Whiteleg shrimp

Abstract

To provide a crustacean from which hatched larvae can be stably obtained.SOLUTION: Provided is a whiteleg shrimp obtained by rearing one or more individual whiteleg shrimp that have reached a body weight at which spawning is possible at a rearing temperature of 21°C to 23°C for a cumulative period of 90 days or more. Also provided is a whiteleg shrimp obtained by rearing one or more individual whiteleg shrimp that have reached a body weight at which spawning is possible in a first period in which an average temperature T1 is 19°C or less, and thereafter rearing the shrimp in a second period in which an average temperature T2 is 27°C or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for regulating maturation of crustacean ovaries, a method for producing crustacean hatchlings, a method for producing crustaceans, and crustaceans. [Background technology]

[0002] In crustacean breeding, methods for controlling the maturation of female ovaries have been investigated to adjust the production of hatched larvae, which serve as seedlings. When ovarian maturation begins, the oviduct begins to elongate, and as maturation progresses, the ovaries develop significantly. Ovarian maturation is divided into four stages, I, II, III, and IV, based on the degree of ovarian development, with stages I and II sometimes being evaluated as immature, and stages III and IV as mature. Females whose ovaries have fully matured release their eggs into an aquarium. Once the female releases her eggs, the ovarian maturation stage returns to stage I. Crustaceans then cycle through the cycle of immature, mature, and spawning in the same way. Non-Patent Document 1 describes the effect of removing the eyestalks of vannamei shrimp on their reproductive ability. Non-Patent Document 2 describes the effect of feeding lugworms to wild-caught kuruma shrimp and rearing them at low water temperatures on their spawning. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Zakea Sultana et al., "Reproductive performance of Litopenaeus vannamei reared on different diets under experimental conditions and the effect of eyestalk ablation on it," Nippon Suisan Gakkaishi, 89(2), p127-136, February 2023 [Non-patent document 2] Yasuyuki Uto et al., "Selection of parent shrimp candidates from wild kuruma shrimp and control of spawning by low water temperature treatment of mature shrimp," Chiba Prefectural Fisheries Research Center, Chiba Prefectural Fisheries Research Center Research Report, No. 6, pp. 17-23, March 2011 Summary of the Invention [Problem to be solved by the invention]

[0004] In the production of Crustacean seedlings, it is necessary to consistently secure hatched larvae, which are the seedlings. When a female Crustacean reaches a weight sufficient for egg-laying, her ovaries mature, and shedding occurs. After egg-laying, the female's ovaries mature again and shedding occurs again. Thus, female Crustaceans undergo ovarian maturation and egg-laying repeatedly throughout their lives, allowing for repeated production of hatched larvae from a single individual. However, repeated egg-laying by a female can reduce the hatching rate and decrease the efficiency of obtaining hatched larvae. Furthermore, because the time from egg-laying to the next ovarian maturation varies among individuals, the timing of ovarian maturation and egg-laying varies among individuals, making it difficult to consistently obtain hatched larvae. Therefore, the present disclosure provides a method for adjusting the maturation of Crustacean ovaries, a method for producing Crustacean hatched larvae, and Crustaceans, which enable stable production of hatched larvae. It also provides a method for producing Crustaceans, which enables stable production of Crustaceans by culturing such hatched larvae. [Means for solving the problem]

[0005] One aspect of the present disclosure provides a method for regulating ovarian maturation in Crustaceans, comprising a rearing step of adjusting the rearing temperature of one or more individual Crustaceans to adjust the frequency of ovarian maturation. Another aspect of the present disclosure provides a method for regulating ovarian maturation in Crustaceans, comprising a rearing step of adjusting the rearing temperature of a population of Crustaceans whose average weight has reached a spawning weight to adjust the frequency of ovarian maturation. The method for regulating ovarian maturation in Crustaceans can advance or delay the timing of mating and spawning in female Crustaceans by adjusting the rearing temperature. This allows the maturation frequency of the Crustaceans to be adjusted, thereby adjusting the timing for obtaining hatched larvae. Therefore, hatched larvae can be obtained stably.

[0006] One aspect of the present disclosure provides a method for producing Crustacean hatched larvae, the method comprising: a preparation step of preparing one or more Crustacean individuals that have reached a weight sufficient for spawning; and a rearing step of rearing the individuals so that the immature and mature stages occur at any desired times, and obtaining hatched larvae from fertilized eggs laid by the individuals, wherein the rearing step adjusts the frequency of ovarian maturation by regulating the rearing temperature of the individuals. Another aspect of the present disclosure provides a method for producing Crustacean hatched larvae, the method comprising: a preparation step of preparing a population of Crustaceans whose average weight has reached a weight sufficient for spawning; and a rearing step of rearing the population of Crustaceans so that the immature and mature stages occur at any desired times, and obtaining hatched larvae from fertilized eggs laid by the population of Crustaceans, wherein the rearing step adjusts the frequency of ovarian maturation by regulating the rearing temperature of the population of Crustaceans.

[0007] The method for producing hatched crustacean larvae involves adjusting the maturation frequency of the crustacean ovaries by adjusting the rearing temperature during the rearing process when rearing crustaceans that have reached a weight at which they can lay eggs. By adjusting the maturation frequency of the crustacean ovaries, it is possible to advance or delay the timing of mating and egg-laying of female crustaceans. This adjusts the frequency of the immature and mature stages of the crustaceans, and allows for the desired adjustment of the timing at which hatched larvae are obtained from eggs laid by the crustaceans. Therefore, hatched larvae can be obtained stably.

[0008] One aspect of the present disclosure provides a method for producing Crustacean hatched larvae, comprising: a preparation step of preparing one or more individual Crustaceans that have reached a weight sufficient for spawning; and a rearing step of rearing the individuals so that the immature and mature stages occur at any desired time, and obtaining hatched larvae from fertilized eggs laid by the individuals, wherein the rearing temperature for the individuals is maintained at 17 to 23°C from the first to fourth ovarian maturation steps. Another aspect of the present disclosure provides a method for producing Crustacean hatched larvae, comprising: a preparation step of preparing a population of Crustaceans whose average weight has reached a weight sufficient for spawning; and a rearing step of rearing the population of Crustaceans so that the immature and mature stages occur at any desired time, and obtaining hatched larvae from fertilized eggs laid by the individuals, wherein the rearing temperature for the population of Crustaceans is maintained at 17 to 23°C from the first to fourth ovarian maturation steps.

[0009] In the method for producing hatched crustacean larvae, when crustaceans that have reached a weight sufficient for egg-laying are reared, the rearing temperature for the individuals is maintained at 17 to 23°C from the first to fourth ovarian maturation in the rearing process. By maintaining the rearing temperature at 17 to 23°C, the frequency of ovarian maturation can be adjusted. By adjusting the frequency of ovarian maturation in crustaceans, the timing of mating and egg-laying can be advanced or delayed. This adjusts the frequency of immature and mature stages in crustaceans, and allows for the timing of obtaining hatched larvae obtained from eggs laid by crustaceans to be adjusted as desired. Therefore, hatched larvae can be obtained stably.

[0010] One aspect of the present disclosure provides a method for producing Crustaceans, comprising a culturing step of obtaining Crustaceans by culturing hatched larvae obtained by the above-described production method. The method for producing Crustaceans involves culturing the hatched larvae of Crustaceans obtained by the above-described method for producing Crustacean hatched larvae, and therefore, Crustaceans can be obtained stably.

