Rearing method of cultured fish of genus seriola

Abstract

To provide a rearing method that enables early growth of cultured fish of the genus Seriola.SOLUTION: Cultured fish of genus Seriola within 24 months after being incubated is distributed into a crawl including only female cultured fish of genus Seriola or a crawl including only male cultured fish of genus Seriola, and rearing of the fish is performed for at least two months in the crawl including only female cultured fish of genus Seriola or a crawl including only male cultured fish of genus Seriola.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for raising fast-growing cultured yellowtail fish. [Background technology]

[0002] Attempts are being made to shorten the growing period for farmed fish in order to reduce farming costs, etc. In the case of yellowtail farming, in order to ship earlier than usual, especially in the summer when supply is low, methods that have been adopted include, for example, selecting and growing only the larger juvenile fish (mojako) that have been caught, and cultivating artificial seedlings by collecting eggs from parent fish and hatching them.

[0003] As a method for shortening the rearing period of yellowtail, Patent Document 1 describes a method in which male and female artificially reared parent fish of yellowtail are housed in land-based tanks in early September, their ovaries are enlarged by controlling the day length and water temperature, and then eggs are harvested in December using an early egg collection technique in which a hormone is injected to induce spawning, some of the larvae are cultured for one year, and the resulting adult fish are shipped, while the remaining larvae are raised as parent fish for two years, and the above-mentioned early egg collection technique is used to harvest eggs in December. This method shortens the rearing period of yellowtail and parent fish rearing period by about one year each. It is known that the rearing period of farmed yellowtail fish can be shortened by adopting so-called artificial seedlings, which are placed in an artificial environment from the hatching stage, and managing and controlling the rearing environment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-300837 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a breeding method that enables early breeding of cultured yellowtail fish in addition to, or instead of, the conventional selection of juvenile fish or the use of artificial seedlings. [Means for solving the problem]

[0006] As a result of intensive research, the present inventors have discovered that by separately raising male and female cultured yellowtail fish at an early stage after hatching, the growth of both males and females can be accelerated, and have thus completed the present invention. [1] A method for raising cultured fish of the genus Seriola, comprising a step of raising cultured fish of the genus Seriola in a net cage containing only female cultured fish of the genus Seriola or in a net cage containing only male cultured fish of the genus Seriola for a raising period of at least two months. [2] The method according to [1], further comprising a step of sorting, prior to the rearing step, cultured Seriola spp. that are 24 months or less after hatching, into a cage containing only female Seriola spp. cultured fish or a cage containing only male Seriola spp. cultured fish. [3] The method according to [1] or [2], which includes artificially hatching eggs collected from parent fish and cultivating the resulting fry. [4] The method according to any one of [1] to [3], wherein the cultured yellowtail fish is female. [5] The method according to any one of [1] to [4], wherein the farmed fish of the genus Yellowtail is farmed Yellowtail. [6] The method according to [5], wherein the start of the rearing period is 12 months or less after hatching, the rearing period is 2 to 20 months, the body weight of the resulting farmed yellowtail at maturity 14 to 20 months after hatching is 2.4 kg or more, and the gonadosomatic index (GSI) is less than 1.0 for males and less than 0.4 for females. [7] Farmed yellowtail at maturity, 14 to 20 months after hatching, weighing 2.4 kg or more, and having a gonadosomatic index (GSI) of less than 1.0 for males and less than 0.4 for females. Effect of the Invention

[0007] According to the present invention, it is possible to rapidly grow cultured yellowtail fish in combination with or instead of the selection of juvenile fish or the use of artificial seedlings, which have been conventionally carried out. Furthermore, the present invention makes it possible to provide cultured yellowtail fish that have a higher body weight than conventional fish during the growth period after hatching. [Brief description of the drawings]

