Method for inducing eel feminization, method for raising eels, eel feminizing agent, and eel feed

Abstract

[Objective] To provide novel methods, etc., that can reduce safety and environmental concerns while reliably and efficiently inducing eel feminization. [Method] The present invention provides methods, etc., for inducing eel feminization, which involve ingesting an eel feed containing 0.05% or more by weight of soy isoflavones, based on dry matter, during the glass eel and / or smolt stage. By ingesting the eel feed supplemented with soy isoflavones during a predetermined period of growth from glass eels to smolt eels, such as during a period when their sex is undetermined or when they exhibit sexual plasticity, feminization can be reliably and efficiently induced in the eels, further reducing safety and environmental concerns.

Description

Technical Field

[0001] The present invention relates to a method for inducing eel feminization by causing glass eels to juvenile eels to ingest eel feed containing soy isoflavones, a method for raising eels by causing eels to ingest soy isoflavones, an eel feminizing agent, an eel feed, and the like. Background Art

[0002] Eel is a general term for fish belonging to the genus Anguilla in the family Anguilla. There are 19 known species worldwide, including the Japanese eel, the flower eel, and the European eel. Eel has been consumed throughout Europe and East Asia since ancient times, and is particularly popular in Japan, where it is a traditional food.

[0003] For example, the Japanese eel (Anguilla japonica), which inhabits various parts of East Asia, including Japan, is believed to spawn near the Mariana Islands in the Pacific Ocean. After spawning as a juvenile eel (Leptocephalus), it metamorphoses into nearly transparent glass eels, measuring 5 to 6 cm in length and weighing 0.2 to 0.3 grams. They then travel on the Kuroshio Current to coastal areas of East Asia. It is then presumed to settle in inland waters, coastal areas, and brackish waters, where they mature into young eels (such as black fry). After five to ten years, they mature and return to their spawning grounds. Other eels follow a similar lifestyle, although spawning and settlement locations may vary.

[0004] Due to high demand and high profits, eels are widely farmed, accounting for over 99% of all eels consumed. Currently, the mainstream eel farming method involves capturing naturally occurring glass eels that migrate to coastal areas as seedlings, releasing them into aquaculture ponds, and raising them to mature. While there are reports of successful laboratory trials of artificially hatched fry to produce parent eels and the next generation of fry, commercial production has yet to be achieved.

[0005] Typically, male eels grow slower after they exceed 300g, becoming tougher and less delicious. Female eels, on the other hand, have a longer growth limit than males, and even when they exceed 300g, their growth continues without slowing down, maintaining a soft and tender texture and maintaining the same quality and flavor. However, if they are raised in captivity during the transition from glass eels to juvenile eels, most of them become males, making it difficult to obtain female eels.

[0006] It is known that feminization can be induced by adding female hormones (estradiol 17β) to a formula feed during the growth period of glass eels into young eels. Furthermore, as a method for feminizing eels without the use of hormones, Patent Document 1, for example, describes a method for promoting feminization by raising eels before sexual differentiation in a tank equipped with a hollow container that covers the entire eel's body.

[0007] Here, soybean isoflavones will be described below as a matter related to the present invention.

[0008] Soy isoflavones are a general term for flavonoid compounds with isoflavone as the basic skeleton, and are mainly found in large quantities in soybean germs and other materials. Soy isoflavones are divided into four types: glycoside type (glycoside; structure covalently bound to sugar), aglycone type (non-glycoside; structure with the sugar portion of the glycoside detached), acetylated glycoside, and malonylated glycoside. Three compounds are known in each category, for a total of 12 known soy isoflavone compounds. The three glycoside-type soy isoflavones are genistin, daidzein, and glycitein, while their aglycone types (with the sugar portion detached) are genistein, daidzein, and glycitein, respectively. The composition and content of each compound vary depending on the type of raw soybean, etc., and the extraction, purification, and processing methods. Furthermore, as a method for isolating specific compounds from soy isoflavones, Patent Document 2, for example, discloses a method for isolating high-purity genistein from an isoflavone mixture using a solvent.