[0011] One aspect of the present disclosure provides crustaceans obtained by rearing one or more crustacean individuals that have reached a weight sufficient for spawning at a rearing temperature of 21°C or less for a cumulative period of 45 days or more. Because the crustaceans are reared at low temperatures, the frequency of ovarian maturation can be promoted by raising the rearing temperature. Therefore, the frequency of ovarian maturation can be adjusted by adjusting the rearing temperature, and newly hatched larvae can be obtained stably. Another aspect of the present disclosure provides crustaceans obtained by rearing a population of crustaceans whose average weight has reached a weight sufficient for spawning at a rearing temperature of 21°C or less for a cumulative period of 45 days or more. Because the population of crustaceans is reared at low temperatures, the frequency of ovarian maturation can be promoted by raising the rearing temperature. Therefore, the frequency of ovarian maturation can be adjusted by adjusting the rearing temperature, and newly hatched larvae can be obtained stably overall. [Effects of the Invention]

[0012] The present disclosure can provide a method for adjusting the maturation of Crustacean ovaries, a method for producing Crustacean hatched larvae, and Crustaceans, which enable stable production of hatched larvae. The present disclosure can also provide a method for producing Crustaceans, which enables stable production of Crustaceans by culturing such hatched larvae. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the maturation interval of the ovaries of individual vannamei shrimp when reared at a temperature of 23° C. or 27° C. DETAILED DESCRIPTION OF THE INVENTION

[0014] Several embodiments of the present disclosure are described below. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The upper or lower limit of the numerical ranges in the present disclosure may be replaced with any value shown in the examples. Numerical ranges obtained by arbitrarily combining the individually listed upper and lower limit values ​​are also included in the present disclosure. Unless otherwise specified, the materials or components exemplified in the present disclosure can be used alone or in combination of two or more. The symbol "~" used in a numerical range indicates a numerical range that includes the upper and lower limit values. For example, "X~Y" indicates a numerical range of "greater than or equal to X and less than or equal to Y."

[0015] <Method for adjusting maturation of crustacean ovaries> A method for adjusting the maturation of Crustacean ovaries according to one embodiment includes a rearing step of adjusting the rearing temperature of one or more individual Crustaceans (hereinafter sometimes simply referred to as "individuals") to adjust the frequency of ovarian maturation. Prior to the rearing step, the method may include a preparation step of preparing the individual capable of spawning.

[0016] In one example of this embodiment, the method includes a rearing step of adjusting the rearing temperature of the population of Crustaceans to control the frequency of ovarian maturation. Prior to the rearing step, the method may include a preparation step of preparing the population capable of spawning.

[0017] In the present disclosure, a population of crustaceans may be 5 or more, 6 or more, 10 or more, 32 or more, 100 or more, 1,000 or more, 10,000 or more, or 100,000 or more. The upper limit may be within the range that can be reared in the rearing facility, for example, 100 million or less, or 10 million or less. By adjusting the maturation frequency in the population of crustaceans, maturation can be adjusted to any frequency, resulting in a stable harvest of eggs.

[0018] The rearing water is water or an aqueous solution contained in an aquarium for cultivating crustaceans and used for rearing the crustaceans. The rearing water may contain at least one selected from the group consisting of freshwater, seawater, and brackish water. An appropriate water can be selected depending on the type of crustacean being reared. Seawater and brackish water may be prepared using artificial seawater. The type of rearing water may be changed depending on the rearing period from egg to shipping size.

[0019] The individuals in the rearing step are one or more individual crustaceans that have reached a weight sufficient for spawning. The population in the rearing step is a population of crustaceans that have reached a weight sufficient for spawning. In a preparation step prior to the rearing step, one or more individual crustaceans that have reached a weight sufficient for spawning or a population of crustaceans are prepared. The crustaceans may include crabs and shrimp. Crabs may include Japanese freshwater crab, Japanese red crab, snow crab, red snow crab, Shanghai crab, Japanese mitten crab, stone crab, blue crab, hairy crab, and flower crab. Shrimp of the order Decapoda are preferred, and the order Decapoda includes the superfamily Primate and the superfamily Penaeidae. The superfamily Primate includes, for example, saur shrimp and aquatoid. The superfamily Penaeidae includes the family Penaeidae and the family Penaeidae. Shrimp of the family Penaeidae include, for example, stone shrimp. Shrimp of the Penaeidae family include, for example, shrimp of the genera Farfantepenaeus, Fenneropenaeus, Litopenaeus, Marsupenaeus, Melicertus, Metapenaeopsis, Metapenaeus, Penaeus, Trachypenaeus, and Xiphopenaeus.

[0020] Among the Penaeidae family, for example, edible shrimp include kuruma shrimp (Marsupenaeus japonicus), southern kuruma shrimp (Melicertus canaliculatus), black tiger shrimp (Penaeus monodon), Korean shrimp (Penaeus chinensis), giant tiger shrimp (Penaeus semisulcatus), palm shrimp (Penaeus latisulcatus), Indian shrimp (Fenneropenaeus indicus), Yoshino shrimp (Metapenaeus ensis), Japanese crested shrimp (Metapenaeus intermedius), Penaeus occidentalis, blue shrimp (Penaeus stylirostris), red-tail shrimp (Penaeus pencicillatus), and whitenamei shrimp (Litopenaeus vannamei).

[0021] The crustacean in the present disclosure may include the Penaeidae family, the Litopenius genus, and in particular the white shrimp (Litopenaeus vannamei). The white shrimp can be suitably used as the crustacean for adjusting the ovarian maturation frequency in this embodiment.

[0022] After growing, only female crustaceans that have reached a certain egg-laying weight can have their ovaries mature and lay eggs. The egg-laying weight of an individual may be 30 g or more, 35 g or more, 40 g or more, or 50 g or more. Such individuals can further improve the efficiency of ovarian maturation. The egg-laying weight of crustaceans may be 100 g or less. An example of the egg-laying weight is 30 to 100 g.

[0023] After growing, only female crustaceans that have reached a certain total length suitable for spawning can have their ovaries mature and spawn. The total length suitable for spawning of crustaceans may be 170 mm or more, 180 mm or more, or 190 mm or more. Such individuals can further improve the efficiency of ovarian maturation. The total length suitable for spawning of crustaceans may be 240 mm or less. An example of the total length suitable for spawning is 170 to 240 mm.

[0024] The age of the individuals that have reached the egg-laying weight and are prepared in the preparation step may be 25 weeks or more, 30 weeks or more, 35 weeks or more, or 40 weeks or more. Such individuals can further improve the efficiency of ovarian maturation. The egg-laying age of crustaceans may be 60 weeks or less. The age of the individuals that have reached the egg-laying weight may be 25 to 60 weeks.

[0025] The preparation step may include a preliminary rearing step of rearing crustaceans that have not yet reached the weight required for egg-laying until they reach the weight required for egg-laying. The crustaceans that have not yet reached the weight required for egg-laying may be individuals that are young (e.g., less than 25 weeks old) and weigh less than 30 g. Such individuals may be obtained by rearing hatched larvae, or may be obtained by a different route.

[0026] In the rearing process, it is not necessary to perform eyestalk treatment to induce ovarian maturation. Eyestalk treatment is a process in which the eyestalks of crustaceans are removed to secrete hormones that induce ovarian maturation, thereby forcing the ovaries to mature. By not performing eyestalk treatment, the lifespan of crustaceans can be extended, allowing them to be used for breeding over a long period of time. In the rearing process, lugworm feeding may be performed to induce ovarian maturation in crustaceans. Feeding lugworms promotes ovarian maturation in crustaceans.

[0027] In the present disclosure, maturation refers to the maturation of the ovaries in females. Crustaceans that have reached a weight sufficient for spawning begin to undergo ovarian maturation after molting. When ovarian maturation begins, the oviducts begin to elongate, and as ovarian maturation progresses, the ovaries develop significantly. The stage of ovarian maturation is evaluated into four stages, I, II, III, and IV, based on the degree of ovarian development, and maturation and fertilization become possible when the ovaries reach stages III and IV. In the present disclosure, stages I and II are defined as immature stages, and stages III and IV are defined as mature stages. The stage of ovarian maturation in crustaceans can be evaluated by visually checking the size of the ovaries. The rearing process may be a process of rearing individuals so that the immature and mature stages occur at any desired stage.

