TW202437920A - Method for promoting the growth of eel, method for production of eel, and eel growth promoter - Google Patents

Abstract

The subject of the present invention is to provide a method for promoting the growth of slow-growing eels in the farming of edible eels. The present invention provides a method for promoting eel growth by feeding eel feed comprising soy isoflavones in a dry material with a ratio of 0.01% or more by weight to young eels. In the farming of edible eels, feeding soy isoflavones and the like to young eels can promote the growth of the eels. The present invention is particularly effective in promoting the growth of slow-growing eels. Therefore, the production efficiency of eel can be improved, the breeding period can be shortened, and the labor and cost required for breeding can be reduced.

Description

Eel growth promoting method, eel production method, and eel growth promoting agent

The present invention relates to a method for promoting the growth of eels by allowing young eels to ingest eel feed containing soybean isoflavones, etc., an eel production method including the steps, and an eel growth promoter containing soybean isoflavones, etc. as an effective ingredient.

Eel is a general term for fish belonging to the genus Eel of the family Eelidae. There are 19 known species in the world, including Japanese eel, white eel, and European eel. Eel has been eaten by humans in Europe and East Asia since ancient times, and is particularly popular as a traditional food in Japan.

For example, Japanese eels (scientific name "Anguilla japonica"), which grow throughout East Asia including Japan, are generally believed to spawn near the Mariana Islands in the Pacific Ocean. After becoming leaf-shaped larvae, they metamorphose into glass eels that are almost transparent, 5 to 6 cm in length, and weigh about 0.2 to 0.3 g. They then follow the Kuroshio Current to reach the coastal waters of East Asia. They then settle in inland waters, coastal waters, and soda waters and grow into small eels (such as black eels). They further spend five to ten years to mature and migrate to their spawning sites again. Although other eels have different spawning sites and settlements, they have almost the same lifestyle.

Farming eels is popular due to high demand and high profits. It is generally believed that more than 99% of the total consumption is farmed eels. The current mainstream eel farming method is to use natural glass eels that swim to coastal waters as breeding seedlings, release them into breeding ponds and raise them. In addition, although there are reports of experimental results on the complete breeding of artificially hatched fry into adult eels and further obtain the next generation of fry, it has not yet reached the stage of commercial mass production.

If glass eels are raised in a farm environment from the age of eels to young eels, they will almost always become male eels. Therefore, farmed eels for food are raised and shipped based on male eels. Generally speaking, male eels grow slowly when their weight exceeds 300g, and their meat becomes hard, which deteriorates their quality and taste. Therefore, farmed eels for food are usually shipped before their weight reaches 250g. In addition, the growth limit of female eels is greater than that of male eels. Even if the body weight exceeds 300g, it will not become blunt. The meat can be grown while maintaining its tenderness, and the quality and taste can be ensured. Therefore, compared with male eels, the commercial value of female eels is higher. However, as mentioned above, in the breeding environment, almost all eels will become male eels, so it is difficult to obtain female eels.

The following is a description of soy isoflavones related to the present invention.

Soy isoflavones are a general term for flavonoid compounds with isoflavones as the basic skeleton, which are mainly contained in soybean germs. Soy isoflavones can be classified into four types: glycoside type (glycoside; structure with covalent bond to sugar group), aglycone type (non-glycoside; structure with sugar group of glycoside partially detached), acetylated form of glycoside, and malonyl form of glycoside. There are three known compounds in each category, and a total of 12 known compounds of soybean isoflavones. Among them, the three types of soybean isoflavones of glycoside type are genistin, daidzin, and glycitin, and the aglycone type (the sugar part is separated) are genistein, daidzein, and glycitein. The composition and content of each compound will change depending on the type of raw material soybeans, extraction, purification, and processing methods. In addition, as a means of separating specific compounds in soybean isoflavones, for example, Patent Document 1 discloses a means of separating high-purity genistein from an isoflavone mixture using a solvent.

Soy isoflavones have a chemical structure similar to that of female hormones (estrogen), and are also called phytoestrogens. In addition, aglycon-type soy isoflavones have effects similar to estrogen and are generally believed to be effective in preventing heart disease, menopausal disorders, osteoporosis, breast cancer, etc.