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

[0010] Furthermore, Non-Patent Document 1 describes that when European eels were fed 2 mg / kg (dry feed) of genistein for 100 days, 55% of them became females. In contrast, when they were fed a higher dose of 20 mg / kg (dry feed), only 15% of them became females.

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2018-143182

[0012] [Patent Document 2] Japanese Patent Application Laid-Open No. 7-173148

[0013] [Non-patent document 1] Itai Tzchori, et al, "The influence of phytoestrogens andoestradiol-17β on growth and sex determination in the European eel (Anguilla Anguilla)", Aquaculture Research, 2004, 35, 1213-1219. Summary of the Invention

[0014] As mentioned above, it is known that eels can be feminized by adding estradiol 17β to their formulated feed. Compared to other feminization techniques, this technique remains the most reliable and efficient method for inducing eel feminization.

[0015] However, estradiol-17β is known to have a very strong feminizing effect, even in trace amounts. Aquatic organisms are particularly sensitive to exogenous hormones compared to terrestrial animals, and there have been numerous reports of reproductive disorders caused by hormones in environmental water. Furthermore, there are concerns about the potential carcinogenicity and reproductive toxicity of estradiol-17β. Therefore, given the potential for release of estradiol-17β into the water, its use in aquaculture raises significant concerns regarding both environmental impact and safety.

[0016] Therefore, this technology is only used for research purposes without the need for food or in laboratories. Estradiol 17β has not been used to induce feminization in eel farms. Currently, individuals induced to be feminized using estradiol 17β are not sold on the market.

[0017] On the other hand, as mentioned above, even large female eels weighing approximately 500g have tender flesh, good quality, and excellent flavor. Currently, eels weighing 200-250g are the mainstream on the market. Given 100% reliance on natural resources, the efficient use of eel resources requires larger sizes for distribution. Therefore, there is expected to be a significant potential demand for female eels that can be easily scaled up while maintaining high quality. If reliable and efficient feminization techniques can be developed to mitigate safety and environmental concerns, it would be possible to market feminized farmed eels as food.

[0018] Therefore, an object of the present invention is to provide a novel method for inducing the feminization of eels reliably and efficiently while reducing concerns about safety and environment.

[0019] Solutions to the Problem

[0020] The present inventors have newly discovered that feminization of glass eels and eels in their juvenile stage can be induced by feeding eel feed supplemented with soy isoflavones.

[0021] Therefore, the present invention provides a method for inducing feminization of eels, etc., which comprises allowing eels to ingest eel feed containing 0.05% by weight or more of soy isoflavones in terms of dry matter when they are glass eels and / or young eels.

[0022] By allowing glass eels to consume eel feed supplemented with soy isoflavones during a predetermined period of their growth from glass eels to baby eels, for example, during a period when their sex is undetermined or sexually plastic, feminization of the eels can be induced reliably and efficiently.

[0023] Many soy foods consumed daily as human food contain soy isoflavones. Therefore, even if trace amounts of soy isoflavones remain in eels that have been exposed to soy isoflavones (or one or more specific compounds thereof) during their growth phase, there are minimal safety concerns for humans when consuming the eels. Furthermore, soy isoflavones are a group of plant-derived compounds, so even if released into the environment, they are likely to have less impact than, for example, estradiol 17β. Therefore, compared to using estradiol 17β and other substances for feminization induction, the present invention can further reduce safety and environmental concerns.

[0024] Furthermore, by alleviating safety and environmental concerns regarding the induction of feminization in eels, it is possible to market feminized farmed eels as food. As mentioned above, female eels easily grow to large sizes and have excellent quality and flavor, so it is speculated that there is a significant potential market demand for them. The present invention makes it possible to respond to this demand by farming and producing female eels for market supply.

[0025] In addition, in the present invention, the so-called "small eel" refers to an eel fry that grows larger than a glass eel. For convenience, eels weighing less than 0.5g are hereinafter referred to as glass eels, and eels weighing more than 0.5g are referred to as small eels.