[0028] Mating occurs when a mature female crustacean, whose ovaries have reached stages III and IV, is placed in the same tank as a male crustacean, and the male attaches spermatophores to the female's abdomen. The mating success rate can be calculated by calculating the ratio of the number of females in the male's tank to the number of females with attached spermatophores. Females with attached spermatophores can fertilize their own eggs with the sperm in the spermatophores to obtain fertilized eggs. After fertilization, the female releases the fertilized eggs into the tank. During the rearing process, some females may not be able to attach spermatophores and fail to mate. Regardless of whether the eggs are fertilized, females with fully mature ovaries will release their eggs into the tank. When a female with mature ovaries releases eggs, the ovarian maturation stage returns to immature stage I. Some females may not release eggs and their ovaries may regress. The crustacean can then cycle through the immature and mature stages in the same way.

[0029] In the rearing process, the mating success rate may be 20% or more, 40% or more, 60% or more, or 80% or more. If the mating success rate is within the above range, the egg quality can be maintained at a higher level, and the efficiency of obtaining hatched larvae can be improved. An example of the range of the mating success rate may be 20 to 100%, and the lower limit of the range of the mating success rate may be 40%, and the upper limit of the range of the mating success rate may be 80%. The range of the mating success rate may be, for example, 40 to 80%.

[0030] In the rearing process, the rearing temperature of the individual animals is adjusted to control the frequency of ovarian maturation. The rearing temperature can be adjusted by the temperature of the rearing water. Crustaceans have an optimal rearing temperature for ovarian maturation based on their natural environment, such as their place of origin. For example, for the tropical whiteleg shrimp, a rearing temperature of 28 to 32°C is optimal for ovarian maturation. On the other hand, the further the rearing temperature of whiteleg shrimp deviates from 28 to 32°C, the less suitable the rearing temperature becomes for ovarian maturation. Therefore, by adjusting the rearing temperature in the rearing process, ovarian maturation can be accelerated or delayed. This allows the timing of ovarian maturation of crustaceans to be controlled at any time, allowing for a stable supply of crustacean hatched larvae according to demand. Temperature control devices such as coolers and heaters can be used to adjust the rearing temperature.

[0031] When crustaceans are reared in rearing water with an average temperature of 25°C for 15 days, the average ovarian maturation rate may be 7-13% / day, or may be 8-12% / day. The frequency of ovarian maturation in such crustaceans is sufficiently suppressed. Therefore, deterioration of egg quality due to repeated ovarian maturation can be suppressed. The ovarian maturation rate is the ratio of the number of crustaceans whose ovaries have matured in one day to the total number of crustaceans being reared. The number of ovarianly matured individuals can be determined by visually observing the crustaceans. The average ovarian maturation rate is the arithmetic mean of the ovarian maturation rate for each day. The temperature measurement interval is not particularly limited and may be, for example, 1 second to 12 hours. The average temperature is the arithmetic mean of each measurement value.

[0032] When crustaceans are reared in rearing water with an average temperature of 23°C for 15 days, the average ovarian maturation rate may be 1-5% / day, or may be 2-4% / day. This prevents the crustacean ovarian maturation frequency from becoming too high. Therefore, deterioration of egg quality due to repeated ovarian maturation can be sufficiently suppressed.

[0033] The average ovarian maturation rate may be 0% when crustaceans are reared for 15 days in rearing water with an average temperature of 21°C or less. In other words, the ovaries of crustaceans may not be mature at temperatures of 21°C or less. By preventing the ovaries from maturing, deterioration of egg quality due to repeated ovarian maturation can be further suppressed. Since the ovaries of such crustaceans do not mature even when reared, they can be reared for a long period of time while suppressing deterioration of egg quality when the ovaries mature. This allows for a stable production of hatched larvae over a long period of time.

[0034] When crustaceans are reared in rearing water at an average temperature of 27°C for 15 days, the average ovarian maturation rate may be 15-20% / day, or even 16-18% / day. Such crustaceans have an accelerated ovarian maturation frequency. Therefore, it is possible to accelerate the maturation of crustaceans whose ovarian maturation frequency had previously been suppressed. By adjusting the temperature in this way, the timing of ovarian maturation can be controlled. For example, if the ovarian immaturity, maturation, and spawning are more favorable than expected and the number of hatched larvae is likely to be excessive, the temperature of the rearing water can be lowered. If the ovarian immaturity, maturation, and spawning are less favorable than expected and the number of hatched larvae is likely to be insufficient, the temperature of the rearing water can be raised. By controlling the number of hatched larvae obtained in this way, hatched larvae can be obtained stably.

[0035] In the rearing process, the ovarian maturation interval of each individual Crustacean may be 10 days or more on average when the ovarian maturation interval is checked daily. The term "average" here refers to the arithmetic mean value of multiple ovarian maturation intervals when one individual undergoes multiple ovarian maturation cycles. When an individual undergoes a single ovarian maturation cycle, the average value is the sum of the number of days for that single ovarian maturation cycle and either the ovarian immaturity period before or after ovarian maturation. The ovarian maturation interval refers to the number of days from when the ovarian maturation of the reared Crustacean reaches maturity stage III or IV, until spawning occurs, the ovarian maturation returns to immaturity stage I, and the ovarian maturation period returns to stage III or IV. In the rearing process, the ovarian maturation interval of the individual may be 10 days or more, 11 days or more, 12 days or more, 13 days or more, or 14 days or more on average. By keeping the ovarian maturation interval within the above range, the ovarian maturation interval can be extended, thereby suppressing the frequency of ovarian maturation in Crustaceans. This allows the parent crustaceans to be used for a longer period of time, improving the efficiency of obtaining hatched larvae. The maturation interval of the crustacean ovaries may be 20 days or less on average. An example of the maturation interval of the crustacean ovaries may be 10 to 20 days. The longer the maturation period of the ovaries, the longer the period over which hatched larvae can be produced.

[0036] The average number of days required for ovarian maturation in Crustaceans may be six days or more, seven days or more, or eight days or more. The number of days required for ovarian maturation refers to the number of days required for Crustaceans to reach maturity stage III or IV. The number of days required for ovarian maturation can be expressed as the number of consecutive days required for ovarian maturation when checking each individual's ovaries for maturity daily. For example, if the ovaries mature one day after the start of rearing, continue to mature for two to six days after rearing, and remain unmatured seven days later, the number of days required for ovarian maturation is six days. The average is the arithmetic mean of the number of days required for multiple ovarian maturation in a single individual. Keeping the number of days required for ovarian maturation within the above range extends the ovarian maturation period, making it easier to control the timing of fertilization. Furthermore, the frequency of ovarian maturation in Crustaceans can be suppressed. This allows the use of parent Crustaceans for a longer period of time, improving the efficiency of obtaining hatched larvae. The average number of days required for ovarian maturation in Crustaceans may be ten days or less. The maturation period of the crustacean ovaries may be, for example, 6 to 10 days.

[0037] The average number of days of ovarian immaturity in Crustaceans may be 5 days or more, 6 days or more, or 7 days or more. The number of days of ovarian immaturity refers to the number of days that Crustaceans are in immature stage I or II. The number of days of ovarian immaturity can be expressed as the number of consecutive days of ovarian immaturity when the maturation of each individual's ovaries is confirmed daily. For example, if the ovaries mature one day after the start of rearing, remain immature for two to six days after rearing, and then mature again seven days later, the number of days of ovarian immaturity is 5 days. The average is the arithmetic mean value of the number of days of ovarian immaturity in multiple ovaries when one individual undergoes multiple ovarian maturation cycles. By keeping the number of days of ovarian immaturity within the above range, the interval between ovarian maturation can be extended, thereby suppressing the frequency of ovarian maturation in Crustaceans. This allows the use of parent Crustaceans for a long period of time and allows for a sufficiently stable production of hatched larvae. The average number of days of ovarian immaturity in Crustaceans may be 10 days or less. An example of the number of days for which the ovaries of crustaceans are immature is 5 to 10 days.