In addition, Patent Document 2 discloses a method for inducing feminization of eels by ingesting soybean isoflavones, etc. In addition, Non-Patent Document 1 discloses that when carp is given 0, 25, 50, 100, 500, and 1000 mg of genistein per kg of feed, significant growth improvement is observed when 100 mg and 500 mg are given, and body composition or lipid metabolism is improved and immunity is enhanced. Non-Patent Document 2 discloses that when oval mullet is given 0, 10, 20, 40, 60, and 80 mg of soybean isoflavones per kg of feed, significant growth improvement is observed when 40 mg is given, and antioxidant capacity or immunity is enhanced. On the one hand, non-patent document 3 discloses that when yellowtails were given 2.5 g/kg of a feed containing 40% soybean isoflavones, their growth rate decreased and alkaline phosphatase in the blood increased (abnormalities in the liver, etc.), and non-patent document 4 discloses that when rainbow trout were given genistein at 0.3% relative to dry food feed, although the intake was reduced, protein utilization was improved, resulting in a growth rate at the same level as the control group. Even so, it was generally determined that the addition of genistein at 0.3% did not have a beneficial effect on the growth of rainbow trout. [Prior art document] [Patent document] Patent document 1: Japanese Patent Publication No. 7-173148. Patent document 2: Japanese Patent No. 6970992. [Non-patent literature] Non-patent literature 1: Liping Yang, et al “Evaluation of dietary genistein on the antioxidant capacity, non-specific immune status, and fatty acid composition of common carp (Cyprinus carpio .L)”  Aquaculture Volume 550, 15 March 2022, 737822. Non-patent literature 2: Chuanpeng Zhou, et al “The Effects of dietary soybean isoflavones on growth, innate immune responses, hepatic antioxidant abilities and disease resistance of juvenile golden pompano Trachinotus ovatus” Fish & Shellfish Immunology Volume 43, Issue 1, March 2015, Pages 158-166. Non-patent literature 3: Yajun Hu, et al “Effects of dietary soy isoflavone and soy saponin on growth performance, intestinal structure, intestinal immunity and gut microbiota community on rice field eel (Monopterus albus)” Aquaculture Volume 537, 15 May 2021, 736506. Non-patent document 4: C. Torno, et al “Effects of resveratrol and genistein on growth, nutrient utilization and fatty acid composition of rainbow trout” Animal Volume 13, Issue 5, 2019, Pages 933-940.

[The problem that the invention wants to solve]

For example, when glass eels are released into a breeding pond and raised, the growth rate often varies. Some eels grow to a shipping grade in a relatively short period of time, while a large number of slow-growing eels are produced. If there are more slow-growing eels, the production efficiency of the eel at the breeding site will be reduced, and the breeding period will be prolonged, which will increase labor and cost. Therefore, from the perspective of production efficiency, labor and cost, it is important to promote the growth of slow-growing eels.

Therefore, the present invention aims to provide a means for promoting the growth of slow-growing eels in edible eel farming. [Means for solving the problem]

The present invention provides a method for promoting the growth of eels by allowing young eels to ingest eel feed containing soybean isoflavones.

In edible eel farming, allowing young eels to ingest soy isoflavones and other substances can promote the growth of eels.

The present invention is particularly effective in promoting the growth of slow-growing eels. If many slow-growing individuals are produced in edible eel farming, the production efficiency of the eels will be reduced, the farming period will be prolonged, and the labor and cost required for farming will increase. In contrast, the present invention can promote the growth of slow-growing eels, thereby improving the production efficiency of eels and shortening the farming period, thereby reducing the labor and cost required for farming.

In addition, in the present invention, "juvenile eels" refer to glass eels and more grown eels. For convenience, those weighing less than 0.5g are called glass eels, and those weighing 0.5g to 20g are called eels. Juvenile eels include both. [Effects of the invention]

According to the present invention, the growth of eels can be promoted in edible eel farming, and the invention is particularly effective in promoting the growth of eels that grow slowly in edible eel farming.