[0026] Effects of the Invention

[0027] According to the present invention, concerns about safety and environment can be reduced, and eels can be induced to feminize reliably and efficiently. DETAILED DESCRIPTION

[0028] <About the eel feed of the present invention>

[0029] The present invention broadly encompasses: eel feed containing 0.05% by weight or more of soy isoflavones based on a ratio in dry matter, eel feed containing 0.05% by weight or more of soy isoflavone aglycones based on a ratio in dry matter, and eel feed containing 0.006% by weight or more of genistein based on a ratio in dry matter.

[0030] By making eel feed contain soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein), and feeding this feed to glass eels and / or young eels for a certain period of time, the feminization of eels can be induced.

[0031] Formulated feed used as eel feed is often prepared by adding water, feed oil (fish oil), etc., kneading it into a paste, and then feeding it to eels.

[0032] In the present invention, based on the dry matter ratio (hereinafter referred to as the feed weight before preparation (addition of water, etc.) as 100%, the feed preferably contains 0.05% by weight or more of soy isoflavones, more preferably 0.2% by weight or more, and most preferably 1.0% by weight or more. There is no particular upper limit on the soy isoflavone content; however, 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.

[0033] Soy isoflavones can be widely used and are not particularly limited. For example, ready-made products can be used, or soy isoflavones prepared by extraction, purification, and treatment from raw materials such as soybeans by known methods can be used.

[0034] From another perspective, when the ratio in dry matter, that is, the weight of the feed before preparation (adding water, etc.) is set to 100%, it is preferred that it contains more than 0.05% by weight of soy isoflavone aglycones, more preferably more than 0.2% by weight, and most preferably more than 1.0% by weight. There is no particular limitation on the upper limit of the soy isoflavone aglycone content ratio. From the perspective of feed efficiency, etc., it is preferably less than 20% by weight, more preferably less than 8.0% by weight, and most preferably less than 4.0% by weight. In addition, "soy isoflavone aglycone" is the non-sugar part in soy isoflavones (the same below), and its weight content can be obtained by, for example, converting the weight of the soy isoflavones added by the ratio of the molecular weight of the glycoside to the aglycone, and can also be obtained by analyzing using a known test method.

[0035] From other perspectives, in terms of the ratio in dry matter, that is, when the feed weight before the preparation (addition of water, etc.) is set to 100%, it is preferred to contain more than 0.006 weight % of genistein, more preferably more than 0.02 weight %, and most preferably more than 0.1 weight %. About the upper limit of genistein containing ratio, there is no particular limitation. From the viewpoint of feed efficiency, it is preferably less than 5.0 weight %, more preferably less than 2.0 weight %, and most preferably less than 1.0 weight %.

[0036] There are no particular limitations on the method for adding genistein to eel feed. For example, genistein can be added to eel feed by adding soy isoflavones containing genistein to eel feed. Genistein can also be added directly to eel feed. Soy isoflavones or genistein can also be pre-added to eel feed during the production stage.

[0037] Genistein can widely adopt known ones, and is not particularly limited.For example, ready-made products can be used, the soybean isoflavones containing genistein can also be directly used, the genistein of extraction, purification, processing and separation or high purification can also be used from soybean isoflavones etc. by known methods, the genistein obtained by separation, extraction, fermentation etc. from beans or its processed products can also be used, and the genistein synthesized by known methods can also be used.For example, when the soybean isoflavones contain the genistein more than 10 weight %, there is the following advantage: relatively easy to obtain, manufacture, prepare, and can reliably and efficiently induce the feminization of eels.

[0038] Furthermore, the genistein of the present invention also broadly encompasses pharmacologically acceptable salts thereof and genistein derivatives as long as the genistein maintains the feminization-inducing effect on eels.

[0039] The eel feed of the present invention only needs to contain soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein), and is not narrowly limited to other formulas, component compositions, etc.

[0040] For example, the formula and composition of eel feed, other than the soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof), can be the same as those of commonly used formulated feeds. Formulated feeds are feeds that contain nutrients necessary for eel growth in appropriate proportions, such as fish meal (50% by weight or more on a dry matter basis), and may further contain starch, calcium phosphate, salt, yeast, herbal extracts, and the like.

[0041] The fish meal in the formulated feed can be widely used and is not particularly limited. For example, it can be powder obtained by processing sardines, mackerel, herring, horse mackerel, etc. Furthermore, it can be fish meal from other fish species, or a mixed powder of fish meal from multiple fish species. The appropriate choice can be made based on the type of eel, growth status, cost, and other factors.