[0038] The number of rearing days in the rearing step may be a cumulative total of 90 days or more, 100 days or more, or 110 days or more. By keeping the number of rearing days within this range, the maturation frequency of the crustacean ovaries can be further delayed, and newly hatched larvae can be stably obtained over a long period of time. The number of rearing days in the rearing step may be a cumulative total of 200 days or less. An example of the number of rearing days may be a cumulative total of 90 to 200 days.

[0039] In the rearing process, the rearing temperature may be maintained at 20 to 24°C, or 21 to 23°C. By rearing crustaceans within this temperature range, for example, tropical crustaceans such as whiteleg shrimp, can be reared while suppressing the frequency of ovarian maturation because the temperature is lower than the optimal rearing temperature. This allows the interval between ovarian maturation to be extended, making it possible to obtain hatched larvae over a long period of time. This therefore improves the efficiency of obtaining hatched larvae.

[0040] In the rearing process, the crustaceans may be reared in a first period at an average rearing temperature T1, and then reared in a second period at an average rearing temperature T2 that is 2°C or more higher than the average rearing temperature T1, thereby maturing the ovaries of the crustaceans. By rearing at a low temperature and then at a high temperature in this way, it is possible to promote the maturation of the ovaries of the crustaceans, which had been inhibited at first. Alternatively, the crustaceans may be reared in multiple tanks, one at a high temperature and the other at a low temperature, and after the quality of the eggs of the crustaceans reared at the high temperature has deteriorated, they may be replaced with crustaceans whose ovarian maturation has been inhibited at a low temperature.

[0041] When rearing in high-temperature rearing water during the rearing process, the daily temperature change should be 0°C or more. The daily temperature change may be 2°C or less, 1.5°C or less, 1°C or less, or 0.5°C or less. Gradual changes in rearing temperature cause less damage to crustaceans. Therefore, one batch of crustaceans can be used over a long period of time, allowing for a stable production of hatched larvae. This also reduces the number of times crustaceans need to be transported. If the daily temperature change exceeds 2°C, the crustaceans may be damaged by the sudden change in rearing environment.

[0042] The average temperature T1 may be 19°C or less, and the average temperature T2 may be 24°C or more. Alternatively, the average temperature T1 may be 17°C or less, and the average temperature T2 may be 25°C or more. Crustaceans may die if the average temperature T1 is below 15°C, so a temperature of 15°C or more is preferable. Crustaceans may die if the average temperature T2 is above 32°C, so a temperature of 32°C or less is preferable. By keeping the average temperatures T1 and T2 within the above ranges, most crustaceans' ovaries do not mature when reared at the average temperature T1, and then rearing at the average temperature T2 can promote ovarian maturation. This allows crustaceans to be reared in multiple tanks with high and low temperatures in advance. After the ovaries of crustaceans reared at 24°C or higher have matured multiple times and the egg quality has decreased, the ovaries can be replaced with crustaceans with unmature ovaries reared at 19°C or less, allowing the ovaries to mature again. Therefore, a single batch of crustaceans can be used over a long period of time, allowing for a stable production of hatched larvae. Furthermore, the number of times crustaceans need to be transported can be reduced. From a similar viewpoint, the difference between the average temperature T1 and the average temperature T2 may be 5°C or more, 7°C or more, or 9°C or more. The difference between the average temperature T1 and the average temperature T2 may be 15°C or less. For example, the difference between the average temperature T1 and the average temperature T2 may be 2 to 15°C.

[0043] The first period for rearing at the average temperature T1 may be 70 days or more, 80 days or more, or 90 days or more. By keeping the period for rearing at the average temperature T1 within the above range, the maturation of the crustacean ovaries can be delayed by 2 to 3 months. This allows one batch of crustaceans to be used for a longer period of time, allowing for a stable production of hatched larvae. The period for rearing at the average temperature T1 may be 180 days or less. An example of the period for rearing at the average temperature T1 may be 70 to 180 days.

[0044] The average maturation rate of the ovaries of Crustaceans reared in rearing water at an average temperature T2 may be 1.5 times or more, 1.6 times or more, or even 1.7 times or more than the average maturation rate of the ovaries of Crustaceans reared in rearing water at an average temperature T1. When the ratio of the average maturation rate of the ovaries of Crustaceans reared at an average temperature T2 to the average maturation rate of the ovaries of Crustaceans reared at an average temperature T1 is within this range, the maturation of the ovaries of the Crustaceans can be sufficiently promoted. Note that the average maturation rate of the ovaries of Crustaceans reared at an average temperature T2 may be 2.5 times or less than the average maturation rate of the ovaries of Crustaceans reared at an average temperature T1.

[0045] The rearing temperature may be set to 25°C or below for 1 to 90 days after the start of rearing, and 27°C or above for 91 to 180 days. That is, the rearing temperature may be set to 25°C or below for the first period, and 27°C or above for the second period. By providing a temperature difference between the first and second halves of the rearing period, ovarian maturation can be suppressed and then accelerated. By rearing in this manner, hatched larvae can be obtained over a longer period. Furthermore, breeding can be carried out between the generation reared at 27°C or above and the generation in which ovarian maturation is delayed. Such crossbreeding is advantageous for improving varieties.

[0046] In the rearing process, hatched larvae may be obtained from the laid fertilized eggs. In this case, hatched larvae are obtained from eggs laid in an aquarium. The hatching rate can be determined by measuring the number of laid eggs and the number of hatched larvae. The number of laid eggs can be determined by taking an image of a portion of the aquarium, counting the number of eggs in the image, and converting this number to the total amount in the aquarium. The number of laid eggs and the number of hatched eggs can be measured using, for example, an "XperCounter2 (product name)" (manufactured by XpertSea).

[0047] The number of eggs obtained per female may be 150,000 to 600,000, 200,000 to 550,000, or 250,000 to 500,000. When the number of eggs per female is within the above range, the maturation of the female's ovaries can be sufficiently promoted. "Per female" refers to one individual crustacean as described above.

[0048] If the average number of eggs per female obtained during the cumulative period from the start of rearing to 90 days is Q1, and the average number of eggs per female obtained during the cumulative period from 91 to 180 days is Q2, then Q1 ≦ Q2 may be satisfied. When Q1 ≦ Q2, the ovarian maturation rate does not decrease even when crustaceans are reared over a long period of time, and females can lay many eggs even after a cumulative period of 91 to 180 days from rearing. The average numbers Q1 and Q2 here refer to the average number obtained by dividing the total number of eggs obtained per female reared during each period by the number of days on which eggs could be collected.

[0049] Q1 may be 250,000 to 400,000, or 300,000 to 350,000. Q2 may be 300,000 to 500,000, or 350,000 to 480,000. When Q1 and Q2 are within these ranges, the ovaries can be sufficiently matured even when the crustaceans are reared for a long period of time.

[0050] The number of hatched larvae obtained per day per female may be 30,000 to 550,000, 100,000 to 500,000, or 200,000 to 450,000. By keeping the number of hatched larvae obtained per day per female within the above range, the mating success rate of the females can be improved while the mating rate can be improved. Furthermore, the egg quality can be maintained at a higher level, and the efficiency of obtaining hatched larvae can be improved.