<Eel feed of the present invention> The present invention broadly includes: an eel feed containing 0.01% by weight or more of soy isoflavone in dry matter, an eel feed containing 0.01% by weight or more of soy isoflavone aglycone in dry matter, and an eel feed containing 0.002% by weight or more of genistein in dry matter, etc.

Eel feed contains soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein, etc.), and the eel growth can be promoted by feeding the feed to juvenile eels (e.g., with a body weight of about 0.2 g to 20 g) at a fixed period.

Most eel feeds are mixed with water, feed oil (fish oil), etc., and then mixed into a paste before being fed to eels.

In the present invention, the soy isoflavones are preferably contained in an amount of 0.01% by weight or more, more preferably 0.05% by weight or more, and most preferably 0.1% by weight or more, in terms of the ratio in dry matter (dry matter, the same below), that is, when the weight of the feed before preparation (adding water, etc.) at the time of use is set to 100%. Although the upper limit is not particularly limited, if the content ratio of soy isoflavones is higher, it will almost completely induce estrogenation depending on the intake period, so it is preferably, for example, 4.0% by weight or less.

Soy isoflavones can be any known ones without particular limitation. For example, a finished product can be used, or one extracted, purified, processed and prepared from raw materials such as soybeans by known methods can be used.

From another point of view, in terms of the proportion in dry matter, that is, when the weight of the feed before preparation (adding water, etc.) at the time of use is set to 100%, the soybean isoflavone aglycone preferably contains 0.01% by weight or more, more preferably 0.05% by weight or more, and most preferably 0.1% by weight or more. Although the upper limit is not particularly limited, if the content ratio of soybean isoflavone aglycone is higher, almost all of them will be induced to be estrogenized due to different intake periods, so it is preferably, for example, 4.0% by weight or less. In addition, "soybean isoflavone aglycone" is the non-sugar part of soybean isoflavone (the same below), and its content weight can be obtained, for example, by converting the weight of the added soybean isoflavones with the molecular weight ratio of glycosides and aglycones, and can also be obtained by analysis by known test methods. In addition, the isoflavone aglycones of the present invention may include components obtained by chemically treating isoflavone aglycones, such as hydroxylated isoflavones (dihydroxyisoflavones), as long as they are derived from soybeans and can maintain the growth-promoting effect on eel.

From another point of view, in terms of the ratio in dry matter, that is, when the weight of the feed before preparation (addition of water, etc.) is set as 100%, genistein preferably contains 0.002% by weight or more, more preferably 0.01% by weight or more, and most preferably 0.02% by weight or more. Although the upper limit is not particularly limited, if the content ratio of genistein is higher, almost all of the genistein will be induced to be estrogenized depending on the intake period, so it is preferably, for example, 0.8% by weight or less.

The method of adding genistein to eel feed is not particularly limited. For example, genistein may be added to eel feed by adding soybean isoflavones containing genistein to eel feed, genistein may be directly added to eel feed, or soybean isoflavones or genistein may be added in advance during feed production.

Genistein can be a known product without any particular limitation. For example, a finished product can be used, or soybean isoflavones containing genistein can be used directly, or soybean isoflavones extracted, refined, processed, separated or highly purified by a known method can be used, or beans or processed products thereof can be separated, extracted, fermented, etc. by a known method can be used, or those synthesized by a known method can be used. For example, when the aforementioned soybean isoflavones contain 10% by weight or more of genistein, it has the advantages of being easier to obtain, manufacture, and prepare, and can effectively promote the growth of eels.

Furthermore, as long as the growth promoting effect relative to eel is maintained, the genistein of the present invention may include its pharmacologically acceptable salts and genistein derivatives.

The eel feed of the present invention only needs to contain at least soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein), and is not narrowly limited by other blends, ingredient compositions, etc.

For example, in eel feed, the blending and composition other than soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof) can be the same as those of commonly used mixed feed. Mixed feed is a mixture of nutrients suitable for eel growth in appropriate proportions, for example, it can contain more than 50% by weight of fish meal in dry matter ratio and further contain starch, calcium phosphate, salt, yeast, herbal extracts, etc.