[0008] [Figure 1] 1 is a graph showing changes in average fish weight of farmed yellowtail in each area. [Diagram 2] This is a graph showing the average fish weight of farmed yellowtail in each area as of late May. [Diagram 3] Graph showing the change in GSI of farmed yellowtail in each group. A shows the change in GSI of female farmed yellowtail in each group. B shows the change in GSI of male farmed yellowtail in each group. [Figure 4] This is a graph showing the blood sex hormone concentrations of farmed yellowtail in each group. A shows the estradiol (E2) concentration in each female group. B shows the 11-ketotestosterone (11-KT) concentration in each male group. [Diagram 5] These are histological staining images of female ovaries from each group at maturity. A is a histological staining image of the ovaries of yellowtail from the female group, and B is a histological staining image of the ovaries of yellowtail from the mixed group. The scale bar in the figure indicates 200 μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] 1.Definition In this specification, the term "genus Seriola" refers to fish classified in the family Carangidae of the order Perciformes, and known by the scientific name Seriola. Fish of the genus Seriola include Seriola quinqueradiata, Seriola dumerili, Seriola lalandi, Seriola rivoliana, Seriola carpenteri, Seriola fasciata, Seriola hippos, Seriola peruana, Seriola quinqueradiata, and Seriola zonata. In particular, Seriola quinqueradiata and Seriola zonata are included. In particular, Seriola quinqueradiata and Seriola zonata are included.

[0010] In this specification, "farmed fish" refers to fish that have been fed and raised under controlled breeding conditions in a fish pen or the like before shipping, regardless of the length of time. In this specification, "farmed fish" includes both natural seedlings and artificially hatched seedlings. In contrast, "wild fish" refers to fish that have not been fed or raised under controlled breeding conditions after being caught at sea until shipping. "Under controlled breeding conditions" here refers to an environment in which various conditions are artificially controlled. Specific conditions are described in Section "2. Raising method for farmed yellowtail fish."

[0011] As used herein, the term "gonad somatic index (GSI)" refers to the proportion of gonads to the body weight of an individual, and is calculated by the following formula: GSI=gonad weight (g) / body weight (g)×100 The gonad weight here refers to the weight of the ovaries in the case of females and the testes in the case of males. In this specification, the "maturity stage" refers to the period in which the GSI is highest in a conventional cultured yellowtail fish, more specifically, the period from April to May.

[0012] In this specification, "fork length" refers to the length from the tip of the upper jaw to the outer edge of the central depression where the tail fin forks.

[0013] 2. Cultivation method of yellowtail fish A first embodiment of the present invention is a method for growing cultured Seriola spp. The method of this embodiment is characterized by including a step of growing Seriola spp. in a cage containing only female Seriola spp. or in a cage containing only male Seriola spp. for a growing period of at least two months.

[0014] When farmed yellowtail fish are raised in separate pens for males and females, their growth rate increases significantly and their maturity decreases compared to when they are raised together. Although the reason for this is not clear, it is presumed that when farmed yellowtail fish of the genus are raised in the same pen, the presence of the opposite sex stimulates them to mature faster, and nutrients are used preferentially for the formation of the gonads rather than for the growth of the fish itself, whereas when they are raised separately for males and females, more nutrients are used for the growth of the fish itself.

[0015] The cultured yellowtail fish raised by the method of this embodiment may be either wild fry caught and raised (natural seedlings), or eggs collected from parent fish that have been artificially hatched (artificial seedlings). When natural seedlings are used, unlike artificial seedlings, the period after hatching cannot be accurately determined in days, but can be estimated in months from the spawning period of normal wild yellowtail fish. In the method of this embodiment, it is preferable to raise artificial fry.

[0016] The cultured fish of the genus Seriola to be raised by the method of this embodiment are preferably female. The present inventors have found that when cultured fish of the genus Seriola are raised in separate fish pens for males and females, and particularly when only females are raised, the fish weight increases significantly compared to when males and females are raised together.