[0042] Furthermore, for example, components that improve the growth efficiency of eels, such as lactic acid bacteria, butyric acid bacteria, digestive enzymes, and dried vegetables, may be appropriately contained.

[0043] <About the eel feminization inducer of the present invention>

[0044] The present invention broadly includes: eel feminization inducers containing soy isoflavones as active ingredients at a daily intake of 10 mg / kg (eel body weight, the same below) or more, eel feminization inducers containing soy isoflavone aglycones as active ingredients at a daily intake of 10 mg / kg or more, and eel feminization inducers containing genistein as active ingredients at a daily intake of 1.2 mg / kg or more, etc.

[0045] The eel feminization inducer of the present invention contains soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) as an active ingredient. By ingesting soy isoflavones and the like during the glass eel and / or young eel stage, the eel can be reliably and efficiently feminized.

[0046] In the case of a formulated feed, the usual feeding amount standard is 5-8% of body weight during the glass eel to small eel period (for example, weighing 0.2g to 20g), and 2-3% of body weight during the small eel period (for example, weighing 20g to 30g) depending on growth conditions. The feeding amount is set to 2% of body weight, preferably 10mg / kg or more of soy isoflavones are taken per day, more preferably 40mg / kg or more, and most preferably 200mg / kg or more. Moreover, from the perspective of feed efficiency, the feeding amount is set to 8% of body weight, and the soy isoflavone intake is preferably 16g / kg or less per day, more preferably 6.4g / kg or less per day, and most preferably 3.2g / kg or less per day.

[0047] From another perspective, when the feeding amount is set to 2% of body weight, it is preferred to ingest 10 mg / kg or more of soy isoflavone aglycones per day, more preferably 40 mg / kg or more, and most preferably 200 mg / kg or more. Furthermore, from the perspective of feed efficiency, when the feeding amount is set to 8% of body weight, the intake of soy isoflavone aglycones is preferably 16 g / kg or less per day, more preferably 6.4 g / kg or less per day, and most preferably 3.2 g / kg or less per day.

[0048] From another perspective, when the feeding amount is set to 2% of body weight, it is preferred to take 1.2 mg / kg or more of genistein per day, more preferably 4.0 mg / kg or more per day, and most preferably 20 mg / kg or more per day. Moreover, from the perspective of feed efficiency, when the feeding amount is set to 8% of body weight, the intake of genistein is preferably 4.0 g / kg or less per day, more preferably 1.6 g / kg or less per day, and most preferably 0.8 g / kg or less per day.

[0049] The eel feminization inducer of the present invention may contain excipients, lubricants, binders, disintegrants, solvents, solubilizers, suspending agents, buffers, isotonic agents, preservatives, antibacterial agents, antioxidants, pH adjusters, dispersants, colorants, defoaming agents, etc., depending on the purpose, application, dosage form, etc.

[0050] Preferred examples of the excipient include lactose, granulated sugar, D-mannitol, starch, crystalline cellulose, and light anhydrous silicic acid.

[0051] Preferred examples of lubricants include magnesium stearate, calcium stearate, talc, and colloidal silicon dioxide.

[0052] Preferred examples of the binder include crystalline cellulose, granulated sugar, D-mannitol, dextrin, hydroxypropyl cellulose, hydroxypropyl methylcellulose, and polyvinyl pyrrolidone.

[0053] Preferred examples of disintegrants include starch, carboxymethyl cellulose, carboxymethyl cellulose calcium, croscarmellose sodium, and sodium carboxymethyl starch.

[0054] Preferable examples of the solvent include water for injection, alcohol, propylene glycol, polyethylene glycol (MACROGOL), sesame oil, corn oil and the like.

[0055] Preferred examples of the solubilizing agent include polyethylene glycol, propylene glycol, D-mannitol, benzyl benzoate, ethanol, trisaminomethane, cholesterol, triethanolamine, sodium carbonate, sodium citrate, and the like.