[0051] During a cumulative period of 91 to 180 days from the start of rearing the individuals in the rearing step, the number of hatched larvae obtained per day per female may be 100,000 or more, 200,000 or more, or even 300,000 or more. By keeping the number of hatched larvae obtained per day per female within this range, a sufficient number of hatched larvae can be obtained even when reared over a long period of time. The number of hatched larvae obtained per day per female may be 1,000,000 or less.

[0052] In the rearing process, when the average number of hatched larvae per female obtained during the cumulative period from the start of rearing of the individuals up to 90 days is P1, and the average number of hatched larvae obtained during the cumulative period from 91 to 180 days is P2, P1 ≦ P2 may be satisfied. When P1 ≦ P2, the quality of the eggs does not deteriorate even when the crustaceans are reared over a long period, and a large number of hatched larvae can be obtained even after the period from 91 to 180 days from the start of rearing. The average numbers P1 and P2 here refer to the average number of larvae obtained by dividing the total number of hatched larvae obtained per female reared during each period by the number of days on which hatched larvae could be obtained.

[0053] P1 may be 150,000 to 300,000 fish, or 200,000 to 250,000 fish. P2 may be 200,000 to 500,000 fish, or 300,000 to 400,000 fish. By keeping P1 and P2 within these ranges, it is possible to maintain a high mating success rate even for female individuals that have been raised for a long period of time, and to obtain a sufficient number of hatched larvae.

[0054] P2 / P1 may be 1.5 or more, 1.6 or more, 1.7 or more, or 1.8 or more. When P2 / P1 is within this range, a high mating success rate can be maintained even for female individuals reared for a long period of time, and a sufficient number of hatched larvae can be obtained.

[0055] The hatching rate may be 60% or more, 70% or more, or 80% or more. If the hatching rate is within the above range, the efficiency of obtaining hatched larvae can be improved. An example of the hatching rate may be 60 to 100%.

[0056] <First embodiment of the method for producing hatched crustacean larvae> The method for producing hatched crustacean larvae in the first embodiment includes a preparation step of preparing one or more crustacean individuals that have reached a weight sufficient for egg-laying, and a rearing step of rearing the individuals so that the immature and mature stages of the ovaries occur at any desired time, and obtaining hatched larvae from the fertilized eggs laid by the individuals.

[0057] One example of this embodiment includes a preparation step of preparing a population of crustaceans whose average weight has reached a weight at which they can lay eggs, and a rearing step of rearing the population of crustaceans so that the immature and mature stages are at any desired times, and obtaining hatched larvae from fertilized eggs laid by the population of crustaceans, and in the rearing step, the rearing temperature of the population of crustaceans may be adjusted to adjust the frequency of ovarian maturation.

[0058] The rearing water may be the same as that described in the embodiment of the maturation control method. In the preparation step, individual crustaceans are prepared in the same manner as described in the embodiment of the maturation control method. Furthermore, a preliminary rearing step, as described in the embodiment of the maturation control method, may be performed before the rearing step.

[0059] The egg-laying weight of the individuals prepared in the preparation step prior to the rearing step may be 30 g or more, 35 g or more, 40 g or more, or 50 g or more. Such individuals can further improve the efficiency of ovarian maturation. The egg-laying weight of the crustaceans may be 100 g or less. An example of the egg-laying weight is 30 to 100 g. A suitable crustacean in this embodiment is, for example, the whiteleg shrimp.

[0060] In the rearing step, the individuals prepared in the preparation step are reared so that the ovarian immaturity and maturity periods occur at any desired time. In the rearing step, the rearing temperature is adjusted to adjust the ovarian maturation frequency, as in the embodiment of the maturation control method described above. This allows the timing of the individual's immaturity and maturity periods to be adjusted, and the immaturity and maturity periods can be set at any desired time. Therefore, newly hatched larvae can be produced stably.

[0061] The rearing step in this embodiment may be the same as the rearing step in the embodiment of the maturation control method described above. That is, in the rearing step, the Crustacean individuals may be reared so that their ovaries repeatedly undergo immaturity and maturation. The maturation success rate, average ovarian maturation rate, ovarian maturation interval, number of days to maturity, number of days to non-maturity, cumulative number of rearing days, and rearing temperature of the Crustaceans in the rearing step can be directly applied to the explanations of the embodiment of the maturation control method described above.

[0062] In the rearing step, the ovarian maturation interval of each individual Crustacean may be 10 days or more on average when the ovarian maturation interval is checked every day. The maturation interval is calculated in the same manner as in the embodiment of the maturation control method described above. In the rearing step, the ovarian maturation interval of each individual may be 10 days or more on average, 11 days or more, 12 days or more, 13 days or more, or 14 days or more. By keeping the ovarian maturation interval within the above range, the ovarian maturation interval can be lengthened, thereby suppressing the ovarian maturation frequency of Crustaceans. This allows the parent Crustaceans to be used for a longer period of time, thereby improving the efficiency of obtaining hatched larvae. The ovarian maturation interval of Crustaceans may be 20 days or less on average. An example of the ovarian maturation interval of Crustaceans may be 10 to 20 days. The longer the ovarian maturation period, the longer the period in which hatched larvae can be produced.

[0063] The number of days required for maturation of Crustacean ovaries may be, on average, 6 days or more, 7 days or more, or 8 days or more. By keeping the number of days required for maturation of ovaries within the above range, the maturation period of ovaries is extended, making it easier to control the timing of fertilization. In addition, the frequency of maturation of Crustacean ovaries can be suppressed. This allows the parent Crustaceans to be used for a longer period of time, improving the efficiency of obtaining hatched larvae. The number of days required for maturation of Crustacean ovaries may be, on average, 10 days or less. An example of the number of days required for maturation of Crustacean ovaries may be 6 to 10 days.

[0064] The number of days of immaturity of the ovaries of Crustaceans may be 5 days or more, 6 days or more, or 7 days or more on average. By keeping the number of days of immaturity of the ovaries within the above range, the interval between ovarian maturation can be lengthened, and the frequency of maturation of the ovaries of Crustaceans can be suppressed. This allows the parent crustaceans to be used for a long period of time, and hatched larvae can be obtained sufficiently stably. The number of days of immaturity of the ovaries of Crustaceans may be 10 days or less on average. An example of the number of days of immaturity of the ovaries of Crustaceans may be 5 to 10 days.

[0065] The number of rearing days in the rearing step may be a cumulative total of 90 days or more, 100 days or more, or 110 days or more. By keeping the number of rearing days within this range, the maturation frequency of the crustacean ovaries can be further delayed, and newly hatched larvae can be stably obtained over a long period of time. The number of rearing days in the rearing step may be a cumulative total of 200 days or less. An example of the number of rearing days may be a cumulative total of 90 to 200 days.

[0066] In the rearing process, the rearing temperature may be maintained at 20 to 24°C, or 21 to 23°C. By rearing crustaceans within this temperature range, for example, tropical crustaceans such as whiteleg shrimp, can be reared while suppressing the frequency of ovarian maturation because the temperature is lower than the optimal rearing temperature. This allows the interval between ovarian maturation to be extended, making it possible to obtain hatched larvae over a long period of time. This therefore improves the efficiency of obtaining hatched larvae.

[0067] In the rearing process, the crustaceans may be reared in a first period at an average rearing temperature T1, and then reared in a second period at an average rearing temperature T2 that is 2°C or more higher than the average rearing temperature T1, thereby maturing the ovaries of the crustaceans. By rearing at a low temperature and then at a high temperature in this way, it is possible to promote the maturation of the ovaries of the crustaceans, which had been inhibited at first. Alternatively, the crustaceans may be reared in multiple tanks, one at a high temperature and the other at a low temperature, and after the quality of the eggs of the crustaceans reared at the high temperature has deteriorated, they may be replaced with crustaceans whose ovarian maturation has been inhibited at a low temperature.

