JP7728307B2 - Methods for raising farmed yellowtail fish - Google Patents

Description

The present invention relates to a method for raising fast-growing farmed yellowtail fish.

Attempts are being made to shorten the growing period for farmed fish, with the aim of reducing farming costs, etc. In the case of yellowtail farming, in order to ship them earlier than usual, especially during 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.

Patent Document 1 describes a method for shortening the yellowtail rearing period, 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. Some of the resulting larvae are then cultured for one year, after which the resulting adult fish are shipped. The remaining larvae are then cultured as broodstock for two years, and the above-mentioned early egg collection technique is used to harvest eggs in December. This method is repeated, shortening both the yellowtail rearing period and the broodstock rearing period by approximately one year. In this way, it is known that the rearing period for farmed yellowtail fish can be shortened by using so-called artificial seedlings, which are placed in an artificial environment from the hatching stage, and managing and controlling the rearing environment.

Japanese Patent Application Laid-Open No. 2007-300837

The present invention aims to provide a breeding method that enables the rapid rearing of farmed yellowtail fish, in addition to or instead of the conventional methods of selecting young fish or using artificial seedlings.

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 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.
[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 comprises 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.

The present invention makes it possible to rapidly raise farmed yellowtail fish in combination with, or instead of, the conventional methods of selecting young fish or using artificial seedlings. Furthermore, the present invention makes it possible to provide farmed yellowtail fish that have a heavier body weight than conventional fish during the post-hatching rearing period.

1 is a graph showing the changes in average fish weight of farmed yellowtail in each area. 1 is a graph showing the average fish weight of farmed yellowtail in each area as of late May. 1 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. 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. 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 indicates 200 μm.

1. Definitions In this specification, 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 amberjack (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.

In this specification, "farmed fish" refers to fish that have been fed and raised under controlled conditions in fish pens or other facilities 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 conditions after being caught at sea until shipping. "Under controlled conditions" 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."

As used herein, the term "gonad somatic index (GSI)" refers to the proportion of gonads in an individual's body weight, and is calculated using the following formula:
GSI = gonad weight (g) / body weight (g) x 100
The gonad weight here refers to the weight of the ovaries in females and the weight of the testes in males. As used herein, the term "maturity period" refers to the period of the year when the GSI is highest in conventionally farmed yellowtail fish, more specifically, the period from April to May.

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.

2. Method for Raising Cultured Yellowtail Fish The first embodiment of the present invention is a method for raising cultured Yellowtail fish. The method of this embodiment is characterized by including a step of raising cultured 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.

Raising farmed yellowtail fish in separate pens for males and females significantly increases their growth rate and reduces their maturity compared to when they are raised together. The underlying mechanism is not fully understood, 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 more quickly, and nutrients are used more for gonad formation than for fish growth, whereas when they are raised separately for males and females, more nutrients are used for fish growth.

The cultured yellowtail fish raised using the method of this embodiment may be wild-caught fry (natural seedlings), or may be obtained by artificially hatching eggs collected from parent fish (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 based on the spawning period of normal wild yellowtail fish. In the method of this embodiment, it is preferable to raise artificial seedling fry.

The cultured fish of the genus Yellowtail raised using the method of this embodiment are preferably female. The inventors have found that when cultured fish of the genus Yellowtail are raised in separate pens for males and females, and particularly when only females are raised, the fish's body weight increases significantly compared to when they are raised in a mixed-sex pen.

It is preferable to separate 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 pen containing only female Seriola spp. farmed fish or a pen containing only male Seriola spp. farmed fish. Alternatively, it is preferable to separate the fish by sex before they hatch.

The means for separating farmed fish into males and females after hatching are not particularly limited, but 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 makes it possible to separate farmed fish into males and females soon after hatching, but requires tedious work, such as collecting samples from the tail fin and blood of each individual, extracting DNA, and conducting genetic analysis.

Sexed farmed yellowtail fish are raised in separate terrestrial tanks or marine cages. When raised in cages, the cages are not adjacent to each other, but are preferably spaced at least 5 m apart, and more preferably 10 m apart. There are no particular restrictions on the distance between cages for sexed farmed yellowtail fish, but it is desirable that the cages be spaced far enough apart that the male and female fish cannot distinguish from each other.

