Eel farmed for consumption

Abstract

[Problem] To provide an edible cultured eel with high quality that has a high lipid content in the skeletal muscles.　[Solution] An edible cultured eel with high quality that has a high lipid content in the skeletal muscles, a group of edible cultured eels including such eel individuals, etc. The present invention includes an edible cultured eel, etc., said edible cultured eel satisfying formula I [wherein: X stands for the body weight (g) of the eel; and Z stands for the lipid / protein ratio] depending on the lipid content in the skeletal muscles of the eel. Even after growing up, the flesh of such eels is not toughened but high-level flesh tenderness and good quality and taste are maintained. (I): Z>-0.001X+1.95 (250<X<1,800)

Description

Technical Field

[0001] The present invention relates to high-quality edible cultured eels with a high degree of lipid content in skeletal muscle, and groups of edible cultured eels containing such eel individuals.

Background Art

[0002] Eels are a general term for fish belonging to the genus Anguilla of the family Anguillidae, and 19 species are known in the world, such as Japanese eel, giant eel, and European eel. Since ancient times, they have been used for food in regions such as Europe and East Asia, and especially in Japan, they have become a traditional and popular food ingredient.

[0003] For example, the Japanese eel (scientific name "Anguilla japonica") that inhabits the entire East Asia including Japan spawns near the Mariana Islands in the Pacific Ocean. After becoming larvae called leptocephalus, it transforms into glass eels that are almost transparent, about 5 to 6 cm in total length and 0.2 to 0.3 g in weight, and is thought to reach the coastal areas of the East Asian region by riding the Kuroshio current. Then, it settles and grows in land waters, coastal areas, brackish waters, etc. to become small eels (such as black eels), and is推测 to mature over another 5 to 10 years and migrate back towards the spawning grounds. Other eels may have different spawning and settlement locations, but generally have a similar life form.

[0004] Due to factors such as high demand and high profit, eel farming is widely carried out, and it is said that more than 99% of the total consumption is cultured eels. The current mainstream eel farming method is to capture natural glass eels that come to the coastal areas as fry for farming, release them into farming ponds for breeding, and grow them. Regarding complete farming that grows fry obtained from artificial incubation to adult eels and further obtains fry of the next generation, success has been reported at the laboratory level, but mass production at the commercial level has not been achieved.

[0005] Generally, male eels slow down in growth once they exceed 300g in weight, and their flesh becomes tougher, resulting in a decline in quality and taste. Female eels, on the other hand, have a greater growth limit than male eels; their growth does not slow down even beyond 300g, and their flesh remains tender, maintaining its quality and taste. However, when eels are raised in aquaculture environments from the glass eel stage to the juvenile stage, most of them become male, making it difficult to obtain female eels. Therefore, farmed eels for consumption are farmed and shipped on the assumption that they will be male. In other words, if they grow too large, their flesh becomes tough, their quality and taste decline, and they lose their commercial value, so farmed eels for consumption are usually shipped before they reach a weight of 250g.

[0006] It is known that feminization of eels can be induced by adding the female hormone (estradiol 17β) to compound feed during the period when eels grow from glass eels to juvenile eels. In addition, as a means of feminizing eels without using hormones, for example, Patent Document 1 describes a method of promoting feminization by raising eels before sexual differentiation in a tank equipped with a hollow containment member that completely covers the entire body of the eel that enters it.

[0007] Herein, we will explain soy isoflavones as a matter relating to the present invention.

[0008] Soy isoflavones are a general term for flavonoid compounds with isoflavones as their basic structure, mainly found in the germ of soybeans. Soy isoflavones are classified into four types: glycosides (structures covalently bonded to sugar), aglycones (non-glycosides; structures with the sugar portion removed from glycosides), acetylated glycosides, and malonylated glycosides. Three compounds are known in each classification, resulting in a total of 12 known compounds as soy isoflavones. Of these, the three glycoside soy isoflavones are genistin, daidzin, and glycitin, and their aglycone forms (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 soybean, extraction, purification, and processing methods. Furthermore, as a means of separating specific compounds in soy isoflavones, for example, Patent Document 2 discloses a method for separating high-purity genistein from an isoflavone mixture using a solvent.

[0009] Soy isoflavones have a chemical structure similar to the female hormone estrogen and are also called phytoestrogens. Furthermore, soy isoflavones in the aglycone form have estrogen-like effects and are believed to be effective in preventing heart disease, menopausal symptoms, osteoporosis, and breast cancer.

