JP7709488B2 - Yellowtail farmed fish - Google Patents

Description

The present disclosure relates to farmed yellowtail fish.

Yellowtail is generally known as a fish that is in season in the winter, and from the perspective of preserving natural resources and controlling quality, not only wild yellowtail but also farmed yellowtail is in circulation.
It is generally known that when yellowtails reach maturity and reach spawning age, they lose nutrients to their eggs around the time of spawning, causing them to lose weight. For this reason, in many cases, growth slows and fat content decreases during or after the spawning season in February to April for wild yellowtails and in May to June for farmed yellowtails, resulting in a decrease in commercial value. For this reason, various techniques are being studied to reduce the effects of growth slowdown and leanness in farmed yellowtails.

Patent Document 1 provides a farming method that allows fish to steadily mature without any stagnation or decline in growth due to maturation of reproductive organs and spawning and sperm release organs, and does not delay shipment. Specifically, the method discloses a farming method for raising yellowtail and other fish, in which electric lights with a constant illuminance are turned on from evening until the following morning, from October to May of the following year at the latest. It states that with this method, the growth of the fish's reproductive organs is almost completely suppressed, spawning and release of sperm into the water do not occur, and the fish continue to grow even during this period.

Patent Document 2 describes a fish feed containing 90 mg or less of vitamin E per kg and at least one antioxidant selected from the group consisting of coenzyme Q10, sesaminol, alpha lipoic acid, and astaxanthin, and states that the use of this fish feed can suppress growth stagnation caused by reproductive activity in fish.

Non-Patent Document 1 also discloses that restricting feed intake from winter to spring until just before the breeding season increases body weight compared to unrestricted groups, and suppresses reproductive gland development in yellowtail during the breeding season.

JP 2003-333953 A JP 2013-188207 A

Aquaculture, 424-425 (2014) 10-17

However, the commercial value of yellowtail depends in part on its size. If the body weight is suppressed before the maturation of the reproductive organs, or if the body weight is reduced to around 3 kg after the maturation of the reproductive organs, it cannot be said that the commercial value is sufficient.
Furthermore, if the goal is to maintain the good characteristics of farmed fish and continue farming them, maturation of the reproductive organs is essential, so farmed fish in which the maturation of the reproductive organs is completely suppressed will lose their sustainability as a farm.

Therefore, an object of the present disclosure is to obtain farmed yellowtail fish that are less likely to lose weight after the maturation of their reproductive organs and have excellent sustainability.

The present disclosure includes the following.
<1> Raising Seriola spp. fish in a regulated rearing environment for at least two months, and then starting rearing using Seriola spp. fish larvae obtained by artificially collecting eggs, thereby growing Seriola spp. fish;
Obtaining a mature cultured fish of the genus Yellowtail, which is a male individual having a gonadosomatic index (GSI) of 0.5% to 10.0% or a female individual having a GSI of 0.5% to 4.5% at the maturity stage of reproductive organs, and has a body fatness index of 18 or more and a body weight of 3.5 kg or more;
A method for raising farmed fish of the genus Seriola includes obtaining, from the obtained farmed mature Seriola fish, farmed fish of the genus Seriola that, after the maturation of the reproductive organs, have a degree of obesity of 17 or more and a body weight of 3.5 kg or more and a gonadal somatic index (GSI) lower than the values at the maturation of the reproductive organs.
<2> The method according to <1>, wherein the GSI of the cultured yellowtail fish after reproductive organ maturation is 2.5% or less for males and 1.0% or less for females.
<3> The method according to <1> or <2>, wherein the water temperature in the rearing environment of the Seriola spp. fish is adjusted to 15° C. to 28° C. from the start of rearing the Seriola spp. larvae.
<4> The method according to any one of <1> to <3>, further comprising removing individuals having morphological abnormalities and/or growth retardation during the rearing step and selecting individuals of fish of the genus Seriola.
<5> The method according to any one of <1> to <4>, wherein the rearing in the growing step includes marine aquaculture at a depth of 10 m to 18 m below the water surface for at least 5 months, and is carried out for 15 months or more.
<6> The method according to any one of <1> to <5>, wherein the fish of the genus Seriola are weighed and managed during the rearing.
<7> The method for rearing fish of the genus Seriola according to any one of <1> to <6>, comprising feeding the fish of the genus Seriola with a feed containing 0.1 to 0.3 parts by weight of chili pepper per 100 parts by weight of the feed for at least one month during the rearing.
<8> At the reproductive organ maturation stage, the obesity index is 18 or more, the body weight is 3.5 kg or more, and the gonadosomatic index (GSI) is 0.5% or more and 10.0% or less for males and 0.5% or more and 4.5% or less for females;
After reproductive organ maturation, the obesity index is 17 or more, the body weight is 3.5 kg or more, and the gonadosomatic index (GSI) is lower than the value at the reproductive organ maturation stage.
A farmed fish of the genus Yellowtail.
<9> The cultured fish of the genus Seriola according to <8>, wherein the GSI of the cultured fish of the genus Seriola after reproductive organ maturation is 2.5% or less for male individuals and 1.0% or less for female individuals.
<10> A farmed fish of the genus Yellowtail that is in the reproductive organ maturation stage, has a fatness index of 18 or more, a body weight of 3.5 kg or more, and a gonadosomatic index (GSI) of 0.5% to 10.0% in the case of males and 0.5% to 4.5% in the case of females.
<11> A farmed fish of the genus Yellowtail, which is an individual after maturation of reproductive organs, has a body mass index of 17 or more and a body weight of 3.5 kg or more, and has a gonadosomatic index (GSI) of less than 0.5% in the case of males and less than 0.5% in the case of females.
<12> The cultured yellowtail genus fish according to <8> or <10>, wherein the male yellowtail genus cultured fish at the stage of reproductive organ maturation satisfies at least one of the following (1) to (3):
(1) The blood concentration of 11-ketotestosterone (11-KT) is 1800 pg/mL to 4500 pg/mL,
(2) a blood concentration of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) of 100 pg/mL to 450 pg/mL, and
(3) Blood estradiol (E2) concentration is 130 pg/mL to 400 pg/mL.
<13> The cultured yellowtail fish according to <8> or <10>, wherein the female yellowtail fish at the stage of reproductive organ maturation satisfies at least one of the following (4) to (6):
(4) blood concentration of 11-ketotestosterone (11-KT) is 20 pg/mL to 175 pg/mL;
(5) 17α,20β-dihydroxy-4-pregnen-3-one (DHP) blood concentration is 100 pg/mL to 350 pg/mL, and
(6) Blood estradiol (E2) concentration: 300 pg/mL to 10,000 pg/mL.
<14> The cultured fish of the genus Yellowtail according to any one of <8> to <13>, having a fork length of 50 cm or more.
<15> The cultured fish of the genus Seriola according to any one of <8> to <14>, which is a yellowtail, a amberjack, an amberjack, or a long-finned amberjack.
<16> A cultured fish of the genus Seriola obtained by the method according to any one of <1> to <7>. <17> A method of raising Seriola fish in a regulated rearing environment for at least two months, and then starting rearing using Seriola fish larvae obtained by artificially collecting eggs, thereby growing Seriola fish;
Obtaining a mature cultured fish of the genus Yellowtail, which is a male individual having a gonadosomatic index (GSI) of 0.5% to 10.0% or a female individual having a GSI of 0.5% to 4.5% at the maturity stage of reproductive organs, and has a body fatness index of 18 or more and a body weight of 3.5 kg or more;
The present invention relates to a method for raising mature yellowtail farmed fish, the method including:

According to the present disclosure, it is possible to obtain farmed yellowtail fish that are less likely to lose weight after the maturation of their reproductive organs and have excellent sustainability.