The fish meal in the mixed feed can be any known one and is not particularly limited. For example, it can be powder obtained by processing sardines, mackerel, herring, tuna, etc. It can also be fish meal of other fish species or a mixture of fish meal of multiple fish species. It can be appropriately selected in consideration of the type of eel, growth status, cost, etc.

In addition, ingredients that improve the reproductive efficiency of eels, such as lactic acid bacteria, Clostridium butyricum, digestive enzymes, and dried vegetables, may be appropriately contained.

<Eel growth promoter of the present invention> The present invention includes: (1) an eel growth promoter containing soybean isoflavones as an active ingredient, which allows juvenile eels to ingest 5 mg/kg (eel body weight) or more per day; (2) an eel growth promoter containing soybean isoflavone aglycones as an active ingredient, which allows juvenile eels to ingest 5 mg/kg (eel body weight) or more per day; and (3) an eel growth promoter containing genistein as an active ingredient, which allows juvenile eels to ingest 0.625 mg/kg (eel body weight) or more per day.

The eel growth promoter of the present invention contains soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) as an active ingredient. The eel growth can be promoted by feeding the growth promoter to juvenile eels (e.g., with a body weight of about 0.2 g to 20 g) at a fixed period.

Mixed feed is generally fed to satiety. The amount of feed at this time can be about 5-10% of the body weight of juvenile eels (e.g., weighing about 0.2g-20g).

At this time, for example, during the period of young eels (e.g., body weight of about 0.2g to 20g), the feeding amount of mixed feed can be 5 to 10% of body weight, and the daily intake of soybean isoflavones is preferably 5 mg/kg (eel body weight) or more, more preferably 25 mg/kg or more, and most preferably 50 mg/kg or more. There is no particular upper limit, but if the content of soybean isoflavones is higher, it will almost completely induce feminization depending on the intake period, so for example, it is preferably less than 2,000 mg/kg.

On the other hand, when eels are young (e.g., weighing about 0.2g to 20g), the amount of mixed feed fed is 5 to 10% of their body weight, and the daily intake of soybean isoflavone aglycones is preferably 5 mg/kg (eel body weight) or more, more preferably 25 mg/kg or more, and most preferably 50 mg/kg or more. There is no particular upper limit, but if the content of soybean isoflavone aglycones is higher, it will almost completely induce feminization depending on the intake period, so for example, it is preferably below 2,000 mg/kg.

On the other hand, during the period of young eels (e.g., body weight of about 0.2g~20g), the feeding amount of mixed feed can be 5~10% of body weight, and the daily intake of genistein is preferably 0.625mg/kg (eel body weight) or more, more preferably 3.125mg/kg or more, and most preferably 6.25mg/kg or more. There is no particular upper limit, but if the content of genistein is higher, it will almost completely induce feminization depending on the intake period, so for example, it is preferably below 250mg/kg.

The eel growth promoter of the present invention may be appropriately added with a sizing agent, a lubricant, a binder, a disintegrant, a solvent, a dissolution aid, a suspending agent, a buffer, a tonic agent, a preservative, an antibacterial agent, an antioxidant, a pH adjuster, a dispersant, a colorant, a defoaming agent, etc., depending on the purpose, use, dosage form, etc.

Preferred examples of the excipient include lactose, white sugar, D-mannitol, starch, crystalline cellulose, light silicic anhydride, and the like.

Preferred examples of lubricants include magnesium stearate, calcium stearate, talc, colloidal silica, and the like.

Preferred examples of the binder include crystalline cellulose, white sugar, D-mannitol, dextrin, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, polyvinyl pyrrolidone, and the like.

Preferred examples of disintegrants include starch, carboxymethyl cellulose, calcium carboxymethyl cellulose, cross-linked sodium carboxymethyl cellulose, sodium carboxymethyl starch, and the like.

Preferred examples of the solvent include water for injection, alcohol, propylene glycol, polyethylene glycol, sesame oil, corn oil, and the like.

Preferred examples of the dissolution aid include polyethylene glycol, propylene glycol, D-mannitol, benzyl benzoate, ethanol, triaminomethane, cholesterol, triethanolamine, sodium carbonate, sodium citrate, and the like.