[0056] Preferred examples of suspending agents include surfactants (stearyl triethanolamine, sodium lauryl sulfate, lauryl aminopropionic acid, lecithin, benzalkonium chloride, benzethonium chloride, glyceryl monostearate, etc.), hydrophilic polymers (polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), and the like.

[0057] Preferred examples of the buffer include buffers such as phosphate, acetate, carbonate, citrate, tartrate, Tris, and HEPES.

[0058] Preferred examples of the isotonic agent include sodium chloride, glycerol, and D-mannitol.

[0059] Preferred examples of drugs for the purpose of preservation include thimerosal, parabens, phenoxyethanol, chlorobutanol, benzyl alcohol, phenylethyl alcohol, dehydroacetic acid, sorbic acid, other various preservatives, antibiotics, synthetic antibacterial agents, and the like.

[0060] Preferred examples of antioxidants include sulfites and ascorbic acid.

[0061] Preferred examples of pH adjusters include acids such as hydrochloric acid, carbonic acid, acetic acid, citric acid, phosphoric acid, boric acid, and sulfuric acid; alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide; alkali metal carbonates or hydrogencarbonates such as sodium carbonate; alkali metal acetates such as sodium acetate; alkali metal citrates such as sodium citrate; bases such as trometamol; monoethanolamine; and diisopropanolamine.

[0062] Preferred examples of the dispersant include sodium carboxymethylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone, and polysorbate 80.

[0063] Preferred examples of colorants include caramel color, gardenia pigment, anthocyanin pigment, annatto pigment, paprika pigment, safflower pigment, monascus pigment, carotene pigment, carotenoid pigment, flavonoid pigment, cochineal pigment, amaranth (Red No. 2), erythrosine (Red No. 3), allura red AC (Red No. 40), carmine (Red No. 102), fluorescent pink (Red No. 104), rose Bengal (Red No. 105), acid red (Red No. 106), tartrate (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 chlorophyllin, and sodium copper chlorophyllin.

[0064] Preferred examples of the defoaming agent include dimethicone, simethicone, silicone emulsion, sorbitan sesquioleate, and nonionic substances.

[0065] In addition to the above, this agent may also contain auxiliary ingredients as appropriate, such as light-absorbing pigments (riboflavin, adenine, adenosine, etc.) as preservation and efficacy aids, 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.

[0066] <About the method for inducing eel feminization of the present invention>

[0067] The present invention encompasses all methods for inducing feminization in eels, including methods for ingesting an eel feed containing 0.05% or more of soy isoflavones based on dry matter during the glass eel and / or smolt eel stage, and methods for ingesting 10 mg / kg or more of soy isoflavones daily during the glass eel and / or smolt eel stage. Furthermore, the present invention encompasses all methods for inducing feminization in eels, including methods for ingesting an eel feed containing 0.05% or more of soy isoflavone aglycones based on dry matter during the glass eel and / or smolt eel stage, and methods for ingesting 10 mg / kg or more of soy isoflavone aglycones daily during the glass eel and / or smolt eel stage. In addition, the present invention includes all of the following methods for inducing feminization in eels: a method for causing eels to ingest eel feed containing 0.006 weight percent or more of genistein in terms of dry matter when they are glass eels and / or young eels; and a method for causing eels in the glass eels and / or young eels to ingest 1.2 mg / kg or more of genistein per day, etc.

[0068] Eels undergo male-female differentiation at a specific time during their growth from glass eels to smolts (e.g., during the growth period with a body weight of 0.2 g to 30 g). When they grow to a body weight of 30 g or more, sex differentiation can be performed by observing the morphology of the gonads. Furthermore, before and after the male-female differentiation period, for example, during the glass eel and / or smolt eel period, eels can be feminized reliably and efficiently by ingesting a feed containing soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) at the above ratio, or from another perspective, by ingesting soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) within the above intake range.

[0069] Depending on the growth level of the eel, for example, in the period from glass eel to small eel (for example, weighing slightly more than 0.2g and slightly less than 20g), it can be made to take in 25mg / kg to 16g / kg (eel body weight) of soy isoflavones per day, more preferably 100mg / kg to 6.4g / kg per day, and most preferably 500mg / kg to 3.2g / kg per day; in the period of small eel (for example, weighing slightly more than 20g to slightly 30g), it can be made to take in 10mg / kg to 16g / kg (eel body weight) of soy isoflavones per day, more preferably 40mg / kg to 6.4g / kg per day, and most preferably 200mg / kg to 3.2g / kg per day.