[0010] Furthermore, Non-Patent Document 1 states that when European eels were fed 2 mg / kg (dry feed) of genistein for 100 days, 55% became female, whereas when they were fed a higher amount of 20 mg / kg (dry feed), only 15% became female. [Patent Document 1] Japanese Patent Publication No. 2018-143182 [Patent Document 2] Japanese Patent Application Publication No. 7-173148 [Non-Patent Document 1] 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. [Disclosure of the Invention] [Problems that the invention aims to solve]

[0011] As mentioned above, when eels are raised in aquaculture environments from the glass eel stage to the juvenile eel stage, most of them become male eels. Male eels do not grow to a medium size or larger, and if they do grow, their flesh becomes tougher and their quality and taste deteriorate. Therefore, farmed eels sold for food in the market are mostly small, weighing around 200-250g, compared to wild eels that have grown in the natural environment and been caught for food, especially wild female eels. Furthermore, medium-sized and larger eels have a lower lipid content in their skeletal muscles, resulting in lower quality and taste.

[0012] On the other hand, because a technology for easily, safely, and stably producing female eels in aquaculture environments has not yet been established, it is currently not possible to mass-produce and supply to the market medium- and large-sized farmed eels for consumption that have a high lipid content in their skeletal muscles and are of good quality and taste.

[0013] Therefore, the present invention aims to provide high-quality farmed eels for food that are medium-sized or larger and have a high lipid content in their skeletal muscles. [Means for solving the problem]

[0014] The inventors have succeeded in easily and stably producing female eels in a farmed environment by feeding eels with eel feed supplemented with soy isoflavones during the glass eel and juvenile eel stages. As a result, they have achieved, for the first time, the production and mass production of high-quality farmed eels for food that are medium-sized or larger and have a high lipid content in their skeletal muscles.

[0015] Therefore, the present invention provides high-quality edible cultured eels of medium size or larger with a high degree of lipid content in skeletal muscle, and groups of edible cultured eels containing such eel individuals.

[0016] Depending on the degree of lipid content in eel skeletal muscle, the present invention includes edible cultured eels that satisfy the following formula I when the weight of the eel is X (g) and the lipid / protein ratio is Z. [Equation]

[0017] In addition, edible cultured eels having a weight greater than 250 g and satisfying the following formula II when the value according to the following formula A is defined as BMI, the BMI value is Y, and the lipid / protein ratio is Z are included. [Equation] [Equation]

[0018] Furthermore, edible cultured eels having a weight greater than 250 g and satisfying the following formula III when the gonad weight per unit weight is a (%) and the breaking load of the body during 10 minutes of heat processing is b (N) are included. [Equation]

[0019] During a predetermined period in the growth period from leptocephalus eels to small eels during cultivation, for example, during the period of undetermined sex or sexual plasticity, by allowing the eels to ingest eel feed added with soy isoflavones, it is possible to simply, efficiently, and stably produce female eels in a cultivation environment. As a result, it is possible to produce and mass-produce high-quality edible cultured eels of medium size or larger with a high ratio of adipose tissue in skeletal muscle.

[0020] In the present invention, "young eels" refer to those among juvenile eels that have grown more than whitebait eels. Hereinafter, for the sake of convenience, those with a weight of less than 0.5 g are regarded as whitebait eels, and those with a weight of 0.5 g or more are regarded as young eels.

Advantages of the Invention

[0021] According to the present invention, it is possible to provide high-quality edible cultured eels with a high degree of lipid content in skeletal muscle.

Best Mode for Carrying Out the Invention

[0022] <Edible Cultured Eels According to the Present Invention> The present invention broadly encompasses medium-sized or larger high-quality edible cultured eels with a high degree of lipid content in skeletal muscle.

[0023] The size of the edible cultured eels according to the present invention is medium-sized or larger. Specifically, the weight is preferably greater than 250 g, more preferably greater than 300 g, and most preferably greater than 350 g. Also, the weight of the eel is preferably less than 1,800 g, more preferably less than 1,500 g, and most preferably less than 1,200 g.

[0024] Further, the edible cultured eels according to the present invention include those with a weight within the above range and a high degree of lipid content in skeletal muscle. That is, even after growing to a weight greater than, for example, 250 g, the body does not become stiff, and the softness, quality, and taste of the body are well maintained.

[0025] In the present invention, it has also been newly found that there is a predetermined relationship between the weight of the eel and the lipid / protein ratio based on the degree of lipid content in the eel skeletal muscle. Based on this finding, the present invention includes edible cultured eels that satisfy the following formula I' when the weight of the eel is X (g) and the lipid / protein ratio is Z.

Number

[0026] In equation I', the range of the eel's weight X is as described above.

[0027] In formula I', the lipid / protein ratio Y can be obtained by known nutritional analysis methods. For example, skeletal muscle from the back and belly of an eel may be extracted, and the amount of protein and lipids may be measured by known nutritional analysis methods to calculate the lipid / protein ratio.