Preferred examples of the suspending agent include surfactants (stearyl triethanolamine, sodium lauryl sulfate, lauryl aminopropionic acid, lecithin, benzyl ammonium chloride, benzathonine chloride, glyceryl monostearate, etc.), hydrophilic polymers (polyvinyl alcohol, polyvinyl pyrrolidone, sodium carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), etc.

Preferred examples of the buffer include phosphate, acetate, carbonate, citrate, tartrate, trihydroxymethylaminomethane, HEPES and the like buffer solutions.

Preferred examples of tonic agents include sodium chloride, glycerol, and D-mannitol.

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

Preferred examples of antioxidants include sulfites and ascorbic acid.

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 bicarbonates such as sodium carbonate, alkali metal acetates such as sodium acetate, alkali metal citrates such as sodium citrate, bases such as trihydroxymethylaminomethane, monoethanolamine, and diisopropanolamine.

Preferred examples of the dispersant include sodium carboxymethylcellulose, hydroxypropylmethylcellulose, polyvinylpyrrolidone, polysorbate 80, and the like.

Preferred examples of coloring agents include caramel color, agarwood color, anthocyanin color, carmine color, capsicum color, safflower color, red yeast rice color, carotene color, carotenoid color, flavonoid color, cochineal color, amaranth (red No. 2), erythrorhizon (red No. 3), temptation red AC (red No. 40), new carmine (red No. 102), rose red (red No. 104), Bengal rose (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, sodium copper chlorophyllide, etc.

Preferred examples of defoaming agents include silicone, simethicone, polysilicone emulsion, sorbitan sesquioleate, non-ionic substances, and the like.

In addition, the agent may contain appropriate supplementary ingredients, such as light-absorbing pigments (riboflavin, adenine, adenosine, etc.) that aid preservation/performance, chelating agents that aid stabilization, reducing agents (vitamin C, citric acid, etc.), carbohydrates (sorbitol, lactose, mannitol, starch, sucrose, glucose, polyglucose, etc.), casein digests, various vitamins, lactic acid bacteria, Clostridium butyricum, digestive enzymes, dried vegetables, etc.

<Method for promoting growth of eel of the present invention> The present invention includes: (1) a method for promoting growth of eel of the present invention, wherein juvenile eels are fed with a feed containing 0.01% by weight or more of soybean isoflavones in dry matter; (2) a method for promoting growth of eel of the present invention, wherein juvenile eels are fed with a feed containing 0.01% by weight or more of soybean isoflavone aglycones in dry matter; (3) a method for promoting growth of eel of the present invention, wherein juvenile eels are fed with a feed containing 0.002% by weight or more of genistein in dry matter; (4) A method for promoting the growth of eels by allowing young eels to take in 5 mg/kg (eel body weight) or more of soy isoflavones per day; (5) a method for promoting the growth of eels by allowing young eels to take in 5 mg/kg (eel body weight) or more of soy isoflavone aglycones per day; and (6) a method for promoting the growth of eels by allowing young eels to take in 0.625 mg/kg (eel body weight) or more of genistein per day, etc.

For example, eel feed containing soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) in the above-mentioned ratio can be ingested at a fixed period during the period of young eels (e.g., body weight of about 0.2 g to 20 g), or from another point of view, soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) within the above-mentioned intake range can be ingested at a fixed period, thereby promoting the growth of eels.

For example, juvenile eels may be given 5mg/kg to 2,000mg/kg (eel body weight) of soy isoflavones daily for a fixed period of time, preferably 25mg/kg to 2,000mg/kg, and most preferably 50mg/kg to 2,000mg/kg.

On the other hand, young eels should be given 5mg/kg~2,000mg/kg (eel body weight) of soybean isoflavone aglycones daily for a fixed period of time, preferably 25mg/kg~2,000mg/kg, and most preferably 50mg/kg~2,000mg/kg.

On the other hand, juvenile eels are given a daily intake of 0.625 mg/kg to 250 mg/kg (eel body weight) of genistein for a fixed period of time, preferably 3.125 mg/kg to 250 mg/kg, and most preferably 6.25 mg/kg to 250 mg/kg.