A method for raising cultured fish of the genus Yellowtail according to one embodiment of the present disclosure includes raising Yellowtail fish in a regulated rearing environment for at least two months, then starting rearing using larvae of Yellowtail fish obtained by artificially collecting eggs to grow the Yellowtail fish, obtaining mature Yellowtail cultured fish that are males with a gonadosomatic index (GSI) of 0.5% to 10.0% or females with a GSI of 0.5% to 4.5% at the time of reproductive organ maturity, have a body mass index of 18 or more, and a body weight of 3.5 kg or more, and obtaining from the obtained mature Yellowtail cultured fish that, after the reproductive organ maturity stage, have a body mass index of 17 or more, a body weight of 3.5 kg or more, and a gonadosomatic index (GSI) lower than the values at the time of reproductive organ maturity.

Another aspect of the present disclosure provides cultured yellowtail fish obtained by the method for raising yellowtail fish according to the above aspect.
In another embodiment of the present disclosure, the farmed fish of the genus Yellowtail have, at the stage of reproductive organ maturation, a fatness index of 18 or more and a body weight of 3.5 kg or more, with a gonadal somatic index (GSI) of 0.5% or more and 10.0% or less in the case of males and 0.5% or more and 4.5% or less in the case of females, and after the stage of reproductive organ maturation, have a fatness index of 17 or more and a body weight of 3.5 kg or more, with a gonadal somatic index (GSI) lower than the values at the stage of reproductive organ maturation.

According to the method for raising farmed yellowtail fish in one aspect of the present disclosure, it is possible to obtain farmed yellowtail fish that are less likely to lose weight after the maturation of their reproductive organs and have excellent sustainability.

To explain this further, in the method of raising cultured yellowtail fish of the present disclosure, yellowtail fish are raised from yellowtail larvae obtained through artificial egg collection, and mature yellowtail cultured fish having a body weight of 3.5 kg or more, a body fatness index of 18 or more, and a predetermined GSI at the maturation of reproductive organs are obtained. From such mature yellowtail cultured fish having a body weight of 3.5 kg or more, a body fatness index of 18 or more, and a predetermined GSI, it is possible to obtain cultured yellowtail fish that maintain a body weight of 3.5 kg or more and a body fatness index of 17 or more, although the GSI decreases. Such cultured yellowtail fish having a body weight of 3.5 kg or more and a body fatness index of 17 or more have sufficient commercial value even after maturation of reproductive organs, and do not correspond to so-called "individuals that are thin after the maturation period."
Therefore, according to the disclosed method for raising farmed Yellowtail fish, it is possible to obtain farmed Yellowtail fish with a body weight of 3.5 kg or more and a fatness level of 17 or more that are not "individuals that are thin after the maturation period" even after the reproductive organs have matured.

In one embodiment of the present disclosure, a farmed fish of the genus Yellowtail has a body weight of 3.5 kg or more, an obesity index of 18 or more, and a GSI that is not too low at the reproductive organ maturation stage, even if the GSI after the reproductive organ maturation stage is lower than that at the reproductive organ maturation stage, and still has a body weight of 3.5 kg or more and an obesity index of 17 or more even after the reproductive organ maturation stage.
Therefore, it is possible to provide functional sperm or eggs at the reproductive organ maturity stage, and the sustainability of farming is excellent. After the reproductive organ maturity stage, the fish have a sufficiently high degree of obesity and weigh 3.5 kg or more, so that they have high nutritional value and a sufficiently high proportion of edible parts, which gives them high commercial value.

Another aspect of the present disclosure is a farmed fish of the genus Yellowtail that is an individual at the maturity stage of reproductive organs, has a body mass index of 18 or more and a body weight of 3.5 kg or more, and has a gonadal somatic index (GSI) of 0.5% or more and 10.0% or less in the case of males, and 0.5% or more and 4.5% or less in the case of females.
According to another aspect of the present disclosure, the reproductive organs of the cultured fish of the genus Yellowtail at maturity have a high degree of fatness and a sufficient body weight, and the GSI is not too low compared to that of wild yellowtail. This cultured fish of the genus Yellowtail at maturity can efficiently provide the cultured fish of the genus Yellowtail after reproductive organs have maturity according to the above aspect.

A method for raising reproductive-stage cultured fish of the genus Yellowtail according to another aspect of the present disclosure includes raising Yellowtail fish in a regulated rearing environment for at least two months, artificially collecting eggs to obtain Yellowtail larvae, initiating rearing of the obtained Yellowtail larvae and allowing them to grow into Yellowtail fish, and obtaining mature Yellowtail cultured fish that are male individuals with a GSI of 0.5% or more and 10.0% or female individuals with a GSI of 0.5% or more and 4.5% or less at the time of reproductive organ maturation, have a body fatness index of 18 or more, and a body weight of 3.5 kg or more.
According to the method for raising reproductive-stage cultured yellowtail fish of the present invention, it is possible to provide the above-mentioned useful cultured yellowtail fish in the reproductive organ maturity stage.

In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.
In this specification, any numerical range indicated using "to" indicates a range that includes the numerical values before and after as the minimum and maximum values, respectively.

In this specification, the amount of each component in a mixture means the total amount of the multiple substances present in the mixture when multiple substances corresponding to each component are present in the mixture, unless otherwise specified. In this specification, the content of each component in a mixture means the total content of the multiple substances present in the mixture when multiple substances corresponding to each component are present in the mixture, unless otherwise specified.
As used herein, the terms "less than" or "less than" in relation to percentages mean a range including 0%, i.e., "not containing," unless a lower limit is specifically stated, or including a value that is undetectable by current means.
The present disclosure will be described below.

In one embodiment of the present disclosure, at the stage of reproductive organ maturity, the cultured fish of the genus Yellowtail has a fatness index of 18 or more and a body weight of 3.5 kg or more, and a gonadal somatic index (GSI) of 0.5% or more in the case of males and 10.
In the case of males, the obesity index is 17 or more and the body weight is 3.5 kg or more after the maturation of the reproductive organs, and the gonadal somatic index (GSI) is lower than the values at the maturation of the reproductive organs.

The Seriola genus farmed fish includes Seriola dumerili, Seriola lalandi Valenciennes, Seriola quinqueradiata, Seriola rivoliana Valenciennes, Seriola carpenteri, Seriola fasciata, Seriola hippos Gunther, Seriola peruana Steindachner, and Seriola zonata. The low GSI Seriola genus farmed fish can be Seriola quinqueradiata, Seriola rivoliana Valenciennes, Seriola carpenteri, Seriola fasciata, Seriola hippos Gunther, Seriola peruana Steindachner, and Seriola zonata.