[0070] From another perspective, depending on the growth rate of the eel, for example, in the period from glass eels to small eels (for example, weighing slightly more than 0.2g and slightly less than 20g), they can be made to ingest 25mg / kg to 16g / kg (eel body weight) of soy isoflavone aglycones per day, more preferably 100mg / kg to 12g / kg per day, and most preferably 500mg / kg to 8g / kg per day; in the period from small eels (for example, weighing slightly more than 20g to slightly 30g), they can be made to ingest 10mg / kg to 16g / kg (eel body weight) of soy isoflavone aglycones per day, more preferably 40mg / kg to 6.4g / kg per day, and most preferably 200mg / kg to 3.2g / kg per day.

[0071] From another perspective, depending on the growth rate of the eel, for example, in the period from glass eel to small eel (for example, weighing slightly more than 0.2g and slightly less than 20g), it can be made to take in 3mg / kg to 4.0g / kg (eel body weight) of genistein per day, more preferably 10mg / kg to 1.6g / kg per day, and most preferably 50mg / kg to 800mg / kg per day; in the period of small eel (for example, weighing slightly more than 20g to slightly 30g), it can be made to take in 1.2mg / kg to 1.5g / kg (eel body weight) of genistein per day, more preferably 4mg to 600mg / kg per day, and most preferably 20mg / kg to 300mg / kg per day.

[0072] The method for ingesting soy isoflavones and the like into eels is not particularly limited. For example, eels can be fed with feed containing soy isoflavones and the like, eels can ingest soy isoflavones and the like separately from the feed, or preparations containing soy isoflavones and the like can be directly administered to individual eels.

[0073] The period for ingesting soy isoflavones and the like in eels is not particularly limited, as long as it is during the period of male-female differentiation and the period before and after. For example, by continuously ingesting soy isoflavones and the like in glass eels and / or young eels for 2 to 6 months during their sexual differentiation period, there is a high probability that feminization of eels can be reliably and efficiently induced.

[0074] The frequency of ingesting soy isoflavones and the like by the eels is not particularly limited, as long as the eels are ingested continuously without interruption during the ingestion period. For example, by ingesting soy isoflavones and the like by the eels 3 to 7 days a week, there is a high probability that the feminization of the eels can be reliably and efficiently induced. Furthermore, depending on the growth of the eels, for example, in the period of glass eels to small eels (e.g., weighing 0.2g to 20g), the daily intake can be further divided into 2 to 3 doses. In the period of small eels (e.g., weighing 20g to 30g), the daily intake can be administered in a single dose.

[0075] <About the eel breeding method of the present invention>

[0076] The present invention encompasses all methods for raising eels, including methods for feeding eels a feed containing 0.05% by weight or more of soy isoflavones based on dry matter during the glass eel and / or smolt eel stage; and methods for causing eels to ingest 10 mg / kg or more of soy isoflavones daily during the glass eel and / or smolt eel stage. Furthermore, the present invention encompasses all methods for raising eels, including methods for feeding eels a feed containing 0.05% by weight or more of soy isoflavone aglycones based on dry matter during the glass eel and / or smolt eel stage; and methods for causing eels to ingest 10 mg / kg or more of soy isoflavone aglycones daily during the glass eel and / or smolt eel stage. In addition, the present invention includes all of the following eel breeding methods: a method of causing eels to ingest eel feed containing 0.006 weight percent or more of genistein in terms of dry matter when they are glass eels and / or young eels; and a method of causing eels in the glass eels and / or young eels to ingest 1.2 mg / kg or more of genistein per day, etc.

[0077] As described above, before and after the period of male-female differentiation, for example, during the glass eel and / or small eel period, the eels are fed with eel feed containing soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) at the above ratio. From another perspective, eels are fed with soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) within the above intake range, thereby reliably and efficiently inducing feminization of eels.

[0078] The content ratio or intake amount of soy isoflavones, etc., and the method, period, frequency, time, etc. of eel intake are the same as those described above.

