Methods for raising farmed yellowtail fish

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 fish of the genus Yellowtail. [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 such as selecting and growing only the larger juvenile fish (mojako) that are collected, or cultivating artificial seedlings by collecting eggs from parent fish and hatching them, are being used.

[0003] Patent Document 1 describes a method for shortening the rearing period for yellowtail, in which male and female artificially reared yellowtail broodstock are placed in land-based tanks in early September, and after controlling the photoperiod and water temperature to enlarge their ovaries, eggs are harvested in December using an early egg collection technique in which hormones are injected to induce spawning, and some of the resulting larvae are cultured for one year and the resulting adult fish are shipped, while the remaining larvae are raised as broodstock for two years and then the above-mentioned early egg collection technique is used to harvest eggs in December, repeating this process, thereby shortening both the yellowtail farming period and the broodstock rearing period by approximately one year. It is known that the rearing period for farmed yellowtail fish can be shortened by using so-called artificial seedlings, in which the fish are placed in an artificial environment from the hatching stage, and by managing and controlling the rearing environment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-300837 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a rearing method that enables early rearing of cultured yellowtail fish, in addition to or instead of the conventional methods of selecting young fish or using artificial seedlings. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have discovered that early rearing of hatched farmed yellowtail fish, separated by sex, accelerates the growth of both sexes, and have thus completed the present invention. [1] A method for raising cultured yellowtail fish, comprising the step of raising yellowtail fish in a cage containing only female yellowtail fish or in a cage containing only male yellowtail fish for a raising period of at least two months. [2] The method described in [1], which includes a step of sorting farmed yellowtail fish that are 24 months or less after hatching into a cage containing only female yellowtail farmed fish or a cage containing only male yellowtail farmed fish, prior to the rearing step. [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] Mature farmed yellowtail 14 to 20 months after hatching, with 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. [Effects of the Invention]

[0007] According to the present invention, it is possible to quickly raise cultured yellowtail fish in addition to or instead of the conventional selection of fry or the use of artificial seedlings. Furthermore, the present invention makes it possible to provide cultured yellowtail fish that have a higher body weight than conventional fish during the raising period after hatching. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a graph showing the changes in average fish weight of farmed yellowtail in each area. [Figure 2] This is a graph showing the average fish weight of farmed yellowtail in each area as of late May. [Figure 3] This is a 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 graph shows 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. [Figure 5] These are histologically stained images of the ovaries of female yellowtail from each group at maturity. A is a histologically stained image of the ovaries of a yellowtail from the female group, and B is a histologically stained image of the ovaries of a yellowtail from the mixed group. The scale bar in the image represents 200 μm. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1.Definition As used herein, the term "genus Seriola" refers to fish classified in the family Carangidae of the order Perciformes, and is known by the scientific name Seriola. Fish of the genus Seriola include yellowtail (Seriola quinqueradiata), amberjack (Seriola dumerili), yellowtail (Seriola lalandi), long-finned amberjack (Seriola rivoliana), Seriola carpenteri, Seriola fasciata, Seriola hippos, Seriola peruana, Seriola quinqueradiata, and Seriola zonata. In particular, yellowtail or amberjack is included. In particular, yellowtail is included.

[0010] As used herein, "farmed fish" refers to fish that have been fed and raised under controlled conditions in fish pens or other containers before shipping, regardless of the length of the period. As used herein, "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 conditions after being caught at sea until shipping. "Under controlled conditions" as used here refers to an environment in which various conditions are artificially controlled. Specific conditions are described in Section "2. Raising methods 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 using the following formula: GSI=gonad weight (g) / body weight (g)×100 The gonad weight here refers to the weight of the ovaries in females and the testes in males. In this specification, the "maturity period" refers to the period of the year when GSI is highest in conventionally farmed 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 depression in the center where the tail fin forks.

[0013] 2. Cultivation method for farmed yellowtail fish A first embodiment of the present invention is a method for raising cultured yellowtail fish, characterized by including a step of raising yellowtail fish in a cage containing only female yellowtail fish or in a cage containing only male yellowtail fish for a raising 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. The reason for this is not clear, but it is thought that when male and female yellowtail fish are raised in the same pen, the presence of the opposite sex stimulates them to mature faster, and nutrients are used more for the formation of the gonads 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 wild-caught fry (natural seedlings) or may be eggs collected from parent fish and 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 seedling fry.

[0016] The cultured fish of the genus Seriola 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 in mixed pens.

[0017] It is preferable to separate and raise farmed fish by sex at an early stage after hatching. The method of this embodiment preferably includes a step of sorting farmed Seriola spp. 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 separate the fish by sex before hatching.

[0018] The means for separating hatched farmed fish into males and females are not particularly limited, and any of the following methods can be used: separation by observing the shape of the fish's gonads, detection of genetic sex identification markers, and breeding. Observing the shape of the fish's gonads involves inserting a cannula into the gonads through the cloaca to observe the gonads. While this is a relatively simple method, it requires the fish's gonads to mature to a certain extent, so it is only applicable to farmed fish that are at least eight months old after hatching. Known sex identification markers for farmed yellowtail fish include those described in JP 2014-180233 A. Detection of sex identification markers enables the separation of males and females of farmed fish soon after hatching, but requires tedious work, such as collecting samples from the caudal fin, blood, etc. from each individual, extracting DNA, and conducting genetic analysis.

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

[0020] The rearing period for sexed farmed yellowtail fish is 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. Preferably, the rearing period is 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 cages or tanks during the above-mentioned rearing period is preferably 13 to 28° C., particularly 18 to 27° C., and even more preferably 20 to 25° C. Because cages for farmed yellowtail fish are usually installed on the sea, it is difficult to artificially adjust the water temperature in the cages after installation. However, by appropriately selecting the installation location of the cages, it is possible to carry out farming under desired temperature conditions.