[0028] Furthermore, the present invention has newly discovered that there is a predetermined relationship between the BMI (body mass index) value and the lipid / protein ratio of eels, depending on the degree of lipid content in the eel skeletal muscle. Based on this finding, the present invention includes farmed eels for food that satisfy the following formula II' when the value given by formula A below is the BMI, the BMI value is Y, and the lipid / protein ratio is Z.

number

number

[0029] In formula II', the BMI value Y is preferably greater than 0.2, more preferably greater than 0.5, and most preferably greater than 0.8. Also, the BMI value Y is preferably less than 2.0, and more preferably less than 1.8. The lipid / protein ratio is the same as described above.

[0030] Furthermore, the present invention has newly discovered that there is a predetermined relationship between the degree of lipid content in the eel skeletal muscle and the breaking load of the flesh during heat processing. Based on this finding, the present invention includes farmed eels for food that satisfy the following formula III', where a (%) is the weight of the gonads per unit body weight and b (N) is the breaking load of the flesh during 10 minutes of heat processing.

number

[0031] The gonadal weight per unit body weight, i.e., the gonadal weight index a(%), can be calculated by a known method, for example, by extracting the gonads from an eel, measuring their weight, dividing by body weight, and multiplying by 100. In Equation III', the gonadal weight index a is preferably greater than 0.1%, and more preferably greater than 0.35%. Furthermore, the gonadal weight index a is preferably less than 4%, more preferably less than 3%, and most preferably less than 2%.

[0032] The breaking load b(N) of the eel during a 10-minute heat treatment is obtained as an indicator of the hardness of the eel after cooking and can be measured by a known method. For example, one side of the eel is cooked at an integrated temperature of 510,000 [°C·seconds], and then both sides are cooked. Cooking on one side may be done, for example, at 600 to 1,000°C for 510 to 850 seconds. An electric grill is preferred as the cooking equipment. After cooking, the breaking load b is measured on a specific part of the eel (such as the belly) using an elastic measuring device such as a rheometer.

[0033] In addition, in medium- and large-sized farmed eels, which have a high lipid content in their skeletal muscles, the adipose tissue in the skeletal muscles of the back or abdomen is localized in a reticular pattern.

[0034] Here, "a condition in which adipose tissue is localized in a reticular pattern" means that adipose tissue is deposited in an irregular reticular pattern throughout the muscle, and that the deposition rate is higher than that of a standard eel, and that the adipose tissue is fine-grained. Although the species is different, this corresponds to grades 4 and 5 of the meat quality grades set by the Japan Meat Grading Association as the beef carcass trading standards. In the eels targeted by this invention, this is particularly noticeable in the lateral muscles, and it can be said that those with an adipose tissue area ratio (adipose tissue area / total cross-sectional area) of 35% or more of the lateral muscles are eligible. Generally, the adipose tissue area ratio is higher in the ventral lateral muscles than in the dorsal muscles, and a ratio of 37% or more may be used as an indicator for the ventral lateral muscles.

[0035] The species of eel covered by this invention is not particularly limited, as long as it belongs to the genus Anguilla in the family Anguillidae. For example, the Japanese eel (scientific name "Anguilla japonica"), the giant eel (scientific name "Anguilla marmorata"), the European eel (scientific name "Anguilla anguilla"), and the American eel (scientific name "Anguilla rostrata") are also covered. In this invention, the Japanese eel is most preferred.

[0036] <Regarding the group of farmed eels for food according to the present invention> As described above, in aquaculture environments, most eels become male, so it is not possible for a certain proportion or more of medium-sized or larger edible farmed eels with a high lipid content in their skeletal muscles to be present in the market together. In other words, this invention makes it possible for the first time to have such edible farmed eels present in the market together, and this invention encompasses all groups formed by multiple such edible farmed eel individuals.

[0037] Considering that the occurrence rate of female eels in aquaculture environments is almost 0%, for example, a group of edible farmed eels formed with 10 or more individuals and containing 12% or more of the above-mentioned edible farmed eel individuals, more preferably a group containing 15% or more, and most preferably a group containing 25% or more, would be impossible to produce before the present invention and therefore would be included within the scope of the group of edible farmed eels according to the present invention.

[0038] <Regarding the production method of farmed eels and other edible fish according to the present invention> The production method for farmed eels and the like according to the present invention is not particularly limited. For example, these farmed eels and their groups may be produced and mass-produced by feeding them eel feed or eel feminization inducers, as described later, during the glass eel and / or juvenile eel stage. Furthermore, the present invention is not narrowly limited to those produced and mass-produced by the methods described below.