The means of ingesting soybean isoflavones and the like are not particularly limited. For example, it can be done by feeding eels with feed containing soybean isoflavones and the like, or by ingesting soybean isoflavones and the like separately from the feed, or by directly administering a preparation of soybean isoflavones and the like to an individual eel.

The intake period of soy isoflavones, etc. is not particularly limited as long as the soy isoflavones, etc. can be taken during a fixed intake period, and can be appropriately adjusted according to the growth rate of the eel, etc. For example, the soy isoflavones, etc. can be taken continuously for 10 days to 6 months in the period of young eels (e.g., body weight of about 0.2g to 20g) according to the growth rate of the eel, etc.

The frequency of intake of soybean isoflavones and the like is not particularly limited as long as it can be taken continuously during the intake period. For example, taking soybean isoflavones and the like 3 to 7 days a week can effectively promote the growth of eels. In addition, for example, the daily intake can be given once or divided into 2 to 3 times.

The present invention includes the promotion of growth by ingesting soybean isoflavones etc. for young eels that are undifferentiated, ambiguous, or differentiated in sex, and is not narrowly limited to the subject due to the distinction between male and female. However, as mentioned above, it is known that eels will be induced to feminize if they ingest soybean isoflavones etc. (Patent Document 2). In the case of individuals induced to feminize, it is difficult to clearly distinguish which mechanism of the two, feminization induction and growth promotion achieved by ingesting soybean isoflavones etc., is more effective. On the other hand, for male individuals (other than those determined to be female or feminized after growth), ingesting soybean isoflavones etc. can unilaterally promote the growth of eels, so it can be clearly distinguished as growth promotion in the present invention. Therefore, for example, the subjects can be limited to juvenile eels that exclude those that are judged as female or feminized after growth, thereby determining whether the present invention has the effect of utilization. Growth promotion in the present invention is presumed to be achieved by a mechanism different from inducing feminization. If growth is promoted and there are male individuals (non-feminized individuals) after growth, it can be considered that the growth promotion mechanism is more effective in this individual than inducing feminization. For example, in a specific breeding site, the number of eels that have not reached the shipping grade size (e.g., 200 g or more) after 1 year and 6 months from the introduction of glass eels can be reduced to less than 50% of previous years, and there are male individuals among them. This situation is not within the scope of the known technology, and if it were not for the use of the present invention, this situation would not occur. Therefore, the fact that such a situation actually occurred is evidence of the efficacy of the present invention. In addition, it is difficult to distinguish between males and females if the eels do not grow to a certain size, but after they grow, they can be distinguished between males and females by known technology.

<Eel production method of the present invention> The present invention includes: (1) an eel production method for allowing young eels to ingest an eel feed containing 0.01% by weight or more of soybean isoflavones in dry matter; (2) an eel production method for allowing young eels to ingest an eel feed containing 0.01% by weight or more of soybean isoflavone aglycones in dry matter; (3) an eel production method for allowing young eels to ingest an eel feed containing 0.002% by weight or more of genistein in dry matter; (4) an eel production method for allowing young eels to ingest 5 mg/kg (eel body weight) of soybean isoflavones per day; (5) A method for producing eels that allows young eels to ingest 5 mg/kg (eel body weight) or more of soybean isoflavone aglycones per day; and (6) a method for producing eels that allows young eels to ingest 0.625 mg/kg (eel body weight) or more of genistein per day, etc.

As mentioned above, for example, the step of allowing young eels to ingest eel feed containing soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) in the above-mentioned ratio may be included, or from another point of view, the step of ingesting soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) within the above-mentioned intake amount range may be included, thereby promoting the growth of eels, and as a result, the production efficiency of eels can be improved.

The content ratio or intake amount, means, period, frequency, time period, etc. of soybean isoflavones (or soybean isoflavone aglycones, or one or more specific compounds thereof, such as genistein) are the same as those described above.