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

[0023] During the above-mentioned rearing period, feeding is preferably carried out by scattering food in the cage at least once every two days. Regarding the feed used, any feed known to be suitable for fry of farmed yellowtail fish can be used before they reach adulthood. For example, live feed such as small sardines, granular or pelleted compound feed, moist pellets, etc. can be used. During the rearing period after they reach adulthood, any feed known to be suitable for farmed yellowtail fish can be used, for example, live feed such as mackerel or sardines, or compound feed such as pellets. The period until farmed yellowtail fish reach adulthood 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 raised by the method of this embodiment is not particularly limited as long as it belongs to the genus Seriola, but may be, for example, yellowtail or amberjack. In particular, yellowtail may be used. In one aspect of the method of this embodiment, the start of the rearing period for male and female yellowtail can be set to 12 months or less after hatching. In this case, it is possible to raise mature yellowtail 14 to 20 months after hatching that meet the following criteria: Fish weight: 2.4 kg or more, preferably 2.5 kg or more, 2.6 kg or more, 2.7 kg or more, 2.8 kg or more, 2.9 kg or more, or 3.0 kg 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 sex-separated rearing period for obtaining farmed yellowtail 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. The earlier the sex separation is performed, the longer the rearing period can be.

[0026] 3. Farmed Yellowtail The second embodiment of the present invention is cultured yellowtail. The cultured yellowtail of this embodiment is cultured yellowtail at maturity, 14 to 20 months after hatching, characterized by a fish 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. More specifically, the cultured yellowtail of this embodiment is cultured yellowtail raised using one aspect of the method of the first embodiment.

[0027] The farmed yellowtail of this embodiment satisfies the following criteria. Fish weight: 2.4 kg or more, preferably 2.5 kg or more, 2.6 kg or more, 2.7 kg or more, 2.8 kg or more, 2.9 kg or more, or 3.0 kg 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 in separate sexes tend to have larger fish body weights and smaller GSIs than those reared in mixed sexes. [Example]

[0029] Example 1: Survey of the growth status of sex-segregated yellowtail aquaculture (1) Raising artificial Mojako On January 18, first-generation artificially hatched yellowtail (12 females and 8 males) were artificially inseminated to obtain fertilized eggs. After confirming hatching on January 20, the fish were placed in land-based tanks for rearing. From February 28 to March 5, they were released into the ocean and continued rearing in the fish pens. On June 9, the fish were measured. The average fish weight was 74.4 g. On July 11, they were vaccinated and measured. The average fish weight was 176.7 g. Each fish was then 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-sex groups (mixed group) and placed in separate pens for further rearing. The pens for each group were spaced at least 30 m apart. The distance between each cage was set so that the yellowtail raised 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 approximately three times the length and width of the cage, but this is not limited to this. The size of each cage was 4m long x 4m wide x 4m deep, and from the 15th month of sea surface rearing onwards, it was set to 8m long x 8m wide x 8m deep. The water temperature in the cages was 15.2-31.0°C. Formulated feed was used.

[0030] (2) Rearing and fish weight measurement After measuring the fish body weight on July 11th, the yellowtail in each cage were reared for approximately 10 months until May of the following year, during which time fish weight was measured 10 times at regular intervals of approximately one month. Figure 1 shows the change in average fish weight in each area. Fish weight was measured by randomly sampling 50 fish from each test area. Figure 2 shows the fish weight in each area as of late May. Fish weight was high in all cages reared separately for males and females, with the female area showing particularly high fish weight. On the other hand, fish weight in the mixed area was lower than in the female and male areas, and no difference between males and females was 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 their fork length, body weight, GSI, and blood sex hormones were measured. The gonads of each fish were also collected, stained with hematoxylin and eosin, and examined under a microscope. Blood samples were collected from each fish and estradiol (E2) levels were measured for females and 11-ketotestosterone (11-KT) levels for males by ELISA using commercially available assay kits. The 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 time course of GSI in the female, male, and mixed groups. Figure 3A shows the GSI for females, and Figure 3B shows the GSI for males. An asterisk (*) in the figure indicates a significant difference (P<0.05) determined by the Mann-Whitney U test. Figure 4 shows the blood sex hormone concentrations in each group. Figure 4A shows the blood E2 concentration for females, and Figure 4B shows the blood 11-KT concentration for males. An asterisk (*) in the figure indicates a significant difference (P<0.05) determined by the Mann-Whitney U test. At maturity (April and May), the GSI in the female group was significantly lower than that of females in the mixed group. The GSI values ​​for males were also lower in both the male and mixed groups. Before maturity, blood E2 concentrations in females were comparable in the female and mixed groups, but by April, when they reached their peak maturity, only the female group showed a significant decrease. The concentration of 11-KT in the blood of males was equal in both the male and mixed groups before maturity, but was lower in the male group at the time of maximum maturity in April. The above results indicate that rearing males and females separately results in a lower maturity of each individual than rearing males and females together.

[0037] Figure 5 shows histologically stained photographs of ovaries from the female and mixed groups taken in early April. Figure 5A is an example of a micrograph showing the condition of the ovaries of a yellowtail individual from the female group, and Figure 5B is an example of a micrograph showing the condition of the ovaries of a yellowtail individual from the mixed group. The scale bar in the figure represents 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 at the maturation stage in April than in the mixed group.

Claims

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

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

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 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. A farmed female yellowtail at maturity 14 to 20 months after hatching, with a body weight of 2.4 kg or more, a gonadosomatic index (GSI) of less than 0.4, and a blood estradiol concentration of 150 pg / mL or less.

8. The farmed yellowtail described in claim 7, which is a female farmed yellowtail in early April.

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