[0068] When rearing in high-temperature rearing water during the rearing process, the daily temperature change should be 0°C or more. The daily temperature change may be 2°C or less, 1.5°C or less, 1°C or less, or 0.5°C or less. Gradual changes in rearing temperature cause less damage to crustaceans. Therefore, one batch of crustaceans can be used over a long period of time, allowing for a stable production of hatched larvae. This also reduces the number of times crustaceans need to be transported. If the daily temperature change exceeds 2°C, the crustaceans may be damaged by the sudden change in rearing environment.

[0069] The average temperature T1 may be 19°C or less, and the average temperature T2 may be 24°C or more. Alternatively, the average temperature T1 may be 17°C or less, and the average temperature T2 may be 25°C or more. Crustaceans may die if the average temperature T1 is below 15°C, so a temperature of 15°C or more is preferable. Crustaceans may die if the average temperature T2 is above 32°C, so a temperature of 32°C or less is preferable. By keeping the average temperatures T1 and T2 within the above ranges, most crustaceans' ovaries do not mature when reared at the average temperature T1, and then rearing at the average temperature T2 can promote ovarian maturation. This allows crustaceans to be reared in multiple tanks with high and low temperatures in advance. After the ovaries of crustaceans reared at 24°C or higher have matured multiple times and the egg quality has decreased, the ovaries can be replaced with crustaceans with unmature ovaries reared at 19°C or less, allowing the ovaries to mature again. Therefore, a single batch of crustaceans can be used over a long period of time, allowing for a stable production of hatched larvae. Furthermore, the number of times crustaceans need to be transported can be reduced. From a similar viewpoint, the difference between the average temperature T1 and the average temperature T2 may be 5°C or more, 7°C or more, or 9°C or more. The difference between the average temperature T1 and the average temperature T2 may be 15°C or less. For example, the difference between the average temperature T1 and the average temperature T2 may be 2 to 15°C.

[0070] The first period for rearing at the average temperature T1 may be 70 days or more, 80 days or more, or 90 days or more. By keeping the period for rearing at the average temperature T1 within the above range, the maturation of the crustacean ovaries can be delayed by 2 to 3 months. This allows one batch of crustaceans to be used for a longer period of time, allowing for a stable production of hatched larvae. The period for rearing at the average temperature T1 may be 180 days or less. An example of the period for rearing at the average temperature T1 may be 70 to 180 days.

[0071] The average maturation rate of the ovaries of Crustaceans reared in rearing water at an average temperature T2 may be 1.5 times or more, 1.6 times or more, or even 1.7 times or more than the average maturation rate of the ovaries of Crustaceans reared in rearing water at an average temperature T1. The average maturation rate is calculated in the same manner as in the embodiment of the maturation control method described above. When the ratio of the average maturation rate of the ovaries of Crustaceans reared at an average temperature T2 to the average maturation rate of the ovaries of Crustaceans reared at an average temperature T1 is within this range, the maturation of the ovaries of the Crustaceans can be sufficiently promoted. Note that the average maturation rate of the ovaries of Crustaceans reared at an average temperature T2 may be 2.5 times or less than the average maturation rate of the ovaries of Crustaceans reared at an average temperature T1.

[0072] In the rearing step, hatched larvae are obtained from the fertilized eggs laid by the individuals. During a cumulative period of 91 to 180 days from the start of rearing, the number of hatched larvae obtained per day per female may be 100,000 or more, 200,000 or more, or even 300,000 or more. By keeping the number of hatched larvae obtained within this range, a sufficient number of hatched larvae can be obtained even after long-term rearing. The number of hatched larvae obtained per day per female may be 1,000,000 or less.

[0073] When the average number of hatched larvae per female obtained in the cumulative period from the start of rearing to 90 days is P1, and the average number of hatched larvae obtained in the cumulative period from 91 to 180 days is P2, P1 ≦ P2 may be satisfied. When P1 ≦ P2, egg quality does not deteriorate even when crustaceans are reared over a long period of time, and a large number of hatched larvae can be obtained even 91 to 180 days after rearing begins.

[0074] P1 may be 150,000 to 300,000 fish, or 200,000 to 250,000 fish. P2 may be 200,000 to 500,000 fish, or 300,000 to 400,000 fish. By keeping P1 and P2 within these ranges, it is possible to maintain a high mating success rate even for female individuals that have been raised for a long period of time, and to obtain a sufficient number of hatched larvae.

[0075] P2 / P1 may be 1.5 or more, 1.6 or more, 1.7 or more, or 1.8 or more. When P2 / P1 is within this range, a high mating success rate can be maintained even for female individuals reared for a long period of time, and a sufficient number of hatched larvae can be obtained.

[0076] The other details regarding the rearing process can be applied as is to the details of the embodiment of the maturation control method described above.

[0077] <Second embodiment of the method for producing hatched crustacean larvae> The method for producing crustacean hatched larvae according to the second embodiment includes a preparation step of preparing one or more crustacean individuals that have reached a weight sufficient for egg-laying, and a rearing step of rearing the individuals so that the immature and mature stages occur at any desired time, and obtaining hatched larvae from fertilized eggs laid by the individuals, wherein the rearing temperature for the individuals is maintained at 17 to 23°C from the first to fourth ovarian maturation in the rearing step. The preparation step may be the same as that of the embodiment of the maturation control method described above or the first embodiment.

[0078] One example of this embodiment includes a preparation step of preparing a population of crustaceans whose average weight has reached a weight at which they can lay eggs, and a rearing step of rearing the population of crustaceans so that the immature and mature stages occur at any time, and obtaining hatched larvae from the fertilized eggs spawned by the population of crustaceans, and the rearing temperature of the population of crustaceans may be maintained at 17 to 23°C from the first to fourth ovarian maturation in the rearing step. The preparation step may be similar to the content of the embodiment of the maturation control method described above or the first embodiment. By preparing the population of crustaceans, maturation can be adjusted as a whole at any frequency, resulting in a stable production of hatched larvae.

[0079] During the rearing process, the rearing temperature is maintained at 17-23°C, eliminating the need for significant temperature changes, which reduces utility costs associated with the use of temperature control equipment. For example, in relatively cool regions, crustacean hatched larvae can be obtained efficiently. Furthermore, a rearing temperature of 17-23°C can suppress the frequency of crustacean ovarian maturation, allowing for a stable supply of hatched larvae over a long period of time.

[0080] The rearing step may be the same as the rearing step of the first embodiment, except that the rearing temperature is maintained at 17 to 23° C. That is, in the rearing step, the crustaceans may be reared so that their ovaries repeatedly undergo immaturity and maturity.

[0081] When crustaceans are reared at a rearing temperature of 17 to 23°C for 15 days, the average ovarian maturation rate may be 1 to 5% / day, or even 2 to 4% / day. This prevents the crustacean ovaries from maturing too frequently. This sufficiently prevents deterioration of egg quality due to repeated ovarian maturation, allowing crustaceans to be reared over long periods of time and stably producing hatched larvae.

[0082] In the rearing step, the maturation interval of the ovaries of the Crustaceans may be 10 days or more, or 12 days or more on average. The ovarian maturation interval is calculated in the same manner as in the embodiment of the maturation control method described above. The ovarian maturation interval may be 13 days or more, or 14 days or more on average. By keeping the ovarian maturation interval within the above range, the ovarian maturation interval can be lengthened, and the frequency of ovarian maturation in Crustaceans can be suppressed. This allows the parent Crustaceans to be used for a long period of time, and improves the efficiency of obtaining hatched larvae. The ovarian maturation interval of the Crustaceans may be 20 days or less on average. An example of the ovarian maturation interval of the Crustaceans may be 10 to 20 days, or 12 to 20 days. The method for calculating the ovarian maturation interval and the average is the same as in the first embodiment.