[0039] Eels undergo sexual differentiation at a specific stage during their growth from glass eels to juvenile eels (for example, during the growth period from 0.2g to 30g in weight). Once they reach a weight of 30g or more, it becomes possible to distinguish between males and females by morphological observation of the gonads. By feeding eels with eel feed or eel feminization inducers around the time of sexual differentiation, for example, during the glass eel and / or juvenile eel stage, feminization of eels can be reliably and efficiently induced. This makes it possible to produce and mass-produce high-quality farmed eels (or groups of eels) of medium size or larger with a high degree of lipid content in their skeletal muscles for consumption.

[0040] The means by which eels are given eel feed or eel feminization inducers are not particularly limited. For example, they may be given by feeding them, given separately, or administered directly to individual eels.

[0041] The period during which eels are given eel feed or eel feminization inducers is not particularly limited, as long as it includes the period of sex differentiation and the periods immediately before and after. For example, by continuously giving them these substances for 2 to 6 months during the glass eel and / or juvenile eel stage, it is highly likely that feminization of eels can be reliably and efficiently induced.

[0042] The frequency of feeding eel feed or eel feminization inducers is not particularly limited, as long as the feeding is continued uninterrupted throughout the feeding period. For example, feeding them for 3 to 7 days a week is likely to reliably and efficiently induce feminization in eels. Depending on the stage of eel growth, for example, during the glass eel to juvenile eel stage (e.g., weight 0.2g to 20g), the daily amount may be divided into 2 to 3 feedings, while during the juvenile eel stage (e.g., weight 20g to 30g), the daily amount may be given in a single feeding.

[0043] <About eel feed> In the production of farmed eels (or a group thereof) for food according to the present invention, eel feed can include, for example, a feed containing 0.05% by weight or more of soy isoflavones in dry matter proportion, a feed containing 0.05% by weight or more of soy isoflavone aglycones in dry matter proportion, or a feed containing 0.006% by weight or more of genistein in dry matter proportion.

[0044] By incorporating soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) into eel feed and feeding this feed to eels for a certain period during the glass eel and / or juvenile eel stage, feminization of eels can be induced. This makes it possible to produce and mass-produce high-quality farmed eels for food that are medium-sized or larger and have a high ratio of adipose tissue in their skeletal muscle.

[0045] Compound feed used for eels is often prepared by adding water, feed oil (fish oil), etc., mixing it into a paste, and then feeding it to the eels.

[0046] In this eel feed, the dry matter (hereinafter the same) should contain soy isoflavones in a proportion of 0.05% or more by weight, more preferably 0.2% or more by weight, and most preferably 1.0% or more by weight, when the weight of the feed before preparation (addition of water, etc.) is taken as 100%. There is no particular upper limit to the soy isoflavone content, but from the viewpoint of feed efficiency, 20% or less by weight is preferred, 8.0% or less by weight is more preferred, and 4.0% or less by weight is most preferred.

[0047] Soy isoflavones can be broadly selected from known sources and are not particularly limited. For example, commercially available products may be used, or those prepared by extraction, purification, and processing from raw materials such as soybeans using known methods may be used.

[0048] From another perspective, this eel feed should contain, in terms of dry matter, that is, when the weight of the feed before preparation (addition of water, etc.) is taken as 100%, soy isoflavone aglycone preferably at 0.05% by weight or more, more preferably at 0.2% by weight or more, and most preferably at 1.0% by weight or more. There is no particular upper limit to the soy isoflavone aglycone content, but from the viewpoint of feed efficiency, 20% by weight or less is preferred, 8.0% by weight or less is more preferred, and 4.0% by weight or less is most preferred. Note that "soy isoflavone aglycone" refers to the non-sugar portion of soy isoflavone (the same applies hereinafter), and its content weight can be obtained, for example, by converting it using the ratio of molecular weights of glycosides to aglycones from the weight of added soy isoflavones, or by analyzing it using known test methods.

[0049] From another perspective, this eel feed should contain genistein in proportion to the dry matter, that is, when the weight of the feed before preparation (addition of water, etc.) is taken as 100%, preferably 0.006% by weight or more, more preferably 0.02% by weight or more, and most preferably 0.1% by weight or more. There is no particular upper limit to the genistein content, but from the viewpoint of feed efficiency, 5.0% by weight or less is preferred, 2.0% by weight or less is more preferred, and 1.0% by weight or less is most preferred.

[0050] 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, or genistein may be directly added to eel feed, or soy isoflavones or genistein may be incorporated into the feed beforehand during the manufacturing process.