[0017] It is preferable that farmed fish are separated into males and females at an early stage after hatching. The method of this embodiment preferably includes a step of dividing farmed Seriola spp. fish that are 24 months or less after hatching, particularly 12 months or less, 10 months or less, 9 months or less, 8 months or less, 7 months or less, 6 months or less, 5 months or less, 4 months or less, 3 months or less, 2 months or less, or 1 month or less after hatching, into a cage containing only female Seriola spp. farmed fish or a cage containing only male Seriola spp. farmed fish. Alternatively, it is preferable to divide the fish into males and females before hatching.

[0018] The means for separating the hatched cultured fish into males and females is not particularly limited, and any of the following methods can be used: separation by observing the shape of the gonads of the fish, detection of genetic sex identification markers, and breeding. Observation of the shape of the gonads of the fish is a method of observing the gonads by inserting a cannula into the gonads from the cloaca. Although this is a relatively simple method, it requires the gonads of the fish to mature to a certain extent, so it can only be applied to cultured fish that have been hatched for about 8 months or more. As a sex identification marker for cultured yellowtail fish, for example, the marker described in JP 2014-180233 A is known. Detection of the sex identification marker makes it possible to separate the males and females of cultured fish soon after hatching, but it requires complicated work such as taking samples of the tail fin, blood, etc. from each individual, extracting DNA, and conducting genetic analysis.

[0019] The male and female cultured yellowtail fish are raised in separate land tanks or marine cages. When the fish are raised in cages, the cages are not adjacent to each other, and are preferably spaced at least 5 m apart, and more preferably 10 m apart. The distance between the cages for the male and female cultured yellowtail fish is not particularly limited, but it is desirable that the cages are spaced apart enough that the male and female yellowtail fish cannot recognize each other.

[0020] The rearing period for the male and female cultured yellowtail fish can be 2 months or more, preferably 3 months or more, 4 months or more, 5 months or more, 6 months or more, 7 months or more, 8 months or more, 9 months or more, 10 months or more, 11 months or more, 12 months or more, 18 months or more, 19 months or more, 20 months or more, 21 months or more, 22 months or more, 23 months or more, 2 years or more, or 3 years or more. Also, preferably, the rearing period can be 6 years or less, 5 years or less, 4 years or less, 3 years or less, 2 years or less, 23 months or less, 22 months or less, 21 months or less, or 20 months or less.

[0021] The water temperature in the cage or tank during the above-mentioned growing period is preferably 13 to 28° C., particularly 18 to 27° C., and further preferably 20 to 25° C. Since cages for farmed yellowtail are usually installed on the sea, it is difficult to artificially adjust the water temperature in the cage after installation. However, for example, by appropriately selecting the installation location of the cage, it is possible to carry out farming under desired temperature conditions.

[0022] The stocking density of cultured yellowtail in the cages is 3 to 20 kg / m 3 , especially 7-16kg / m 3 The size of the cage or tank is not particularly limited as long as each individual can swim without coming into contact with other individuals, but may be, for example, about 8 to 60 m in length and width and 8 to 25 m in depth.

[0023] The feeding during the above-mentioned rearing period is preferably carried out by scattering the food in the cage at least once every two days. The food used before the fish become adults can be any food known as a food suitable for juveniles of cultured fish of the genus Seriola. For example, live food such as small sardines, granular or pelleted compound feed, moist pellets, etc. can be used. During the rearing period after the fish become adults, any food known as a food for cultured fish of the genus Seriola, for example, live food such as mackerel or sardines or compound feed such as pellets, etc. can be used. The period until cultured fish of the genus Seriola become adults varies greatly depending on the fish species and rearing conditions, but in the case of artificial seedlings, it is usually 14 to 36 months after hatching.