The cultured yellowtail fish may be cultured fish obtained by any method, and it is preferable that the fish be obtained by raising and managing them with a feed containing a compound feed.
"Formulated feed" means feed made up of a combination of ingredients that meets the protein, vitamins, minerals, and other nutrients required for the growth of fish. "Raising and managing" means that fish are raised using feed selected to achieve a specific purpose.

The body weight (total body weight) of the cultured fish of the genus Yellowtail according to the present disclosure is 3.5 kg or more both during and after the reproductive organ maturation stage. The body weight of the cultured fish of the genus Yellowtail during and after the reproductive organ maturation stage may be preferably 3.8 kg or more, more preferably 4.0 kg or more, even more preferably 4.2 kg or more, and even more preferably 4.5 kg or more. There may also be a change in body weight before and after the reproductive organ maturation stage of the cultured fish of the genus Yellowtail, and such a change in body weight may be an increase or decrease before and after the reproductive organ maturation stage. In the case of a decrease in body weight, the decrease in body weight may be, for example, within 0.5 kg, preferably within 0.3 kg, or within 0.2 kg.

In this specification, the term "reproductive organ maturation stage" refers to the stage in which the reproductive organs of fish of the genus Seriola generally acquire reproductive functions, and males are capable of spermatogenesis, while females are capable of spawning. In the case of Seriola, this generally corresponds to the stage when the fish are 26 to 27 months old after hatching, which usually corresponds to the period from April to May when the water temperature is 16°C to 19°C.
In this specification, "after the reproductive organ maturation stage" means a period after the reproductive organ maturation stage, i.e., after sperm release in the case of males, after spawning in the case of females, or after the weight of the reproductive organ reaches a maximum during the reproductive organ maturation stage and starts to decrease in the case of no sperm release or spawning. In the case of yellowtail, this generally corresponds to the age of 28 months or later, which usually corresponds to the period from May to September when the water temperature is 20°C or higher.
In this specification, the "stage of reproductive organ maturation" may be simply referred to as the "stage of maturation," and the "stage after the stage of reproductive organ maturation" may be simply referred to as "post-maturity."

In this specification, "male" refers to an individual that produces testes and has the chromosomal combination of ZZ type.In this specification, "female" refers to an individual that produces ovaries and has the chromosomal combination of ZW type or WW type.

The GSI of farmed yellowtail fish is 0.5% to 10.0% in the case of males and 0.5% to 4.5% in the case of females at maturity, and after maturity, the GSI becomes lower than that at maturity.
Hereinafter, farmed yellowtail fish weighing 3.5 kg or more and having a GSI of 0.5% to 10.0% in the case of males and 0.5% to 4.5% in the case of females at maturity may be referred to as "low GSI farmed yellowtail fish."
Gonad Somatic Index (GSI) as used herein is the ratio of gonad weight to fish body weight including internal organs, and is calculated based on the following formula:
GSI (%) = gonad weight (kg) / body weight including internal organs (kg) × 100

In the case of low GSI farmed yellowtail fish, the GSI at maturity is 0.5% or more, so it can be determined that the reproductive organs are sufficiently mature to produce functional sperm. On the other hand, since the GSI is 10.0% or less, it can be determined that the individual will not lose much weight due to the maturation of the reproductive organs after maturity.
The lower limit of the GSI in the mature stage may be 0.7% or more, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more, 4.0% or more, 5.0% or more, 6.0% or more, 7.0% or more, 7.2% or more, 7.5% or more, 7.7% or more, 8.0% or more, or 8.2% or more. The upper limit of the GSI in the mature stage may be 9.5% or less, 9.0% or less, or 8.8% or less.

When the low GSI farmed yellowtail fish is male, the reproductive organs include the testes. The weight of the reproductive organs, i.e., the testes, at maturity is generally 100g or more, and can be 120g or more, 150g or more, 180g or more, 200g or more, 250g or more, 300g or more, or 350g or more. There is no particular upper limit on the weight of the testes, but from the viewpoint of reducing the effect of leanness associated with maturation of the reproductive organs, it can be 450g or less, 430g or less, or 400g or less.

When low-GSI farmed yellowtail fish are female, the GSI at maturity is 0.5% or more, so it can be determined that the reproductive organs are sufficiently mature to produce functional eggs, while the GSI is 4.5% or less, so it can be determined that the individual is one that is less affected by the leanness that accompanies the maturation of the reproductive organs after maturity.
The lower limit of the GSI in the mature stage may be 0.7% or more, 1.0% or more, 1.5% or more, 2.0% or more, 2.5% or more, 3.0% or more, or 3.5% or more. The upper limit of the GSI in the mature stage may be 4.5% or less, 4.3% or less, 4.2% or less, or 4.0% or less.

When the low GSI farmed yellowtail fish is female, the reproductive organs include the ovaries. The weight of the reproductive organs, i.e., the ovaries, at maturity is generally 20g or more, and can be 30g or more, 40g or more, 50g or more, 80g or more, 100g or more, 120g or more, or 140g or more. There is no particular upper limit on the weight of the ovaries, but from the viewpoint of reducing the effect of leanness associated with maturation of the reproductive organs, it can be 300g or less, 250g or less, or 200g or less.

Because low-GSI farmed yellowtail fish have a GSI within a specified range as described above, the concentrations of various reproductive hormones at maturity can be made lower than those of wild yellowtail fish. Examples of reproductive hormones include 11-ketotestosterone (11-KT), 17α,20β-dihydroxy-4-pregnen-3-one (DHP), estradiol (E2), etc.

11-KT is one of the male hormones that functions as an endogenous androgen-like sex hormone, and is known to be involved in the middle stage of sperm maturation. In the case of males, the blood concentration of 11-KT in low GSI Seriola spp. farmed fish at the mature stage may be 1800 pg/mL or more, 2000 pg/mL or more, 2300 pg/mL or more, 2500 pg/mL or more, 2700 pg/mL or more, or 3000 pg/mL or more, or may be 4500 pg/mL or less, or 4300 pg/mL or less.

11-KT can also be produced in female individuals. The blood concentration of 11-KT in mature low GSI farmed Seriola spp. fish may be 20 pg/mL or more, 25 pg/mL or more, 30 pg/mL or more, 50 pg/mL or more, or 100 pg/mL or more, or may be 200 pg/mL or less, 180 pg/mL or less, or 160 pg/mL or less.

There is no particular limitation on the method for measuring 11-KT in blood, and any of the known measurement methods may be used. For example, time resolved fluoroimmunoassay (TIA) is used.
The measurement can be performed by TR-RIA. For example, the method described in Gen. Comp. Endocrinol. 106, 181-188 can be applied as the measurement method using TR-RIA.

