature set to 28℃.

[0084] The feeding frequency of the compound feed supplemented with soybean isoflavones was set to 5 times per week. The amount fed per feeding was 7–8% of body weight during the first 2 months, and then about 2.5% of body weight thereafter.

[0085] After about 6 months from the start of rearing, individuals that had grown into small fish weighing about 30g or more were appropriately sampled, and sex determination was performed.

[0086] Sex determination was based on the morphological observation of the gonads, identifying those with ovaries as female and those with testes as male.

[0087] The results are shown in Tables 1 and 2. In each table, “number of individuals” indicates the number of small fish sampled, “soybean isoflavone addition ratio” indicates the ratio of the amount of soybean isoflavone added (weight%) when the weight of the compound feed before preparation for use and before addition of soybean isoflavone is 100%, “aglycone content ratio” indicates the ratio of the weight of soybean isoflavone aglycone (weight%) when the weight of the compound feed before preparation for use and before addition of soybean isoflavone is 100%, and “genistein content ratio” indicates the ratio of the weight of genistein (weight%) when the weight of the compound feed before preparation for use and before addition of soybean isoflavone is 100%, respectively, and “female ratio” indicates the ratio of females among the number of sampled individuals. Furthermore, "weight of soybean isoflavone aglycone content" represents the weight of the non-sugar portion of the added soybean isoflavones, and the analytical value obtained based on known test methods was used. In addition, "control" refers to the result obtained when the animals were raised by feeding them a standard compound feed that does not contain added soybean isoflavones.

[0088] [Table 1]

[0089]

[0090] [Table 2]

[0091]

[0092] As shown in Table 1, feminization of eels could be induced by adding 1% by weight or more of soy isoflavones to eel feed during the juvenile to young eel stages. In addition, as shown in Table 2, when eels were reared with eel feed containing 0 to 0.040% by weight of aglycone relative to the feed weight, all individuals differentiated into males. However, when the aglycone content was 0.100% by weight or more, 46% of the individuals were induced to become feminized, when it was 0.336% by weight, 95% of the individuals were induced to become feminized, and when it was 1.076% by weight or more, all individuals were induced to become feminized. From another perspective, focusing on genistein contained in the feed due to the addition of soybean isoflavones, when the eels were reared with an eel feed containing 0 to 0.004% by weight of genistein during the juvenile to young eel stage, all individuals were differentiated into males, whereas when the genistein content was 0.01% by weight, 46% of the individuals were induced to become female, and when the genistein content was 0.031% by weight, 95% of the individuals were induced to become female, and when the genistein content was 0.155% by weight or higher, all individuals were induced to become female.

[0093] In this experiment, the amount of food consumed per meal is calculated from the fact that it is 7-8% of body weight for the first 2 months and about 2.5% of body weight thereafter. When the soy isoflavone addition ratio is 1% by weight, the amount of soy isoflavone consumed per meal during the first 2 months is about 700-800 mg / kg body weight, and the amount of soy isoflavone consumed per meal thereafter is about 250 mg / kg body weight. Similarly, when the aglycone content ratio to feed weight is 0.100 wt%, the aglycone intake per meal during the first two months is approximately 70.0–80.0 mg / kg body weight, and thereafter, the aglycone intake per meal is approximately 25.0 mg / kg body weight; when the aglycone content ratio to feed weight is 0.336 wt%, the aglycone intake per meal during the first two months is approximately 235.2–268.8 mg / kg body weight, and thereafter, the aglycone intake per meal is approximately 84.0 mg / kg body weight; and when the aglycone content ratio to feed weight is 1.076 wt%, the aglycone intake per meal during the first two months is approximately 753.2–860.8 mg / kg body weight, and thereafter, the aglycone intake per meal is approximately It is 269.0 mg / kg body weight. In addition, when the genistein content ratio is 0.01% by weight, the genistein intake per dose during the first two months is about 7–8 mg / kg body weight, and thereafter the genistein intake per dose is about 2.5 mg / kg body weight; when the genistein content ratio is 0.031% by weight, the genistein intake per dose during the first two months is about 21.70–24.8 mg / kg body weight, and thereafter the genistein intake per dose is about 7.75 mg / kg body weight; and when the genistein content ratio is 0.155% by weight, the genistein intake per dose during the first two months is about 108.5–1,240 mg / kg body weight, and thereafter the genistein intake per dose is about 38.75 mg / kg body weight.

Claims

Claim 1 A method for inducing eel feminization by feeding eel feed containing at least 0.1% by weight of soybean isoflavone aglycone in the dry weight ratio during the stage of eel fry and / or small eels. Claim 2 A method for inducing eel feminization according to claim 1, wherein the eel feed contains 0.01% by weight or more of genistein in a ratio of dry matter. Claim 3 A method for inducing eel feminization according to claim 1, wherein the eel is a Japanese eel. Claim 4 A method for rearing eels during the fry and / or small eel stage, wherein the eels are fed an eel feed containing 0.1% by weight or more of soybean isoflavone aglycone in proportion to the dry weight. Claim 5 A method for producing female eels, comprising the process of feeding eel feed containing at least 0.1% by weight of soybean isoflavone aglycone in a proportion of dry weight during the stage of fry eels and / or small eels. Claim 6 Eel feed containing 0.1% by weight or more of soybean isoflavone aglycone in proportion to the dry weight. Claim 7 In claim 6, eel feed containing 0.01% by weight or more of genistein as a percentage of the dry weight. Claim 8 delete Claim 9 delete Claim 10 delete

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