[0051] Genistein can be any known type and is not particularly limited. For example, commercially available products may be used, soy isoflavones containing genistein may be used as is, or genistein may be extracted, purified, and processed from soy isoflavones by known methods to separate or highly purify it, or genistein may be obtained from legumes or their processed products by known methods to separate, extract, and ferment, or it may be synthesized by known methods. For example, if the soy isoflavones contain 10% by weight or more of genistein, it is relatively easy to obtain, manufacture, and prepare, and it can reliably and efficiently induce feminization in eels, which has the advantage of enabling the production and mass production of high-quality farmed eels for food that are medium-sized or larger and have a high ratio of adipose tissue in skeletal muscle.

[0052] Furthermore, the term genistein used here broadly includes pharmacologically acceptable salts of genistein and derivatives of genistein, provided that they retain their feminizing effect on eels.

[0053] Eel feed only needs to contain at least soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds therein, such as genistein), and may contain other formulations and component compositions.

[0054] For example, the composition of eel feed, other than soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof), may be the same as that of commonly used compound feeds. Compound feed is a mixture of nutrients for eel growth in appropriate proportions, and may contain, for example, 50% or more by weight of fish meal on a dry matter basis, and may also contain starch, calcium phosphate, salt, yeast, herbal extracts, etc.

[0055] The fishmeal in the compound feed can be a wide variety of known types and is not particularly limited; for example, it may be powder obtained by processing sardines, mackerel, herring, horse mackerel, etc. It may also be fishmeal from other fish species, or a mixture of fishmeal from multiple fish species. The choice can be made appropriately considering the type of eel, its growth stage, cost, etc.

[0056] In addition, other ingredients that enhance the growth efficiency of eels, such as lactic acid bacteria, butyric acid bacteria, digestive enzymes, and dried vegetables, may be included as appropriate.

[0057] <About eel feminization inducers> In the production of edible farmed eels (or a group thereof) according to the present invention, eel feminization inducers can include, for example, those containing soy isoflavones as an active ingredient, administered at a rate of 10 mg / kg (eel body weight, the same applies hereinafter) or more per day; those containing soy isoflavone aglycones as an active ingredient, administered at a rate of 10 mg / kg or more per day; and those containing genistein as an active ingredient, administered at a rate of 1.2 mg / kg or more per day.

[0058] By incorporating soy isoflavones (or soy isoflavone aglycones, or one or more specific compounds thereof, such as genistein) as an active ingredient in an eel feminization inducer, and having eels ingest soy isoflavones during the glass eel and / or juvenile eel stage, feminization of eels can be reliably and efficiently induced. This makes it possible to produce and mass-produce high-quality farmed eels for food that are medium-sized or larger and have a high ratio of adipose tissue in skeletal muscle.

[0059] For compound feed, the general guideline for feeding amounts is 5-8% of body weight during the glass eel to juvenile eel stage (for example, when weighing around 0.2g-20g), and 2-3% of body weight during the juvenile eel stage (for example, when weighing around 20g-30g) as the eels grow. When the feed amount is 2% of body weight, it is preferable to provide at least 10mg / kg of soy isoflavones per day, more preferable to at least 40mg / kg, and most preferable to at least 200mg / kg. Furthermore, from the viewpoint of feed efficiency, when the feed amount is 8% of body weight, it is preferable to provide 16g / kg or less of soy isoflavones per day, more preferable to at least 6.4g / kg, and most preferable to at least 3.2g / kg.

[0060] For example, depending on the stage of eel growth, during the glass eel to juvenile eel stage (for example, when weighing approximately 0.2g or more but less than approximately 20g), soy isoflavones may be ingested at a rate of 25mg / kg to 16g / kg (eel weight) per day, more preferably 100mg / kg to 6.4g / kg, and most preferably 500mg / kg to 3.2g / kg. During the juvenile eel stage (for example, when weighing approximately 20g or more but less than approximately 30g), soy isoflavones may be ingested at a rate of 10mg / kg to 16g / kg (eel weight) per day, more preferably 40mg / kg to 6.4g / kg, and most preferably 200mg / kg to 3.2g / kg.

[0061] From another perspective, with this eel feminization inducer, it is preferable to administer 10 mg / kg or more of soy isoflavone aglycone per day, with the feed amount being 2% of body weight, more preferably 40 mg / kg or more, and most preferably 200 mg / kg or more. Furthermore, from the viewpoint of feed efficiency, with the feed amount being 8% of body weight, the intake of soy isoflavone aglycone per day is preferable to 16 g / kg or less, more preferably 6.4 g / kg or less, and most preferably 3.2 g / kg or less.