[0083] From the same viewpoint as in the first embodiment, the number of days to maturity of the ovaries of Crustaceans may be 6 days or more, 7 days or more, or 8 days or more on average. The number of days to maturity of the ovaries of Crustaceans may be 10 days or less on average. An example of the number of days to maturity of the ovaries of Crustaceans may be 6 to 10 days. Furthermore, the number of days to immaturity of the ovaries of Crustaceans may be 5 days or more, 6 days or more, or 7 days or more on average. The number of days to immaturity of the ovaries of Crustaceans may be 10 days or less on average. An example of the number of days to immaturity of the ovaries of Crustaceans may be 5 to 10 days. The method for determining the number of days to maturity of the ovaries, the number of days to immaturity of the ovaries, and the average is as explained in the first embodiment.

[0084] In the rearing step, the number of rearing days may be a cumulative total of 90 days or more, 100 days or more, or 110 days or more. By keeping the number of rearing days within this range, the frequency of ovarian maturation of the Crustaceans can be further delayed. The number of rearing days in the rearing step may be a cumulative total of 200 days or less. An example of the number of rearing days may be a cumulative total of 90 to 200 days.

[0085] Other details regarding the rearing process can be directly applied to the above-described embodiment of the maturation control method or the first embodiment.

[0086] <Crustacean manufacturing method> A method for producing crustaceans according to one embodiment includes a culturing step of culturing hatched larvae obtained by the above-described method to obtain crustaceans. In the culturing step, the hatched larvae obtained by the above-described method are cultivated, so that crustaceans can be obtained stably. The obtained crustaceans may be used as individual crustaceans in the preparation step of the above-described method for producing crustacean hatched larvae.

[0087] <Crustaceans> In one embodiment, crustaceans are obtained by rearing one or more crustacean individuals that have reached a weight sufficient for egg production at a rearing temperature of 21°C or less for a cumulative total of 45 days or more. The number of rearing days at a temperature of 21°C or less may be a cumulative total of 60 days or more, 75 days or more, 90 days or more, 120 days or more, 150 days or more, or 180 days or more. The rearing temperature may be 20°C or less, 19°C or less, 18°C ​​or less, or 17°C or less. The rearing temperature may be any temperature that allows survival, but 15°C or higher is preferred because low temperatures can cause death. Because the obtained crustaceans can be maintained at temperatures lower than the appropriate rearing temperature, they may have low feeding activity and do not require large amounts of feed. The crustaceans obtained here can be maintained alive for long periods of time, and by raising the temperature at any time, the ovaries can be matured and hatched larvae can be produced.

[0088] In one example of this embodiment, a population of crustaceans whose average weight has reached the egg-laying weight is reared at a rearing temperature of 21°C or below for a cumulative total of 45 days or more to obtain crustaceans. The number of rearing days at a temperature of 21°C or below may be a cumulative total of 60 days or more, 75 days or more, 90 days or more, 120 days or more, 150 days or more, or 180 days or more. The rearing temperature may be 20°C or below, 19°C or below, 18°C ​​or below, or 17°C or below. The rearing temperature may be any temperature that allows survival, but 15°C or above is preferred because low temperatures can cause death. Because the obtained crustaceans can be maintained at temperatures lower than the appropriate rearing temperature, their feeding activity may be low and they may not require large amounts of feed. The obtained crustaceans can be maintained alive for long periods of time, and by raising the temperature at any time, the ovaries can be matured and hatched larvae can be produced. By adjusting the rearing temperature for the crustacean population, maturation can be adjusted at any frequency overall, resulting in stable egg production.

[0089] When the crustacean is vannamei shrimp, the amount of polyunsaturated fatty acids may be 238 mg or more, 250 mg or more, 300 mg or more, or 400 mg or more per gram of fatty acids. The amount of monounsaturated fatty acids may be 88 mg or more, 95 mg or more, 110 mg or more, or 120 mg or more per gram of fatty acids. The amount of saturated fatty acids may be 159 mg or less, 150 mg or less, 140 mg or less, or 130 mg or less per gram of fatty acids. When the crustacean is vannamei shrimp, the amount of total free amino acids may be 3500 mg or more, 3700 mg or more, 3900 mg or more, 4200 mg or more, or 4500 mg or more per 100 g of muscle. Because the crustacean is raised at a relatively low temperature, the amount of unsaturated fatty acids and free amino acids is increased.

[0090] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments.

[0091] The present disclosure includes the following embodiments. [1] A method for adjusting the maturation of ovaries of crustaceans, comprising a rearing step of adjusting the rearing temperature of one or more crustacean individuals to adjust the frequency of ovarian maturation. [2] The method for adjusting the maturation of the ovaries of a crustacean described in [1], wherein in the rearing step, the rearing temperature is adjusted so that the maturation interval of the ovaries of the crustacean individuals is 10 days or more on average. [3] The method for regulating maturation of Crustacean ovaries according to [1] or [2], wherein the rearing temperature is maintained at 20 to 24°C in the rearing step. [4] A method for regulating the maturation of Crustacean ovaries described in any one of [1] to [3], wherein in the rearing step, the Crustacean individuals are reared for a first period at an average temperature T1, and then for a second period at an average temperature T2 that is 2°C or more higher than the average temperature T1, thereby maturing the ovaries of the Crustacean individuals. [5] A method for adjusting the maturation of the ovaries of a crustacean described in [4], wherein the average maturation rate of the ovaries when the crustacean individuals are raised at the average temperature T2 is at least 1.5 times the average maturation rate of the ovaries when the crustacean individuals are raised at the average temperature T1. [6] A method for regulating maturation of crustacean ovaries according to [4] or [5], wherein the average temperature T1 is 19°C or lower and the average temperature T2 is 24°C or higher. [7] A method for regulating maturation of the ovaries of a crustacean according to any one of [1] to [6], wherein the rearing step is carried out by maturing the ovaries of the crustacean individuals without performing an eye stalk treatment. [8] The method for regulating maturation of Crustacean ovaries according to any one of [1] to [7], wherein the rearing period in the rearing step is a cumulative total of 90 days or more. [9] A method for regulating the maturation of the ovaries of a Crustacean described in any one of [1] to [8], wherein in the rearing step, the average number of hatched larvae per individual Crustacean obtained from the fertilized eggs of the Crustacean individuals during a cumulative period of up to 90 days from the start of rearing the Crustacean individuals is P1, and the average number of hatched larvae per individual Crustacean obtained from the fertilized eggs of the Crustacean individuals during a cumulative period of 91 to 180 days is P2, and P1≦P2.

[10] The method for regulating maturation of crustacean ovaries according to [9], wherein P2 / P1 is 1.5 or more.

[11] The method for regulating maturation of the ovaries of a crustacean according to any one of [1] to

[10] , wherein the crustacean includes a whiteleg shrimp.

[12] A method for regulating maturation of Crustacean ovaries according to any one of [1] to

[11] , which comprises a preparation step of preparing the Crustacean individuals weighing 30 g or more before the rearing step.

[13] a preparation step of preparing one or more crustacean individuals that have reached a spawning weight; and a rearing step of rearing the Crustacean individuals so that the immature stage and the mature stage are at any desired times, and obtaining hatched larvae from fertilized eggs laid by the Crustacean individuals, A method for producing hatched crustacean larvae, wherein the rearing step adjusts the rearing temperature of the crustacean individuals to adjust the frequency of ovarian maturation.

[14] The method for producing crustacean hatched larvae described in

[13] , wherein the rearing temperature is adjusted in the rearing step so that the ovarian maturation interval of the crustacean individuals is 10 days or more on average.