[0024] The type of cultured fish of the genus Seriola to be cultivated by the method of this embodiment is not particularly limited as long as it is a fish belonging to the genus Seriola, but may be, for example, a yellowtail or an amberjack. In particular, it may be a yellowtail. In one aspect of the method of this embodiment, the start time of the cultivation period for male and female yellowtails may be 12 months or less after hatching. In this case, it is possible to cultivate cultured yellowtails that are in the mature stage 14 to 20 months after hatching and that satisfy the following indicators. Fish weight: 2.4kg or more, preferably 2.5kg or more, 2.6kg or more, 2.7kg or more, 2.8kg or more, 2.9kg or more or 3.0kg or more. Gonadal Somatic Index (GSI): for males, less than 1.0, preferably less than 0.95, less than 0.90, less than 0.85 or less than 0.8, for females, less than 0.4, preferably less than 0.39, less than 0.38, less than 0.37, less than 0.36, less than 0.35, less than 0.34, less than 0.33, less than 0.32, less than 0.31 or less than 0.30.

[0025] The period for raising males and females separately to obtain farmed yellowtails 14 to 20 months after hatching varies depending on the time of sex separation, but is at least 2 months and at most 20 months. By separating the males and females earlier, it is possible to extend the period.

[0026] 3. Farmed Yellowtail The second embodiment of the present invention is a cultured yellowtail. The cultured yellowtail of this embodiment is a mature cultured yellowtail 14 to 20 months after hatching, characterized in that the fish weight is 2.4 kg or more and the gonadosomatic index (GSI) is less than 1.0 for males and less than 0.4 for females. More specifically, the cultured yellowtail of this embodiment is a cultured yellowtail raised by one aspect of the method of the first embodiment.

[0027] The cultured yellowtail of this embodiment satisfies the following criteria. Fish weight: 2.4kg or more, preferably 2.5kg or more, 2.6kg or more, 2.7kg or more, 2.8kg or more, 2.9kg or more or 3.0kg or more. Gonadal Somatic Index (GSI): for males, less than 1.0, preferably less than 0.95, less than 0.90, less than 0.85 or less than 0.8, for females, less than 0.4, preferably less than 0.39, less than 0.38, less than 0.37, less than 0.36, less than 0.35, less than 0.34, less than 0.33, less than 0.32, less than 0.31 or less than 0.30.

[0028] The cultured yellowtail of this embodiment is preferably female. Compared to males, females reared separately from males tend to have larger fish weights and smaller GSIs than those reared together. EXAMPLES

[0029] Example 1: Survey of growth status of yellowtails cultured separately for male and female (1) Cultivation of artificial Mojako On January 18, 12 females and 8 males of the first generation of artificially hatched yellowtails were artificially fertilized to obtain fertilized eggs. After confirming hatching on January 20, they were kept in an onshore tank for rearing, and then released into the sea from February 28 to March 5 to continue rearing in the fish cages. On June 9, the fish were measured. The average fish weight at this time was 74.4g. On July 11, the fish were vaccinated and measured. The average fish weight at this time was 176.7g. After that, each fish was tagged for individual identification and sexed. On August 9, the fish were divided into 250 males (male group), 250 females (female group), and 259 mixed sexes (mixed group) and placed in separate cages for further rearing. The cages for each group were placed at least 30m apart. The distance between each cage was set so that the yellowtails reared in each cage could not recognize each other directly by sight or indirectly by secreting sex hormones. For example, the separation distance was set to about three times the length and width of the cage, but is not limited to this. The size of each cage was 4m long x 4m wide x 4m deep, and after the 15th month of sea surface rearing, it was set to 8m long x 8m wide x 8m deep. The water temperature in the cage was 15.2 to 31.0°C. Formulated feed was used as feed.

[0030] (2) Rearing and weight measurement of fish After the fish body measurements on July 11th, the yellowtail in each net cage were grown for approximately 10 months until May of the following year, during which time fish weights were measured 10 times at regular intervals of about one month. Figure 1 shows the change in average fish weight in each area. Fish weights were measured by randomly sampling 50 fish from each test area. Figure 2 shows the fish weights in each area as of late May. Fish weights were high in all net cages grown separately for males and females, with the female area showing particularly high fish weights. On the other hand, fish weights in the mixed area were lower than those in the female and male areas, with no difference between males and females being observed.