[0062] For example, depending on the stage of eel growth, the amount of soy isoflavone aglycone may be adjusted as follows: during the glass eel to juvenile eel stage (for example, when the eel weighs approximately 0.2g or more but less than approximately 20g), 25mg / kg to 16g / kg (eel weight) per day, more preferably 100mg / kg to 12g / kg, and most preferably 500mg / kg to 8g / kg; during the juvenile eel stage (for example, when the eel weighs approximately 20g or more but less than approximately 30g), 10mg / kg to 16g / kg (eel weight) per day, more preferably 40mg / kg to 6.4g / kg, and most preferably 200mg / kg to 3.2g / kg.

[0063] From another perspective, with this eel feminization inducer, it is preferable to administer genistein at a rate of 1.2 mg / kg or more per day, with a feed amount of 2% of body weight, more preferably 4.0 mg / kg or more, and most preferably 20 mg / kg or more. Furthermore, from the viewpoint of feed efficiency, with a feed amount of 8% of body weight, the genistein intake is preferable to 4.0 g / kg or less per day, more preferably 1.6 g / kg or less, and most preferably 0.8 g / kg or less.

[0064] For example, depending on the stage of eel growth, genistein may be administered at a rate of 3 mg / kg to 4.0 g / kg (eel weight) per day during the glass eel to juvenile eel stage (e.g., from approximately 0.2 g to less than approximately 20 g in weight), more preferably 10 mg / kg to 1.6 g / kg, and most preferably 50 mg / kg to 800 mg / kg. During the juvenile eel stage (e.g., from approximately 20 g to approximately 30 g in weight), genistein may be administered at a rate of 1.2 mg / kg to 1.5 g / kg (eel weight) per day, more preferably 4 mg to 600 mg / kg, and most preferably 20 mg / kg to 300 mg / kg.

[0065] Depending on the purpose, application, and dosage form, this eel feminization inducer may contain excipients, lubricants, binders, disintegrants, solvents, solubilizers, suspending agents, buffers, isotonic agents, preservatives, antioxidants, pH adjusters, dispersants, colorants, defoamers, and other appropriate additives.

[0066] Suitable examples of excipients include lactose, sucrose, D-mannitol, starch, crystalline cellulose, and light anhydrous silicic acid.

[0067] Suitable examples of lubricants include, for example, magnesium stearate, calcium stearate, talc, and colloidal silica.

[0068] Suitable examples of binders include, for example, crystalline cellulose, sucrose, D-mannitol, dextrin, hydroxypropylcellulose, hydroxypropylmethylcellulose, and polyvinylpyrrolidone.

[0069] Suitable examples of disintegrants include, for example, starch, carboxymethylcellulose, carboxymethylcellulose calcium, croscarmellose sodium, and carboxymethyl starch sodium.

[0070] Suitable examples of solvents include, for example, water for injection, alcohol, propylene glycol, macrogol, sesame oil, and corn oil.

[0071] Suitable examples of solubilizers include polyethylene glycol, propylene glycol, D-mannitol, benzyl benzoate, ethanol, trisaminomethane, cholesterol, triethanolamine, sodium carbonate, and sodium citrate.

[0072] Suitable examples of suspending agents include surfactants (such as stearyltriethanolamine, sodium lauryl sulfate, laurylaminopropionic acid, lecithin, benzalkonium chloride, benzethonium chloride, and glyceryl monostearate), hydrophilic polymers (such as polyvinyl alcohol, polyvinylpyrrolidone, sodium carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose).

[0073] Suitable examples of buffering agents include buffers such as phosphates, acetates, carbonates, citrates, tartrates, trishydroxymethylaminomethane, and HEPES.

[0074] Suitable examples of isotonic agents include, for example, sodium chloride, glycerin, and D-mannitol.

[0075] Suitable examples of preservatives include thimerosal, parahydroxybenzoic acid esters, phenoxyethanol, chlorobutanol, benzyl alcohol, phenethyl alcohol, dehydroacetic acid, sorbic acid, and various other preservatives, antibiotics, and synthetic antibacterial agents.

[0076] Suitable examples of antioxidants include, for instance, sulfites and ascorbic acid.

[0077] Suitable 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 trometamol; monoethanolamine; and diisopropanolamine.

[0078] Suitable examples of dispersants include sodium carboxymethylcellulose, hydroxypropyl methylcellulose, polyvinylpyrrolidone, and polysorbate 80.

[0079] Suitable examples of colorants include, for example, 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), Allura Red AC (Red No. 40), New Coccine (Red No. 102), Phloxine (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, and copper chlorophyllin sodium.

[0080] Suitable examples of defoaming agents include, for example, dimethicone, simethicone, silicone emulsion, sorbitan sesquioleate, and nonionic substances.