DHP, also called 17α,20β-dihydroxy-4-pregnen-3-one, is a progestin that acts as an active form of testosterone, and is known as a hormone involved in the later stages of the maturation process of sperm or eggs.
The blood concentration of DHP in low GSI Seriola genus farmed fish at maturity may be 100 pg/mL or more, 110 pg/mL or more, 130 pg/mL or more, 150 pg/mL or more, or 200 pg/mL or more, and 450 pg/mL or less, 400 pg/mL or less, or 350 pg/mL or less, for male individuals. The blood concentration of DHP in low GSI Seriola genus farmed fish may be 100 pg/mL or more, 120 pg/mL or more, 150 pg/mL or more, or 200 pg/mL or more, and 350 pg/mL or less, 320 pg/mL or less, or 300 pg/mL or less, for female individuals.
There is no particular limitation on the method for measuring DHP in blood, and any of the known measurement methods may be used. For example, time resolved fluoroimmunoassay (TR)
The measurement method using TR-FIA can be, for example, the method described in Gen. Comp. Endocrinol. 106, 181-188.

E2 is one of the female hormones, also called 17-β-estradiol, and is known as a hormone that is directly or indirectly involved in the early stage of the maturation process of sperm or eggs via the liver. The blood concentration of E2 in low GSI Seriola genus farmed fish may be 130 pg/mL or more, 150 pg/mL or more, or 200 pg/mL or more, and may be 400 pg/mL or less, 380 pg/mL or less, or 350 pg/mL or less, in the case of male individuals. The blood concentration of E2 in low GSI Seriola genus farmed fish at the maturation stage may be 300 pg/mL or more, 500 pg/mL or more, 800 pg/mL or more, or 1000 pg/mL or more, and may be 15000 pg/mL or less, 10000 pg/mL or less, or 7000 pg/mL or less, in the case of female individuals.
There is no particular limitation on the method for measuring blood E2, and any known measurement method may be used. For example, it can be measured by radioimmunoassay (RIA). The measurement method using RIA is described, for example, in Cell Tissue Res., 218, 315-329.

The low GSI farmed Seriola spp. fish may have any of the above-mentioned reproductive hormones in the above-mentioned ranges. For example, mature low GSI farmed Seriola spp. fish may have the following combination of reproductive hormones:
If the farmed yellowtail fish is a male, at least one of the following (1) to (3):
(1) The blood concentration of 11-ketotestosterone (11-KT) is 1800 pg/mL to 4500 pg/mL,
(2) a blood concentration of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) of 100 pg/mL to 450 pg/mL, and
(3) Blood estradiol (E2) concentration is 130 pg/mL to 400 pg/mL.
If the farmed yellowtail fish is a female, at least one of the following (4) to (6):
(4) The blood concentration of 11-ketotestosterone (11-KT) is 20 pg/mL to 1
75 pg/mL,
(5) 17α,20β-dihydroxy-4-pregnen-3-one (DHP) blood concentration is 100 pg/mL to 350 pg/mL, and
(6) Blood estradiol (E2) concentration: 300 pg/mL to 10,000 pg/mL.

In the case of male individuals, at least one of the above (1) to (3) can be satisfied, for example, a combination of (1) and (2), a combination of (1) and (3), a combination of (2) and (3), or a combination of (1) to (3).
In the case of a female individual, at least one of the above (4) to (6) can be satisfied, for example, a combination of (4) and (5), a combination of (4) and (6), a combination of (5) and (6), or a combination of (4) to (6).

The GSI of low GSI farmed yellowtail fish is within a specified range at maturity and decreases after maturity. There are no particular restrictions on the extent of the decrease in GSI before and after maturity, so long as the body weight is maintained at 3.5 kg or more and the obesity index is maintained at 17 or more after maturity, and the GSI after maturity may be 95% or less, 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the GSI at maturity.

In low GSI farmed yellowtail fish, the GSI after maturation may be lower than the GSI value at maturity, i.e., less than the GSI value at maturity, for example, less than the GSI value at maturity, and may be 2.5% or less for males and 1.0% or less for females. In other words, farmed yellowtail fish after maturation may have a body fatness index of 17 or more and a body weight of 3.5 kg, and a GSI that is lower than the GSI at maturity, and may be 2.5% or less for males and 1.0% or less for females.
The GSI of a male individual after maturation may be less than the GSI value at maturity, and may be 2.5% or less, 2.0% or less, 1.8% or less, 1.5% or less, 1.3% or less, 1.0% or less, 0.8% or less, 0.5% or less, or 0.3% or less for males. The GSI of a female individual after maturation may be a lower GSI than the GSI at maturity, and may be 2.0% or less, 1.5% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, or 0.1% or less.

The obesity index of low GSI Seriola genus farmed fish at maturity is 18 or more, preferably 19 or more, more preferably 20 or more, and even more preferably 21 or more. There is no particular limit to the upper limit of the obesity index at maturity, so long as the obesity index after maturity is 17 or more, and it can be, for example, 30 or less, or 29 or less.
In addition, the obesity index of low-GSI Seriola genus farmed fish after maturation can be 17 or more, preferably 18 or more, and more preferably 19 or more. Low-GSI Seriola genus farmed fish having an obesity index of 17 or more after maturation can provide more edible parts with so-called fat compared to wild fish. There is no particular limit to the upper limit of the obesity index after maturation, and it can be, for example, 29 or less, or 28 or less.

The degree of obesity can generally be evaluated based on the following formula [1]:
Obesity level =
Weight (g)/{Fork length (cm) x Fork length (cm) x Fork length (cm)} x 1000... [1]

The low GSI cultured yellowtail fish of the present disclosure maintain a body weight of 3.5 kg or more during and after maturity, and even if the obesity level drops below that of the mature stage, the body weight remains at 17 kg or more after maturity.
The range of change in obesity index between maturity and post-maturity in low GSI Seriola genus farmed fish is not particularly limited as long as the obesity index is 17 or more after maturity, but is preferably within 2, more preferably within 1.

The fork length of low GSI farmed fish of the genus Seriola can be 50 cm or more, 55 cm or more, 57 cm or more, or 60 cm or more for both males and females. Low GSI farmed fish of the genus Seriola with a fork length of 50 cm or more tend to be more obese than wild fish, and can provide more edible portions. Fork length refers to the distance from the tip of the fish's head to the end of the center of the tail fin, and is an indicator of external morphology well known to those skilled in the art. Fork length is measured by measuring the linear distance in a plan view from the tip of the fish's head to the end of the center of the tail fin. There is no particular limit to the upper limit of the fork length of low GSI farmed fish of the genus Seriola, and it can be, for example, 200 cm or less.

To measure the weight of individual fish, first bleed the fish after landing and measure the weight of the remaining body, which is the "total fish weight." The internal organs are then removed and the weight of the gonads and liver can be measured separately. The weight can be measured using measuring devices normally used to measure the weight of fish and measuring devices normally used to measure the weight of internal organs.

In one embodiment of the present disclosure, the low GSI farmed yellowtail fish may have the following characteristics at the reproductive organ maturation stage:
(A1-1) A male individual having a body weight of 3.5 kg or more, an obesity index of 20 or more, and a GSI of 2.5% to 10.0%;
(A1-2) A male individual having a body weight of 4.0 kg or more, an obesity index of 20 or more, and a GSI of 5.0% to 9.0%;
(B1-1) A female individual having a body weight of 3.5 kg or more, an obesity index of 19 or more, and a GSI of 1.0% to 4.5%;
(B1-2) A female individual with a body weight of 4.0 kg or more, an obesity index of 19 or more, and a GSI of 2.0% to 4.0%.