Furthermore, the eel species of the present invention are not particularly limited as long as they belong to the genus Anguilla of the family Anguilla. For example, the eel species include Japanese eel (scientific name "Anguilla japonica"), white eel (scientific name "Anguilla marmorata"), European eel (scientific name "Anguilla anguilla"), American eel (scientific name "Anguilla rostrata"), bicolor eel (scientific name "Anguilla bicolor bicolor"), etc. In the present invention, the eel is preferably Japanese eel.

(Example 1) In Example 1, the growth of glass eels was investigated when they ingested soybean isoflavones.

Glass eels (total weight at introduction: 20.0 kg, average weight: 0.20 g) were introduced into wild freshwater eel aquaculture ponds and acclimated. Glass eels that had grown to an average weight of 0.33 g were fed a mixed feed supplemented with soy isoflavones for 40 days. They were then fed a normal mixed feed for the next 6 to 8 months. In addition, the same number of glass eels (total weight at introduction: 20.0 kg, average weight: 0.20 g) in the control group were fed only a mixed feed without soy isoflavones added, and were raised for the same period and under the same conditions.

The mixed feed is fed once a day, and the amount of feed is adjusted to the degree of satiation of the glass eel. In the early stage of rearing, 5-10% of the weight of the glass eel is fed, and the feeding amount is gradually reduced according to the satiation status, and it is about 1% of the weight at the end of rearing.

When the weight of the mixed feed before adding soy isoflavones and before preparation is taken as 100%, the amount of soy isoflavones added to the mixed feed to which soy isoflavones are added is 0.4% by weight. In addition, the soy isoflavones used contain about 40% by weight of genistein, so when the weight of the mixed feed before adding soy isoflavones and before preparation is taken as 100%, the amount of genistein in the mixed feed to which soy isoflavones are added is about 0.16% by weight.

In this experiment, when the glass eels were fed only a mixed feed without soy isoflavones added and raised, the total weight of the eels at the time of introduction was 20.0kg, and after the raising period, the total weight of the eels grew to 12,115kg, and the weight gain rate during this period was 606 times. In contrast, when the glass eels were fed a mixed feed with soy isoflavones added and raised, the total weight of the eels grew to 15,227kg after the raising period, and the weight gain rate during this period increased to 761 times. In addition, visual observation of eels fed a mixed feed supplemented with soy isoflavones revealed that the number of eels that grew particularly slowly decreased, the degree of inconsistency in growth decreased, the size of the eels became more uniform, and the number of eels that did not reach shipping grade, i.e., a size of 200 g or more, within a fixed period of time, also decreased.

In addition, 10 glass eels that were randomly caught and raised on a mixed feed without added soy isoflavones were sexed, and the female rate was 0%. On the other hand, 50 glass eels that were randomly caught and raised on a mixed feed with added soy isoflavones were sexed, and the female rate was 16%.

These results show that the weight gain rate of glass eels can be increased and the growth of glass eels can be significantly promoted by allowing them to ingest soybean isoflavones. In addition, it can be found that the growth of individuals that grow slower than other individuals can be promoted.

In addition, the amount of each feeding during the period of feeding the mixed feed supplemented with soy isoflavones was 5-10% by weight of the glass eel body weight, and the amount of soy isoflavones added to the mixed feed was 0.4% by weight. Based on this conversion, the soy isoflavone intake of one individual in this experiment was approximately 200-400 mg/kg body weight, and the genistein intake of one individual was approximately 50-160 mg/kg body weight.

(Example 2) As disclosed in the above-mentioned patent document 2, when glass eels ingest an appropriate amount of soybean isoflavones, the eels can be induced to feminize. Therefore, in Example 2, the relationship between the growth promotion of glass eels when ingesting soybean isoflavones as shown in Example 1 and the induction of feminization of eels is investigated.

Glass eels with an average body weight of 0.20 g were introduced into a wild freshwater eel breeding pond and acclimated, and fed with a general mixed feed to a full state and cultured. Then, the glass eels that grew to an average body weight of 0.33 g were fed with a mixed feed to which soy isoflavones were added to a full state until their body weight reached about 3 g, and then returned to a general mixed feed without soy isoflavones added to be cultured to a full state. The soy isoflavones used were the same as those in Example 1, and the amount of soy isoflavones added to the mixed feed to which soy isoflavones were added was 0.25% by weight, taking the weight of the mixed feed before the addition of soy isoflavones and before preparation at the time of use as 100%. In the control group, the same glass eels were fed only with a normal mixed feed without added soy isoflavones during the entire period, and were raised under the same conditions for the same period of time.