[0079] <Regarding the method for producing female eels of the present invention>

[0080] The present invention encompasses all methods for producing female eels, including the steps of causing the glass eel and / or smolt eel to ingest an eel feed containing 0.05% by weight or more of soy isoflavones based on dry matter, and the steps of causing the glass eel and / or smolt eel to ingest 10 mg / kg or more of soy isoflavones daily. Furthermore, the present invention encompasses all methods for producing female eels, including the steps of causing the glass eel and / or smolt eel to ingest an eel feed containing 0.05% by weight or more of soy isoflavone aglycones based on dry matter, and the steps of causing the glass eel and / or smolt eel to ingest 10 mg / kg or more of soy isoflavone aglycones daily. In addition, the present invention includes all of the following methods for producing female eels: a method comprising the step of causing the eels to ingest eel feed containing 0.006 weight percent or more of genistein in terms of dry matter when they are glass eels and / or young eels; and a method comprising the step of causing eels in the glass eels and / or young eels to ingest 1.2 mg / kg or more of genistein per day, etc.

[0081] The content ratio or intake amount of soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) is such that the method, period, frequency, and timing of eel ingestion are the same as those described above.

[0082] Furthermore, the present invention broadly encompasses female eels produced or produced using the aforementioned methods for inducing eel feminization, methods for raising eels, or methods for producing female eels. Identifying whether an eel is female produced or produced using the methods of the present invention can be done, for example, by determining the frequency of female eels and whether they possess characteristics characteristic of farmed eels.

[0083] The present invention also includes eels of any species belonging to the genus Anguilla, family Anguillidae, and is not particularly limited. For example, the Japanese eel (scientific name: Anguilla japonica), the flower 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 included. In the present invention, the most preferred eel is the Japanese eel.

[0084] [Example 1]

[0085] In Example 1, it was investigated whether soy isoflavones could be used to induce feminization in eels.

[0086] Glass eels of undetermined sex (average weight 0.4 g) were placed in groups of 70 in a 150 L FRP tank and fed with a formulated feed supplemented with soy isoflavones at various ratios. The water temperature was set at 28°C for breeding.

[0087] The soy isoflavone-supplemented diet was fed five times a week, with the amount of feed per week being 7-8% of body weight for the first two months and approximately 2.5% thereafter.

[0088] After about 6 months from the start of breeding, small eels that have grown to a weight of about 30 g or more are sampled and sexed.

[0089] Sex determination is based on the morphological observation of the gonads; individuals with ovaries are identified as female, and individuals with testes are identified as male.

[0090] The results are shown in Tables 1 and 2. In each table, "number of eels" represents the number of individuals of the sampled eels, "soy isoflavone addition ratio" represents the ratio (weight %) of the amount of soy isoflavone added when the weight of the formula feed before soy isoflavones is set to 100%, "aglycone content ratio" represents the ratio (weight %) of the weight of the formula feed before soy isoflavones is set to 100%, "genistein content ratio" represents the ratio (weight %) of the weight of the formula feed before soy isoflavones is set to 100%, and "female ratio" represents the ratio of females in the number of individuals sampled. In addition, "soy isoflavone aglycone content weight" represents the weight of the non-sugar part in the added soy isoflavones, using the analytical value obtained based on a known test method. In addition, "control" is the result of feeding the normal formula feed without soy isoflavones instead of the above situation.

[0091] [Table 1]

[0092]

[0093]

[0094] [Table 2]

[0095]

[0096] As shown in Table 1, feminization of eels can be induced by adding 1% by weight or more of soy isoflavones to eel feed during the glass eel to small eel stages. Furthermore, as shown in Table 2, when eels were fed eel feed containing 0 to 0.040% by weight of aglycones relative to the feed weight, all individuals differentiated into males. In contrast, when the aglycone content was 0.100% by weight or higher, 46% of the individuals were induced into females; when the content was 0.336% by weight, 95% of the individuals were induced into females; and when the content was 1.076% by weight or higher, all individuals were induced into females. From another point of view, focusing on genistein contained in feed by adding soy isoflavones, when glass eels to small eels were fed with eel feed containing genistein at a ratio of 0 to 0.004 weight%, all individuals differentiated into males, when the genistein content was 0.01 weight%, 46% of the individuals were induced to become females, when it was 0.031 weight%, 95% of the individuals were induced to become females, and when the genistein content was 0.155 weight% or more, all individuals were induced to become females.