[0081] In addition to the above, this product may contain, as appropriate, auxiliary ingredients such as light-absorbing dyes (riboflavin, adenine, adenosine, etc.) that serve as preservatives and enhance efficacy, chelating and reducing agents (vitamin C, citric acid, etc.) for stabilization, carbohydrates (sorbitol, lactose, mannitol, starch, sucrose, glucose, dextran, etc.), casein digest, various vitamins, lactic acid bacteria, butyric acid bacteria, digestive enzymes, dried vegetables, etc. [Example 1]

[0082] In Example 1, we investigated whether soy isoflavones could induce feminization in eels.

[0083] Seventy glass eels (average weight 0.4g), whose sex was undetermined, were placed in 150L FRP tanks. They were fed a compound feed supplemented with soy isoflavones in various proportions until they were satisfied, and reared at a water temperature of 28°C.

[0084] The compound feed supplemented with soy isoflavones was administered five times a week. The amount of feed per feeding was 7-8% of body weight for the first two months, and approximately 2.5% of body weight thereafter.

[0085] Approximately six months after the start of rearing, individuals that had grown to weigh approximately 30g or more were sampled as needed, and their sex was determined.

[0086] Sex determination was performed by morphological observation of the gonads; those with ovaries were identified as female, and those with testes as male.

[0087] The results are shown in Tables 1 and 2. In each table, "Number of eels" represents the number of individual eels sampled; "Soy isoflavone addition rate" represents the percentage (by weight) of soy isoflavones added relative to the weight of the compound feed before soy isoflavone addition and preparation at the time of use (set as 100%); "Aglycone content rate" represents the percentage (by weight) of soy isoflavone aglycone content relative to the weight of the compound feed before soy isoflavone addition and preparation at the time of use (set as 100%); "Genistein content rate" represents the percentage (by weight) of genistein content relative to the weight of the compound feed before soy isoflavone addition and preparation at the time of use (set as 100%); and "Percentage of females" represents the percentage of females among the sampled individuals. Note that "Soy isoflavone aglycone content weight" represents the weight of the non-sugar portion of the added soy isoflavones, and analytical values ​​obtained based on known test methods were used. The "control" group, on the other hand, represents the results when the animals were fed a standard compound feed without added soy isoflavones. [Table 1] [Table 2]

[0088] As shown in Table 1, feminization of eels was induced by adding 1% or more soy isoflavones to eel feed during the glass eel to juvenile eel stage. Furthermore, as shown in Table 2, when eels were fed eel feed with an aglycone content of 0-0.040% by weight relative to the feed weight, all individuals differentiated into males. However, when the aglycone content was 0.100% or more by weight, 46% of individuals were feminized, when it was 0.336% by weight, 95% of individuals were feminized, and when it was 1.076% or more by weight, all individuals were feminized. From a different perspective, focusing on genistein contained in the feed due to the addition of soy isoflavones, when eels were raised on eel feed containing 0-0.004% by weight of genistein during the glass eel to juvenile eel stage, all individuals differentiated into males. However, when the genistein content was 0.01% by weight, 46% of individuals were feminized, and when it was 0.031% by weight, 95% of individuals were feminized. When the genistein content was 0.155% by weight or more, all individuals were feminized.

[0089] In this experiment, the amount of food given per feeding was 7-8% of body weight for the first two months, and then approximately 2.5% of body weight thereafter. Based on this calculation, if the soy isoflavone supplementation rate was 1% by weight, the amount of soy isoflavones consumed per feeding during the first two months was approximately 700-800 mg / kg body weight, and the amount of soy isoflavones consumed per feeding thereafter was approximately 250 mg / kg body weight. Similarly, when the aglycone content ratio to feed weight was 0.100% by weight, the aglycone intake per feeding for the first two months was approximately 70.0–80.0 mg / kg body weight, and the aglycone intake per feeding thereafter was approximately 25.0 mg / kg body weight. When the aglycone content ratio to feed weight was 0.336% by weight, the aglycone intake per feeding for the first two months was approximately 235.2–268.8 mg / kg body weight, and the aglycone intake per feeding thereafter was approximately 84.0 mg / kg body weight. When the aglycone content ratio to feed weight was 1.076% by weight, the aglycone intake per feeding for the first two months was approximately 753.2–860.8 mg / kg body weight, and the aglycone intake per feeding thereafter was approximately 269.0 mg / kg body weight. Furthermore, when the genistein content was 0.01% by weight, the average genistein intake per dose for the first two months was approximately 7-8 mg / kg body weight, and the average genistein intake per dose thereafter was approximately 2.5 mg / kg body weight. When the genistein content was 0.031% by weight, the average genistein intake per dose for the first two months was approximately 21.70-24.8 mg / kg body weight, and the average genistein intake per dose thereafter was approximately 7.75 mg / kg body weight. When the genistein content was 0.155% by weight, the average genistein intake per dose for the first two months was approximately 108.5-1,240 mg / kg body weight, and the average genistein intake per dose thereafter was approximately 38.75 mg / kg body weight. [Example 2]

[0090] In Example 2, male and female eels were compared based on their total length, body weight, and nutritional analysis.