The results showed that when the glass eels were fed only a mixed feed without added soy isoflavones (control group), the average body weight was 24.0g (n=30) 3 months after introduction into the breeding pond. In contrast, when the glass eels were fed a mixed feed with added soy isoflavones for a fixed period of time, the average body weight was 29.2g (n=30) 3 months after introduction into the breeding pond, indicating a growth promotion of about 1.22 times compared to the control group. Furthermore, when sex determination was performed, the female ratio of glass eels that were raised on a mixed feed without added soy isoflavones (control group) was 0% (all 30 examined were male). In contrast, among the glass eels that were raised on a mixed feed with added soy isoflavones for a fixed period of time, 11 of the 30 examined were males, 14 were females, and 5 were other, for a female ratio of 33%.

The body weights of glass eels (11 males and 14 females) that were fed a mixed feed supplemented with soy isoflavones for a fixed period of time were measured. The average body weight of males was 30.4 g (standard deviation 4.6 g), and the average body weight of females was 28.0 g (standard deviation 4.1 g).

As mentioned above, when only males were compared, the average body weight increased from 24.0g to 30.4g in the case of adding soy isoflavones and not adding soy isoflavones, which confirmed the growth promotion brought about by the addition of soy isoflavones. In addition, when soy isoflavones were added, there was no significant growth difference between males and females. From this, it can be inferred that the growth promotion effect of soy isoflavones is caused by a mechanism different from that of inducing feminization.

(Example 3) As mentioned above, in eel farming sites, there are usually many individuals that grow slowly and have not grown to shipping size after one year (eels farmed for more than one year), which will reduce the production efficiency of eels. Therefore, in Example 3, the growth-promoting effect of soybean isoflavones on these slow-growing individuals was verified.

The eels were caught from December 2021 to April 2022 and raised in wild eel freshwater aquaculture ponds for about a year, but the average weight only reached 11.0 g. The eels were fed a mixed feed supplemented with soy isoflavones in a saturated manner in a freshwater aquaculture pond for 54 days. The soy isoflavones used were the same as those in Example 1, etc., and the amount of soy isoflavones added to the mixed feed supplemented with soy isoflavones was 0.25% by weight when the weight of the mixed feed before the addition of soy isoflavones and before the preparation at the time of use was 100%.

The results showed that the average body weight of individuals that only reached 11.0g (n=60) in about one year increased to 19.3g (n=60) after 54 days of feeding on a mixed feed supplemented with soy isoflavones, which is about 1.8 times the growth rate. The feminization rate was 22%. This result shows that soy isoflavones have a growth-promoting effect on individuals that grow more slowly.

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Claims (9)

A method for promoting the growth of eels is to allow young eels to ingest eel feed containing soy isoflavones. A method for promoting the growth of eels is to allow young eels to ingest eel feed containing soy isoflavone aglycone. The method for promoting eel growth as described in claim 1, comprising soybean isoflavones containing genistein. The method for promoting eel growth as described in claim 3, wherein the ratio of the aforementioned genistein contained in the dry matter is 0.002% by weight or more. The method for promoting eel growth as described in claim 1 is to allow young eels to ingest eel feed containing soybean isoflavones, wherein the young eels do not include individuals that are determined to be female or feminized after growth. The eel growth promotion method as described in claim 1, wherein the eel is Japanese eel. A method for producing eels includes the step of allowing young eels to ingest eel feed, wherein the eel feed contains soybean isoflavones at a ratio of 0.01% by weight or more in dry matter. A growth promoter for eels, which allows juvenile eels to take in 5 mg/kg (eel body weight) or more per day and contains soybean isoflavones as an active ingredient. A growth promoter for eels, which allows juvenile eels to take in 0.625 mg/kg (eel body weight) or more per day and contains genistein as an active ingredient.