In one embodiment of the present disclosure, the low GSI farmed fish of the genus Yellowtail may have the following characteristics: (A2-1) a male individual having a body weight of 3.5 kg or more and a body fatness index of 20 or more, a GSI of 2.5% to 10.0% at maturity, and a GSI of less than 2.5% after maturity; (A2-2) a male individual having a body weight of 4.0 kg or more and a body fatness index of 20 or more, a GSI of 5.0% to 9.0% at maturity, and a GSI of less than 5.0% after maturity;
(B2-1) A male individual having a body weight of 3.5 kg or more, an obesity index of 19 or more, a GSI of 1.0% to 4.5% at maturity, and a GSI of less than 1.0% after maturity;
(B2-2) A male individual having a body weight of 4.0 kg or more and an obesity index of 19 or more, a GSI of 2.0% to 4.0% at maturity, and a GSI of less than 2.0% after maturity.

The low GSI cultured fish of the genus Seriola according to the present disclosure has the body weight and fatness level as described above, and has a lower GSI than wild-caught yellowtail. Low GSI cultured fish of the genus Seriola with these characteristics can be at least 1.2 years old, or 1.5 years old or older, and generally 2 years old or 3 years old or older. In particular, the fish may be cultured not only in spring like wild yellowtail, but also in autumn. Cultured yellowtail with autumn eggs can be obtained by shifting the time of harvesting eggs or sperm from parent fish, for example by artificially controlling conditions such as light exposure and water temperature, or by administering maturation hormones.

Another cultured fish of the genus Yellowtail according to the present disclosure is a cultured fish of the genus Yellowtail that is in the reproductive organ maturation stage, has a body weight of 3.5 kg or more, a fatness index of 18 or more, and has a GSI of 0.5% to 20.0% in the case of males and 0.5% to 4.5% in the case of females. When specifically referring to such cultured fish of the genus Yellowtail, this specification may refer to it as a "mature low GSI cultured fish of the genus Yellowtail." The mature low GSI cultured fish of the genus Yellowtail may have the characteristics of (A1-1) to (A1-2) or (B1-1) to (B1-2) described above.
Mature low GSI cultured Seriola fish are preferred for efficiently obtaining mature low GSI cultured Seriola fish.

Other cultured fish of the genus Yellowtail disclosed herein are individuals after maturation of reproductive organs, have a body weight of 3.5 kg or more, a body fatness index of 17 or more, and a GSI lower than the GSI value at maturity. In this specification, such cultured fish of the genus Yellowtail may be referred to as "low GSI cultured fish of the genus Yellowtail after maturity." Examples of cultured fish of the genus Yellowtail after maturity with a body weight of 3.5 kg or more, a body fatness index of 17 or more, and a GSI of less than 2.5% for males and less than 1.0% for females may be cultured fish of the genus Yellowtail with a body weight of 3.5 kg or more, a body fatness index of 17 or more, and a GSI of less than 0.5% for males and less than 0.5% for females.

The matters regarding body weight, GSI, reproductive hormones, obesity level, fork length, etc. described above in relation to the low GSI cultured yellowtail fish of the present disclosure can be applied directly to mature low GSI cultured yellowtail fish and post-mature low GSI cultured yellowtail fish.

The low GSI cultured yellowtail fish according to the present disclosure can be obtained by controlling or adjusting the composition of the compound feed used in the culture, the day length conditions, the water temperature conditions, the culture period, the feeding amount, the body weight, etc., to adjust the GSI to a predetermined range. Examples of the method capable of adjusting the maturation of the gonads include the methods described in JP 2013-188207 A, JP 2013-188207 A, and JP 2015-510878 A. Among them, the application of a method of adjusting the maturation of the gonads based on the composition of the compound feed capable of adjusting the maturation of the gonads, the day length conditions and the water temperature conditions capable of adjusting the maturation of the gonads, is preferable in terms of the introduction of less foreign substances.
The cultured fish of the genus Yellowtail according to the present disclosure can be obtained by the method for raising cultured fish of the genus Yellowtail described in this specification.

<How to raise farmed yellowtail fish>
The breeding method for low-GSI cultured fish of the genus Yellowtail according to the present disclosure includes: breeding Yellowtail fish in a regulated breeding environment for at least two months, then starting breeding using larvae of Yellowtail fish obtained by artificially collecting eggs to grow the Yellowtail fish (hereinafter sometimes referred to as the "breeding process"); obtaining mature Yellowtail cultured fish that are male individuals with a GSI of 0.5% or more and 10.0% or female individuals with a GSI of 0.5% or more and 4.5% or less at the time of reproductive organ maturation, have a body mass index of 18 or more and a body weight of 3.5 kg or more (hereinafter sometimes referred to as the "mature individual obtaining process"); and obtaining from the obtained mature Yellowtail cultured fish, after reproductive organ maturation, cultured Yellowtail fish that have a body mass index of 17 or more and a body weight of 3.5 kg or more and have a GSI lower than the numerical value at the time of reproductive organ maturation (hereinafter sometimes referred to as the "post-maturity individual obtaining process"), and may include other processes as necessary.
According to the present rearing method for rearing cultured yellowtail fish, it is possible to obtain cultured yellowtail fish that are less likely to lose weight after the maturation of their reproductive organs and that have excellent sustainability.
In addition, the "breeding method" can be considered as a method for producing the low GSI Seriola aquacultured fish of the present disclosure, and can be used interchangeably with any of the terms "production method,""productionmethod," etc.
Furthermore, "controlled rearing" refers to rearing while appropriately adjusting the photoperiod and water temperature conditions.

[Breeding process]
In the rearing step, Seriola species are reared for at least two months in a regulated rearing environment, and then eggs are artificially harvested to obtain larvae of Seriola species.
The larvae may be obtained by purchase or other means from Seriola spp. larvae obtained by artificially harvesting eggs from Seriola spp. that have been reared in a regulated rearing environment for two months, or the larvae may be obtained by a person carrying out the rearing process by carrying out at least one of the following means: rearing in the regulated rearing environment for at least two months, and harvesting the eggs.
In addition, the collected eggs are subjected to a fertilization treatment after collection in order to obtain larvae. The fertilization treatment may be performed by the person performing the rearing process, or the person performing the rearing process may obtain the larvae obtained after the fertilization treatment by means of purchase or the like and use them for rearing in the rearing process.
The photoperiod conditions in regulated rearing refer to an appropriate combination of a 9-15 hour light period and a 9-15 hour dark period. For example, short-day conditions may be a 10 hour light period and a 14 hour dark period for 30 days, while long-day conditions may be a 14 hour light period and a 10 hour dark period for 60 days. The water temperature conditions refer to adjusting the water temperature within the range of 15°C to 30°C or 16°C to 28°C.
The photoperiod and water temperature conditions in the regulated rearing can be appropriately adjusted according to the rearing. For example, if a preferable light-dark cycle or water temperature can be achieved in a natural environment, the conditions can be applied as they are.

Rearing in a regulated rearing environment can be carried out for at least two months, preferably three months or more, and more preferably seven months or more. By adjusting the photoperiod and water temperature conditions, for example, it is possible to promote the maturation of the reproductive organs of female individuals, which makes it possible to collect eggs at least three months earlier than in wild yellowtail.