[0097] According to the feeding amount in this experiment, it was 7-8% of body weight in the first two months and about 2.5% of body weight thereafter. When the soy isoflavone addition ratio was 1 weight%, the soy isoflavone intake in the first two months was about 700-800 mg / kg body weight, and the soy isoflavone intake thereafter was about 250 mg / kg body weight. Similarly, when the aglycone content ratio relative to the weight of the feed is 0.100 weight %, the aglycone intake each time in the first two months is approximately 70.0 to 80.0 mg / kg, and the aglycone intake each time thereafter is approximately 25.0 mg / kg body weight; when the aglycone content ratio relative to the weight of the feed is 0.336 weight %, the aglycone intake each time in the first two months is approximately 235.2 to 268.8 mg / kg body weight, and the aglycone intake each time thereafter is approximately 84.0 mg / kg body weight; when the aglycone content ratio relative to the weight of the feed is 1.076 weight %, the aglycone intake each time in the first two months is approximately 753.2 to 860.8 mg / kg body weight, and the aglycone intake each time thereafter is approximately 269.0 mg / kg body weight. Moreover, when the genistein content ratio is 0.01 weight%, the genistein intake each time in the first two months is about 7 to 8 mg / kg body weight, and the genistein intake each time thereafter is about 2.5 mg / kg body weight; when the genistein content ratio is 0.031 weight%, the genistein intake each time in the first two months is about 21.70 to 24.8 mg / kg body weight, and the genistein intake each time thereafter is about 7.75 mg / kg body weight; when the genistein content ratio is 0.155 weight%, the genistein intake each time in the first two months is about 108.5 to 1,240 mg / kg body weight, and the genistein intake each time thereafter is about 38.75 mg / kg body weight.

Claims

1. A method for inducing feminization of eels, which is performed during the glass eel and / or baby eel stage. eels are fed with a feed for eels containing soybean isoflavones including genistein and containing 0.01% by weight or more of genistein in terms of dry matter. The eel feed contains 0.1% by weight or more of soybean isoflavone aglycones in terms of dry matter. in, The ratio in dry matter was calculated by setting the weight of the feed before preparation at the time of use as 100%.

2. The method for inducing eel feminization according to claim 1, wherein: Eels are fed an eel feed containing 0.05% by weight or more of soybean isoflavones in terms of dry matter.

3. The method for inducing eel feminization according to claim 1, wherein: Eels are fed an eel feed containing 0.2% by weight or more of soybean isoflavone aglycones in terms of dry matter.

4. The method for inducing eel feminization according to claim 1, wherein: The eel is an eel of Japanese eel.

5. A method for raising eels, which is a method for raising glass eels and / or young eels. eels are fed with a feed for eels containing soybean isoflavones including genistein and containing 0.01% by weight or more of genistein in terms of dry matter. The eel feed contains 0.1% by weight or more of soybean isoflavone aglycones in terms of dry matter. in, The ratio in dry matter was calculated by setting the weight of the feed before preparation at the time of use as 100%.

6. A method for producing female eels, comprising: a step of causing eels to ingest a feed for eels containing soybean isoflavones including genistein and containing 0.01% by weight or more of genistein in terms of dry matter, The eel feed contains 0.1% by weight or more of soybean isoflavone aglycones in terms of dry matter. in, The ratio in dry matter was calculated by setting the weight of the feed before preparation at the time of use as 100%.

7. The method for producing female eels according to claim 6, wherein: The standard feeding amount is 5-8% of the body weight for glass eels weighing 0.2g to 20g. When they are small eels weighing 20g to 30g, the standard feeding amount is 2-3% of the body weight, depending on the growth condition. Glass eels and / or baby eels are fed soy isoflavones continuously for 2 to 6 months to induce feminization. Eels are fed soy isoflavones for 3 to 7 days a week to induce feminization.

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