[0091] The total length and body weight were measured for eels that were not feminized by soy isoflavones (male eels, n=7) and eels that were feminized by soy isoflavones (female eels, n=5). Furthermore, the BMI value was calculated for each individual using the formula A described above.

[0092] Next, skeletal muscle tissue from the back and abdomen was extracted, and nutritional analysis was performed to measure the protein and lipid content. The lipid / protein ratio in the skeletal muscle tissue from the back and abdomen was then calculated.

[0093] Figure 1 is a graph comparing body weight and lipid / protein ratio between males and females. In the figure, the horizontal axis represents body weight (g), and the vertical axis represents the lipid / protein ratio.

[0094] As shown in Figure 1, when the body weight of the eel is X (g) and the lipid / protein ratio is Z, the sex of farmed eels could be clearly distinguished using the following equation I'' as the boundary.

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[0095] Figure 2 is a graph comparing BMI values ​​and lipid / protein ratios between males and females. In the figure, the horizontal axis represents BMI values, and the vertical axis represents the lipid / protein ratio.

[0096] As shown in Figure 2, when the BMI value is Y and the lipid / protein ratio is Z, the sex of farmed eels could be clearly distinguished using the following equation II'' as the boundary.

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[0097] In Example 3, the gonadal weight index (GSI; gonadal weight / body weight) of eels feminized with soy isoflavones was calculated, and the relationship between the gonadal weight index and the firmness of the flesh after cooking was evaluated.

[0098] First, the body weight was measured for both male eels (n=12, body weight 200-350g) that were not feminized by soy isoflavones, and female eels (n=15, body weight 200-530g) that were feminized by soy isoflavones. In addition, the reproductive organs were removed and their weight was measured. The gonadal weight index was then calculated as the gonadal weight per unit of body weight (unit: %).

[0099] As a result, all male eels had a gonad weight of 0.35% or less per unit of body weight, while all female eels that were feminized with soy isoflavones had a gonad weight greater than 0.35% per unit of body weight.

[0100] Next, each eel was cut along the midline of its ventral side and opened up. Using an electric griller 3H-210 (manufactured by Higo Griller Co., Ltd.), each eel was heated at 850°C for 600 seconds on the skin side and 600 seconds on the flesh side to make plain grilled eel. After removing the skin, approximately 1 cm wide slices were made from three locations on the ventral side. For each of the three samples, a rheometer was used to measure the breaking load at the tip of the wedge-shaped attachment when cutting through the flesh, and the average value was used as an indicator of the flesh's hardness.

[0101] Figure 3 is a graph showing the relationship between the gonadal weight index and the breaking load of the ventral flesh after cooking. In Figure 3, the horizontal axis represents the gonadal weight index (GSI; gonadal weight per unit body weight; unit: %) of eels, and the vertical axis represents the breaking load of the ventral flesh after cooking (unit: N).

[0102] As shown in Figure 3, when the gonad weight index is a (%) and the breaking load of the ventral flesh after cooking is b (N), the sex of farmed eels could be clearly distinguished using the following equation III'' as the boundary.

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[0103] [Figure 1]A graph comparing body weight and lipid / protein ratio between males and females in Example 2. [Figure 2] A graph comparing BMI values ​​and lipid / protein ratio between males and females in Example 2. [Figure 3] A graph showing the relationship between the gonadal weight index and the breaking load of the ventral side of the fish after cooking in Example 3.

Claims

1. A group of 10 or more farmed eels for food, Weight 530g or less, and, A group of farmed eels for food in which 95% or more of the eels satisfy the following formula I, where X is the weight of the eel (g) and Z is the lipid / protein ratio. [Math 1]

2. A group of 10 or more farmed eels for food, If the weight is greater than 250g but less than or equal to 530g, A group of farmed eels for food in which 95% or more of the eels satisfy the following formula II, with Y being the BMI value calculated by formula A below and Z being the lipid / protein ratio. [Math 2] [Math 3]

3. A group of 10 or more farmed eels for food, If the weight is greater than 250g but less than or equal to 530g, A group of farmed eels for food containing 95% or more eels that satisfy the following formula III, where a (%) is the weight of the gonads per unit body weight and b (N) is the breaking load of the flesh during 10 minutes of heat processing. [Math 4]

4. The group of farmed eels for food according to any one of claims 1 to 3, wherein the adipose tissue in the skeletal muscle of the back or abdomen of the farmed eel for food is localized in a reticular pattern.

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