Eggs are collected artificially. Here, "artificially" means that spawning is induced under an externally controlled environment, such as by adjusting the environment or administering drugs. As a result, eggs can be collected earlier than in wild yellowtail, for example. In Japan, eggs can be collected at any time of the year.
The collected eggs are then subjected to a fertilization treatment. After fertilization, the fertilized eggs are kept under a specific environment to obtain larvae of the Seriola spp. The larvae of Seriola spp. are then subjected to growth.

In the rearing step, rearing is started using larvae of fish of the genus Seriola to grow the fish of the genus Seriola. In order to start rearing larvae of fish of the genus Seriola and grow the fish of the genus Seriola, the fish may be reared in an environment suitable for the growth stage from larvae to adults using a method normally used. Once Seriola fish have reached a size suitable for marine culture, they may be reared on the sea surface. Rearing of fish of the genus Seriola may be carried out in an environment in which Seriola typically grows.
In this specification, "larvae of fish of the genus Seriola" refers to individuals whose fork length is less than about 5 cm after hatching, and subsequent juvenile fish and adult fish are collectively referred to as "fish of the genus Seriola".

From the viewpoint of growth efficiency of Seriola fish, the water temperature in the rearing environment is preferably adjusted to 15° C. to 28° C. In this case, by adjusting the water temperature in the rearing environment to within the range of 15° C. to 28° C. from the start of rearing Seriola fish larvae, the growth rate of Seriola fish can be increased from the early stage of the rearing stage, compared to starting at a later stage, and low-GSI cultured Seriola fish can be obtained efficiently.
The adjustment of the water temperature in the rearing process can be changed depending on the rearing stage. For example, for rearing larvae of Seriola spp., the temperature can be adjusted to 18° C. to 22° C., and after the larvae have grown into Seriola spp., the temperature can be adjusted to 15° C. to 28° C. Examples of adjustment of the water temperature include adding water, heating, adjusting the ambient temperature, shading, adjusting the hours of sunlight, selecting a sea surface farm, transferring the reared fish to a tank, etc.
The rearing process may include a period of high water temperature exceeding 28°C. For example, exposing maturing Seriola spp. fish to high water temperatures of 30°C or higher may be effective in adjusting maturation by imposing moderate stress on the individual. The water temperature that constitutes the "high water temperature" in the rearing process may be, for example, 29°C, 30°C, or 31°C. The period of high water temperature may be 1 day or more, 2 days or more, 3 days or more, or 5 days or more. The period of high water temperature may be a continuous period or may be intermittent.

In order to more effectively obtain the desired cultured yellowtail fish, the rearing step may include removing individuals with morphological abnormalities and/or poor growth during the rearing step and selecting individuals of yellowtail fish. Morphological abnormalities and/or poor growth can be determined based on feeding efficiency, feeding rate, body weight, body length, fork length, etc. Body weight, body length, fork length, etc. may be collectively referred to simply as "size" in this specification. Examples of morphological abnormalities include depressed head, curvature of the spine, short body, jaw abnormalities, etc. The selection rate due to morphological abnormalities or poor growth can be evaluated by the following formula.
Selection rate (%) = number of normal fish / (number of morphologically abnormal or growth-stunted fish + number of normal fish) x 100

In the rearing process, weighing management of the individual fish can be performed. Weighing management of the individual fish can be performed in combination with individual selection based on morphological abnormalities and/or poor growth. Weighing management means periodically measuring or estimating the size of the farmed yellowtail fish and managing it. There are no particular limitations on the method of weighing management, and examples include weight measurement and image analysis. For example, the weight of the individual fish can be measured every month. In this case, the weight of each individual fish, i.e., the body weight, can be measured, or several dozen fish can be measured together, the average can be calculated, and the average value can be used for management. In addition, for example, "AM-100" (AQ1 systems) can be used as the image analysis means. For example, "AM-100" (AQ1 systems) can be used as the weight measurement means.

The rearing period for the yellowtail fish in the rearing process can be continued until mature individuals weighing 3.5 kg or more are obtained, and can be 12 months or more, 15 months or more, 18 months or more, 20 months or more, or 22 months or more. The rearing process can be continued until the post-mature individual acquisition process described below.

The rearing process may be carried out in the ocean or on land. From the viewpoint of ease of individual management and the efficiency of obtaining low GSI Seriola aquaculture fish, it is preferable to include marine aquaculture at 10 to 18 meters below the water surface for at least 5 months. This type of marine aquaculture is also called the submerged type, and is easy to provide a rearing environment with excellent water temperature stability and less susceptible to the effects of waves, etc. Marine aquaculture can be carried out for at least 5 months, at least 6 months, or at least 8 months. There is no particular limit to the upper limit of the period of marine aquaculture, and it can be set appropriately depending on the rearing period.

In the area 10 to 18 m below the surface where marine culture is carried out, the water temperature is often constant in the range of 15°C to 28°C, which is preferable from the viewpoint of environmental stability. However, the position below the surface where marine culture is carried out may be shallower than 10 m or deeper than 18 m. When feeding, the position of marine culture can be raised from the sea to the sea surface. In addition, the shallower the position, the higher the water temperature, and the deeper the position, the lower the water temperature. By utilizing this, the water temperature can be adjusted depending on the position where marine culture is carried out. In addition, the above-mentioned high water temperature breeding may be applied when carrying out marine culture. In this case, for example, by moving the breeding position closer to the sea surface where the water temperature is more likely to be high, a breeding environment with a high water temperature can be easily provided, and maturation adjustment can be performed more efficiently.
In this disclosure, when the upper limit of the cage used for aquaculture is located above sea level, it is referred to as marine aquaculture, and when the upper limit of the cage is located below sea level, it is referred to as submarine aquaculture.

There are no particular limitations on the feed used in the rearing process, and any feed normally used for cultured yellowtail fish can be used without limitation. As feed for yellowtail fish, a feed containing 0.1 to 0.3 parts by weight of chili pepper per 100 parts by weight of feed can be used. Hereinafter, this feed is referred to as "chili pepper-containing feed". Chili pepper is known to have an effect of improving or maintaining the color tone of dark muscle in cultured yellowtail fish (for example, JP 2009-232864 A), and is also effective in obtaining low GSI yellowtail fish. The chili pepper in the chili pepper-containing feed can be chili pepper components or chili pepper powder.

The chili-containing feed may contain clove oil in addition to chili peppers. The amount of clove oil to be added may be 0.1 to 0.25 parts by weight per 100 parts by weight of the feed.
There is no particular limitation on the period of feeding with the chili pepper-containing feed, and the feeding can be carried out for, for example, at least one month, at least two months, or at least three months.

In order to efficiently obtain low GSI cultured yellowtail fish, it is preferable to feed the yellowtail fish without any restrictions during the breeding period in the breeding process. In other words, in the breeding process, it is preferable to feed the yellowtail fish satiationally without any restrictions on the amount and composition of the feed. Satiation feeding means feeding until no individuals are observed on the water surface that require food. In order to more efficiently obtain low GSI cultured yellowtail fish, it is preferable to feed the yellowtail fish satiationally. Satiation feeding means feeding until no feeding is observed while observing with an underwater camera. This allows for satiation of more individuals, preferably all individuals under breeding, by taking into account underwater feeding behavior that cannot be confirmed on the water surface. By feeding the yellowtail fish satiationally, the growth rate of the yellowtail fish in the breeding process is fast, and mature low GSI cultured yellowtail fish can be obtained more reliably.