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. 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.

During the above-mentioned rearing period, the water temperature in the cages or tanks should preferably be 13-28°C, particularly 18-27°C, and even more preferably 20-25°C. Because cages for farmed yellowtail are usually installed at sea, it is difficult to artificially adjust the water temperature inside the cages after installation. However, by appropriately selecting the location of the cages, it is possible to cultivate the fish under the desired temperature conditions.

The rearing density of farmed yellowtail fish in the cage is preferably 3 to 20 kg/m ³ , and particularly 7 to 16 kg/m ^3. The size of the cage or tank is not particularly limited as long as each fish can swim without coming into contact with other fish, but can be, for example, approximately 8 to 60 m in length and width and 8 to 25 m in depth.

During the above-mentioned rearing period, feeding is preferably carried out by scattering food inside the cage at least once every two days. Before the fish reach adulthood, any known feed suitable for juvenile farmed yellowtail fish can be used. For example, live bait such as small sardines, granular or pelleted compound feed, or moist pellets can be used. During the rearing period after the fish reach adulthood, any known feed suitable for farmed yellowtail fish can be used, for example, live bait 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 artificially reared fish, it usually takes 14 to 36 months after hatching.

The type of cultured fish of the genus Seriola that can be raised by the method of this embodiment is not particularly limited as long as it belongs to the genus Seriola, but can be, for example, Japanese amberjack or amberjack. In particular, Japanese amberjack can 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.

The sex-separated rearing period required to obtain farmed yellowtail, which is 14 to 20 months after hatching, varies depending on when the sexes are separated, but is at least two months and at most 20 months. The earlier the sexes are separated, the longer the rearing period can be.

3. Cultured 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 in that the fish weighs 2.4 kg or more and has 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.

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.

The farmed 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 1: Growth Status Investigation of Yellowtail Cultured by Gender (1) Raising Artificial Mojako On January 18, 12 female and 8 male first-generation artificially hatched yellowtail were artificially mated to obtain fertilized eggs. After confirming hatching on January 20, the fish were housed in land-based tanks for rearing, and then released into the ocean from February 28 to March 5 for continued rearing in fish pens. On June 9, fish were measured. The average fish weight at this time was 74.4 g. On July 11, vaccinations and fish measurements were performed. The average fish weight at this time was 176.7 g. Subsequently, each individual 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-sex group (mixed group) and placed in separate fish pens for continued rearing. The cages in each section were spaced at least 30 m apart. The distance between the cages 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 4 m long x 4 m wide x 4 m deep, and from the 15th month of sea surface rearing onwards, it was set to 8 m long x 8 m wide x 8 m deep. The water temperature in the cages was 15.2 to 31.0°C. Formulated feed was used.

(2) Rearing and fish weight measurement After measuring the fish body weight on July 11, 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.

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

Figure 3 shows the changes in GSI over time 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 the male group compared to the mixed group. Before maturity, blood E2 concentrations in females were comparable in the female and mixed groups, but by April, when they reach their peak of maturity, only the female group showed a significant decrease. Prior to maturity, the concentrations of 11-KT in the male blood were equal in the male and mixed groups, but by April, when they reach maximum maturity, the concentrations were lower in the male group. This shows that rearing males and females separately results in a lower maturity level for each individual compared to rearing males and females together.

Figure 5 shows histologically stained photographs of ovaries from the female and mixed groups 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 image 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 level of ovarian maturity was lower in the female group at the maturation stage in April compared to the mixed group.

Claims (8)

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. The method of claim 1, further comprising, prior to the rearing step, a step of sorting farmed Seriola spp. that are 24 months or less after hatching into a pen containing only female Seriola spp. farmed fish or a pen containing only male Seriola spp. farmed fish. The method of claim 1, which comprises artificially hatching eggs collected from parent fish and cultivating the resulting fry. The method of claim 1, wherein the farmed yellowtail fish is female. The method of claim 1, wherein the farmed fish of the genus Yellowtail is farmed Yellowtail. 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. 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 . The cultured yellowtail according to claim 7, which is a female cultured yellowtail in early April .