[0031] (3) Gonad observation In early March, early April, late April, and late May, 4-10 male and female fish were sampled from each area, and fork length, fish weight, GSI, and blood sex hormones were measured. In addition, the gonads of each fish were collected, stained with hematoxylin-eosin staining solution, and observed under a microscope. For sex hormone measurements, blood was collected from each fish, and estradiol (E2) was measured for females and 11-ketotestosterone (11-KT) for males by ELISA using a commercially available measurement kit. The measurement results for each area are shown in Tables 1-4.

[0032] [Table 1]

[0033] [Table 2]

[0034] [Table 3]

[0035] [Table 4]

[0036] Figure 3 shows the change in GSI over time in the female, male and mixed groups. Figure 3A shows the GSI in females, and Figure 3B shows the GSI in males. The "*" in the figure indicates that there was a significant difference (P<0.05) by the Mann-Whitney U test. Figure 4 shows the blood sex hormone concentrations in each group. Figure 4A shows the blood E2 concentration in females, and Figure 4B shows the blood 11-KT concentration in males. The "*" in the figure indicates that there was a significant difference (P<0.05) by the Mann-Whitney U test. It was shown that the GSI in the female group was significantly lower than that of females in the mixed group during the maturation period (April and May). The GSI of males was also lower in both male groups compared to the mixed group. Before maturation, the blood E2 concentration in females was the same in the female and mixed groups, but it was shown that only the female group showed a large decrease at the time of maximum maturity in April. The concentration of 11-KT in the male blood was the same in both the male and mixed groups before maturity, but was lower in the male group at the time of maximum maturity in April. This shows that rearing males and females separately results in a lower maturity of each individual than rearing them together.

[0037] Figure 5 shows histologically stained photographs of the ovaries of the female and mixed groups in early April. Figure 5A is an example of a micrograph showing the condition of the ovaries of individual yellowtail in the female group, and Figure 5B is an example of a micrograph showing the condition of the ovaries of individual yellowtail in the mixed group. The scale bar in the figure indicates 200 μm. As shown in Figure 5B, vitellogenic oocytes were observed in individuals with high E2 concentrations in the mixed group. In contrast, as shown in Figure 5A, no vitellogenic oocytes were observed in the female group. This indicates that the ovarian maturity was lower in the female group in April, which is the maturation period, compared to the mixed group.

Claims

1. A method for raising cultured fish of the genus Seriola, comprising a step of raising cultured fish of the genus Seriola in a cage containing only female cultured fish of the genus Seriola or in a cage containing only male cultured fish of the genus Seriola for a raising period of at least two months.

2. The method according to claim 1, further comprising a step of sorting, prior to the rearing step, cultured Seriola spp. that are 24 months or less after hatching, into a cage containing only female Seriola spp. cultured fish or a cage containing only male Seriola spp. cultured fish.

3. The method according to claim 1, comprising artificially hatching eggs collected from parent fish and cultivating the resulting fry.

4. The method according to claim 1 , wherein the farmed yellowtail fish is female.

5. The method according to claim 1 , wherein the farmed fish of the genus Seriola is farmed Seriola.

6. The method according to claim 5, wherein the start of the rearing period is 12 months or less after hatching, the rearing period is 2 to 20 months, the body weight of the obtained cultured yellowtail at maturity 14 to 20 months after hatching is 2.4 kg or more, and the gonadosomatic index (GSI) is less than 1.0 for males and less than 0.4 for females.

7. A farmed yellowtail at a mature stage 14 to 20 months after hatching, the fish having a body weight of 2.4 kg or more and a gonadosomatic index (GSI) of less than 1.0 for males and less than 0.4 for females.

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