In the rearing process, it is preferable to remove individuals with at least one type of growth deficiency selected from the group consisting of morphological abnormalities and growth deficiency. By removing individuals with such growth deficiencies, it is possible to select individuals with a better growth state than the growth state of the gonads, and more efficiently obtain low GSI cultured yellowtail fish. Individuals with morphological abnormalities are individuals with depressed heads, curvature of the spine, short bodies, jaw abnormalities, etc., and individuals that can be clearly confirmed to have external abnormalities through observation. Individuals with growth deficiencies are individuals that can be clearly confirmed to be inferior to the growth state of the same period through observation. Individuals with morphological abnormalities are prone to growth deficiencies in terms of total body weight, since their growth is restricted. If morphological abnormalities do not stop the growth of the gonads, individuals with high GSI growth deficiencies can be eliminated by removing individuals with morphological abnormalities.

[Mature individual acquisition process]
In the process of obtaining mature individuals, mature cultured yellowtail fish are obtained which are male individuals with a GSI of 0.5% or more and 10.0% or female individuals with a GSI of 0.5% or more and 4.5% or less at the maturity stage of reproductive organs, and have a fatness index of 18 or more and a body weight of 3.5 kg or more.
The mature Yellowtail cultured fish obtained here are mature individuals having a body weight of 3.5 kg or more and a fatness index of 18 or more, and have a lower GSI than wild or other farmed fish at the mature stage. By obtaining such mature Yellowtail cultured fish, it is possible to obtain post-maturity low-GSI Yellowtail cultured fish in the subsequent post-maturity individual acquisition step.
In the step of obtaining mature individuals, individuals having the desired GSI, body weight and obesity degree can be selected by measuring the size, blood hormone concentration, etc. The method already described for the weighing management can be applied to measure the size. Examples of blood hormones include 11-KT, DHP, E2, etc. The above-mentioned method can be applied to measure 11-KT, DHP and E2.

The obesity index of mature cultured yellowtail fish is relatively high, and may be preferably 19 or more, 20 or more, or 21 or more. There is no particular upper limit to the obesity index of mature cultured yellowtail fish, and it may be, for example, 28 or less, or 27 or less. The above-mentioned points can be directly applied to mature cultured yellowtail fish.
Mature cultured yellowtail fish can be obtained by the rearing method including the mature individual acquisition step. Since the reproductive organs of the mature cultured yellowtail fish obtained here are sufficiently mature, eggs or sperm can be obtained from these individuals. The eggs or sperm from the mature cultured yellowtail fish obtained here can be used as seed for obtaining cultured yellowtail larvae having useful characteristics. In other words, the rearing method for cultured yellowtail fish according to the present disclosure can be said to be excellent in the sustainability of the culture. Furthermore, the mature cultured yellowtail fish may be supplied to the next post-mature individual acquisition step.

[Post-maturity individual acquisition process]
In the post-maturity individual acquisition step, from the obtained mature Yellowtail cultured fish, there are obtained Yellowtail cultured fish having a body fatness index of 17 or more, a body weight of 3.5 kg or more, and a GSI lower than that at the maturity stage of reproductive organs, i.e., post-maturity Yellowtail cultured fish. For the post-maturity Yellowtail cultured fish, the matters described above regarding the post-maturity low GSI Yellowtail cultured fish can be directly applied.
The obtained post-maturity cultured yellowtail fish are cultured yellowtail fish that have been prevented from losing weight to less than 3.5 kg or a fatness index of less than 17, and such useful traits can be passed on to the next generation.
Individuals having the desired GSI, body weight and obesity level can be selected based on values such as size and blood hormone concentrations, as in the case of mature cultured Yellowtail fish, or can be selected by landing the fish and measuring the weight of their reproductive organs.

[Application]
Furthermore, by using the method for raising cultured yellowtail fish according to the present disclosure, it is possible to adjust the timing of providing cultured yellowtail fish having good characteristics. The post-maturity cultured yellowtail fish according to the present disclosure can be provided at an appropriate time depending on the condition of the cultured fish, for example, within six months, four months, three months, or two months from maturity. For example, when three-year-old mature yellowtail cultured fish are obtained from April to May, the post-maturity cultured yellowtail fish can be provided from May to September. This makes it possible to stably provide cultured yellowtail fish that show good fatness and body weight before the summer when red tides are likely to occur.

The low GSI farmed fish of the genus Seriola according to the present disclosure has sufficient body weight and fatness, and therefore has high nutritional value as a farmed fish. Therefore, compared with wild-caught Seriola, and furthermore, compared with farmed fish of the genus Seriola that have a fatness level of less than 17 and a high GSI, the low GSI farmed fish of the genus Seriola according to the present disclosure can have a high proportion of high-quality edible parts.
The edible parts of farmed yellowtail fish are preferably used as processed foods, such as the following heated and unheated foods, and can also be used as animal feed. The processed foods and animal feed according to one embodiment can include the edible parts of low GSI yellowtail fish.

Examples of animal feed include cat food, dog food, farmed fish feed, poultry feed, and livestock feed. There is no particular restriction on the proportion of the edible portion of the low GSI farmed yellowtail fish in the animal feed, and it can be 0.1% to 100% by weight, for example. In addition to the edible portion of the low GSI farmed yellowtail fish, the animal feed can contain other nutrients such as vitamins, carriers acceptable for animal feed such as water, and other additives such as excipients, as necessary, depending on the type of target animal. The animal feed may be contained in a container as described below. Examples of food include non-heated food and heated food.

One embodiment of the present disclosure includes a processed food product of low GSI farmed fish of the genus Seriola, comprising an edible portion of the low GSI farmed fish of the genus Seriola and a container for containing the edible portion. The processed food product may include a heated product and an unheated product.
Non-heated products refer to edible parts that have not been cooked with heat, and examples of such products include minced meat, sashimi, fillets, blocks, and fillets, as well as frozen, chilled, freeze-dried, dried, and pickled products. The fact that a product has not been cooked with heat can be determined by the color tone of the surface of the edible part. In this specification, "heating" means that heat is applied to a state in which actomyosin is denatured to a degree that can be visually recognized. When the edible parts of farmed fish are subjected to heat treatment, the edible parts change color due to the denaturation of actomyosin, so it can be determined based on the discoloration of the edible parts.
The term "heated food" refers to edible parts that have been cooked by heating, and examples of such foods include boiled foods, baked foods, steamed foods, fried foods, and paste products.

There are no particular limitations on the shape of the edible part contained in the processed food, and the edible part may have a shape specific to the part, may be an irregular shape obtained by shredding, or may be molded into a specific shape.

The processed food may contain at least one selected from the group consisting of other foods, food ingredients, and accessories, as necessary. Examples of other foods include rice, pickles (Japanese radish, seaweed, etc.), ginger, sprouts, etc. Examples of food ingredients include green onions for negitoro. Examples of accessories include, for example, balances, labels, ice packs, cooling agents, ice, dry ice, sherbet ice, etc. The accessories may be contained in the container together with the edible portion, or may be placed on the outside of the container, and may be integral with the container or may be attached so as to be freely detachable. Each of the other foods, food ingredients, and accessories may be a combination of one or more.

The container may be any material that can be used to contain the edible portion, such as polystyrene foam, paper, vinyl, soft plastic, hard plastic, metal, or glass. The shape of the container may be any material that can contain the edible portion, such as packaging sheets, trays with or without lids, bags, cans, or bottles.

The low GSI farmed yellowtail fish of the present disclosure can be crossed with other low GSI farmed yellowtail fish or farmed yellowtail fish with other traits. This allows for the production of offspring with the genetic traits of the low GSI farmed yellowtail fish to be used as seed for farming.

The present disclosure will be described in detail below with reference to examples. However, the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" are based on mass.

[Example 1]
Yellowtail larvae were reared in a natural environment for 24 months, and then rearing was started from the 29th month by adjusting the photoperiod and water temperature. Feeding was normally once a day, and once every two days in winter. Photoperiod conditions were short and long. Other rearing conditions were adjusted according to the conditions described in JP 2007-300837 A.

Spawning was induced by injection of a hormone agent, and eggs were collected from female individuals. Sperm was collected from male individuals and fertilized to obtain yellowtail larvae. The larvae were reared on land at a water temperature of 18°C to 20°C. From the third month after they had grown into fry, they were reared in a fish cage installed on the sea surface. The fry were lowered 10m to 18m below the water surface to begin underwater culture. The water temperature was adjusted to 15°C to 22°C during the fry stage. The water temperature was adjusted to 15°C to 28°C during the adult stage, and during the rearing period, the water temperature was adjusted to at least 30°C for two or more consecutive days during the period when the weight of the growing individuals reached about 500g to 1kg, allowing the growing individuals to experience high water temperatures.

Feeding was performed once a day in normal conditions, once every two days in winter, and throughout the year, with no feeding restrictions. However, this feeding was not based on the usual method of feeding by observing the surface of the water, but on the optimal feeding method obtained by observing feeding behavior underwater with a camera. During the marine culture period, the juvenile or adult fish were raised submerged 10 to 18 m below the water surface, and were pulled up to the sea surface each time they were fed. The feed used was a commercially available EP (extruded pellet) with 0.1 to 0.3 parts by weight of chili powder added to 100 parts by weight of the feed.
When the fry reached 2g to 20g, they were removed from the land tank and moved to a sea pen. This operation is also called "release into the ocean." After the release into the ocean during the rearing period, the body length, size, morphology, etc. were checked at any time, and the weight was measured every month. For the weight measurement, a weight measurement method using an AM-100 (AQ1 system) was adopted. Based on these results, only individuals without morphological abnormalities (depressed head, curvature of the spine, short body, jaw abnormality) and with a good growth rate were bred. The selection rate for morphological abnormalities, etc. was 50 to 95%.

At the stage of reproductive organ maturity, which is more than five months after the start of marine culture, two-year-old male fish were obtained with an average weight of 4.63 kg, an average fork length of 61.03 cm, and an average obesity index of 20.35, and two-year-old female fish with an average weight of 4.66 kg, an average fork length of 61.60 cm, and an average obesity index of 19.91. The gonad weights of these two-year-old fish were measured to calculate the GSI, and the blood hormone concentrations were measured as follows.

Blood was drawn from the heart of the fish, centrifuged, and the supernatant was collected and stored at −80° C. until analysis. When drawing blood, a syringe treated with heparin sodium (concentration: 5,000 units/mL, Wako Pure Chemical Industries, Ltd.) was used.
The amount of 11-KT was measured using Testosterone, 11-Keto-, EIA Kit (Strip Plate) (Cayman Chemicals). The amount of DHP was measured by time resolved fluoroimmunoassay (TR-FIA) using Maturation-Inducing Steroid (salmonid) AChE Tracer, Maturation-Inducing Steroid (salmonid) EIA Antiserum, and Precoated (Mouse Anti-Rabbit IgG) EIA 96well Strip Plate according to the method described in Gen. Comp. Endocrinol. 106, 181-188. The amount of E2 was measured using Estradiol, EIA Kit (Strip Plate) (Cayman Chemicals).
The results are shown in Table 1.

As shown in Table 1, we were able to obtain farmed mature yellowtail fish with a body weight of 3.5 kg or more and a fatness index of 18 or more, despite their low GSI.

These mature cultured yellowtail fish were able to spawn or release sperm. When the cultured yellowtail fish obtained were crossed with individuals with low GSI, yellowtail larvae of the next generation could be obtained. In other words, the cultured yellowtail fish obtained in this example can be said to have excellent sustainability in aquaculture.
The mature farmed yellowtail fish obtained were confirmed to have a body weight of 3.5 kg or more and a fatness index of 17 or more in June, two months after maturity, and a GSI of less than 0.5 for both males and females.

[Example 2]
In the same manner as in Example 1, larvae obtained by early egg collection were reared to obtain two-year-old female mature cultured yellowtail fish and April female post-maturity cultured yellowtail fish, 74 days after maturity. The body weight, body fatness and GSI of these mature cultured yellowtail fish and post-maturity cultured yellowtail fish were measured in the same manner as in Example 1. The results are shown in Table 2.
As shown in Table 2, even after maturity, the individuals had body weights of 3.5 kg or more and obesity levels of 17 or more.

This farmed yellowtail fish has a sufficiently low GSI, so the edible portion is high, and it also has a high degree of fatness, making it highly valuable commercially, and it is delicious to eat.

In this way, according to the present disclosure, it is possible to obtain farmed yellowtail fish that are less likely to lose weight after the maturation of their reproductive organs and have excellent sustainability.

Claims (4)

A female farmed yellowtail fish,
At the stage of reproductive organ maturity, the body mass index is 18 or more, the fork length is 50 cm, and the gonadosomatic index (GSI) is 0.5% or more and 4.5% or less;
After reproductive organ maturation, the body mass index is 17 or more and the fork length is 50 cm or more, and the gonadosomatic index (GSI) is lower than the value at the time of reproductive organ maturation.
Yellowtail farmed fish. 2. The cultured yellowtail fish according to claim 1 , wherein the GSI of the cultured yellowtail fish after reproductive organ maturation is 1.0% or less in female individuals. A farmed yellowtail fish that is a female individual after the reproductive organs have matured, has a body mass index of 17 or more, a fork length of 50 cm or more, and a gonadal somatic index (GSI) of less than 0.5%. The cultured yellowtail fish according to claim 1 , wherein the female yellowtail fish at the stage of reproductive organ maturation satisfies at least one of the following (4) to (6):
(4) blood concentration of 11-ketotestosterone (11-KT) is 20 pg/mL to 175 pg/mL;
(5) 17α,20β-dihydroxy-4-pregnen-3-one (DHP) blood concentration is 100 pg/mL to 350 pg/mL, and
(6) Blood estradiol (E2) concentration: 300 pg/mL to 10,000 pg/mL.