[15] The method for producing crustacean hatched larvae according to

[13] or

[14] , wherein the rearing temperature is maintained at 20 to 24°C in the rearing step.

[16] A method for producing crustacean hatched larvae described in any one of

[13] to

[15] , wherein in the rearing step, the crustacean individuals are reared for a first period at an average temperature T1, and then reared for a second period at an average temperature T2 that is 2°C or more higher than the average temperature T1, thereby maturing the ovaries of the crustacean individuals.

[17] A method for producing hatched crustacean larvae described in

[16] , wherein the average maturation rate of the ovaries when the crustacean individuals are reared at the average temperature T2 is at least 1.5 times the average maturation rate of the ovaries when the crustacean individuals are reared at the average temperature T1.

[18] The method for producing crustacean hatched larvae according to

[16] or

[17] , wherein the average temperature T1 is 19°C or lower and the average temperature T2 is 24°C or higher.

[19] A method for producing crustacean hatched larvae according to any one of

[13] to

[18] , wherein the rearing step involves maturing the ovaries of the crustacean individuals without performing an eye stalk treatment.

[20] The method for producing crustacean hatched larvae according to any one of

[13] to

[19] , wherein the rearing period in the rearing step is a cumulative total of 90 days or more.

[21] A method for producing crustacean hatched larvae according to any one of

[13] to

[20] , wherein in the rearing step, the average number of hatched larvae per individual crustacean obtained from the fertilized eggs of the crustacean individuals during a cumulative period of up to 90 days from the start of rearing the crustacean individuals is P1, and the average number of hatched larvae per individual crustacean obtained from the fertilized eggs of the crustacean individuals during a cumulative period of 91 to 180 days is P2, and P1≦P2.

[22] The method for producing crustacean hatched larvae according to

[21] , wherein P2 / P1 is 1.5 or more.

[23] a preparation step of preparing one or more crustacean individuals that have reached a spawning weight; and a rearing step of rearing the Crustacean individuals so that the immature stage and the mature stage are at any desired times, and obtaining hatched larvae from fertilized eggs laid by the Crustacean individuals, A method for producing hatched crustacean larvae, wherein the rearing temperature of the crustacean individuals is maintained at 17 to 23°C from the first to fourth ovarian maturation in the rearing step.

[24] The method for producing crustacean hatched larvae according to

[23] , wherein the rearing period in the rearing step is a cumulative 90 days or more.

[25] The method for producing crustacean hatched larvae according to any one of

[13] to

[24] , wherein the crustacean includes whiteleg shrimp.

[26] The method for producing crustacean hatched larvae according to any one of

[13] to

[25] , wherein the weight of the individual crustacean prepared in the preparation step is 30 g or more.

[27] A method for producing crustaceans, comprising a culturing step of culturing the hatched larvae obtained by the production method according to any one of

[13] to

[26] above to obtain crustaceans.

[28] Crustaceans obtained by rearing one or more crustacean individuals that have reached the spawning weight at a temperature of 21°C or less for a cumulative period of 45 days or more.

[29] The crustacean according to

[28] , wherein the crustacean is a whiteleg shrimp. [Example]

[0092] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to the following examples.

[0093] <Relationship between rearing temperature and ovarian maturity rate of whiteleg shrimp> Example 1 Nine vannamei shrimp that had reached a spawning weight (≥58 g) were reared in the first tank containing 5 tons of water at 27°C. After molting, they were transferred sequentially to the second tank containing 5 tons of water at 17°C. They were fed ad libitum with lugworms and commercially available kuruma shrimp feed. Starting with day 0, the day the first vannamei shrimp was transferred to the 17°C rearing water, the shrimp were reared in the second tank, with the water temperature adjusted to 17°C, for 15 days. The ovarian maturity of the vannamei shrimp in the second tank was visually determined, and the ovarian maturity rate was calculated every other day. The ovarian maturity of vannamei shrimp was determined by visual inspection: those with ovarian maturity stages I or II were considered immature, and those with ovarian maturity stages III or IV were considered mature. The maturation of the ovaries was determined at a fixed time of day. In the following examples, the maturation of the ovaries of the vannamei shrimp was determined in the same manner. The average maturation rate and standard deviation of the ovaries over 15 days after the start of rearing in the rearing water were calculated. The results are shown in Table 1.

[0094] Example 2 The individuals that had molted in the first tank were transferred one by one to the second tank containing rearing water at a temperature of 19°C, and rearing procedures were the same as in Example 1. The ovarian maturation rate was calculated every other day. Furthermore, the average ovarian maturation rate and standard deviation over 15 days were calculated. The results are shown in Table 1.

[0095] Example 3 The individuals that had molted in the first tank were transferred one by one to the second tank containing rearing water at a temperature of 21°C, and rearing was carried out in the same manner as in Example 1. The ovarian maturation rate was calculated every other day. Furthermore, the average ovarian maturation rate and standard deviation over 15 days were calculated. The results are shown in Table 1.

[0096] Example 4 The individuals that had molted in the first tank were transferred one by one to the second tank containing rearing water at a temperature of 23°C. The same procedures as in Example 1 were followed, and the ovarian maturation rate was calculated every other day. Furthermore, the average ovarian maturation rate and standard deviation over 15 days were calculated. The results are shown in Table 1.

[0097] Example 5 The individuals that had molted in the first tank were transferred one by one to the second tank containing rearing water at a temperature of 25°C, and rearing procedures were the same as in Example 1. The ovarian maturation rate was calculated every other day. Furthermore, the average ovarian maturation rate and standard deviation over 15 days were calculated. The results are shown in Table 1.

[0098] Example 6 The individuals that had molted in the first tank were transferred one by one to a second tank containing rearing water at a temperature of 27°C, and rearing was carried out in the same manner as in Example 1. The ovarian maturation rate was calculated every other day. Furthermore, the average ovarian maturation rate and standard deviation over 15 days were calculated. The results are shown in Table 1.

[0099] [Table 1]

[0100] As shown in Table 1, as the rearing temperature increased, the ovarian maturation rate of vannamei shrimp improved, and the average ovarian maturation rate over the first 15 days of rearing also increased. Furthermore, between water temperatures of 23°C, 25°C, and 27°C, the average ovarian maturation rate increased by more than 1.5 times for every 2°C increase in water temperature. Furthermore, at water temperatures of 17°C, 19°C, and 21°C, vannamei shrimp did not experience any ovarian maturation at all. Therefore, it was confirmed that a higher rearing temperature facilitates ovarian maturation and increases the frequency of ovarian maturation. It was also confirmed that raising the rearing temperature facilitates ovarian maturation over the entire rearing period and increases the frequency of ovarian maturation.

[0101] <Comparison of ovarian maturation intervals depending on rearing temperature> Example 7 Six vannamei shrimp, tagged with individual numbers for individual identification, were reared in aquaria at 23°C with 5 tonnes of water. They were fed a diet of lugworms and pelleted food ad libitum. From 0 to 16 days after rearing, the ovaries of each vannamei shrimp were visually inspected at 11:00 AM every day to determine whether they had matured. The results are shown in Figure 1.

[0102] Example 8 Whiteleg shrimp were reared in the same manner as in Example 7, except that the water temperature was set to 27° C., and whether the ovaries of each whiteleg shrimp were matured was determined visually in the same manner. The results are shown in FIG.

[0103] As shown in Figure 1, it was confirmed that the ovarian maturation period was longer in vannamei shrimp reared at a rearing temperature of 23°C than in those reared at a rearing temperature of 27°C. It was also confirmed that the ovarian immaturity period after spawning, until the ovaries mature again, was longer in vannamei shrimp reared at a rearing temperature of 23°C than in those reared at a rearing temperature of 27°C. The vannamei shrimp with the individual number "23°C-N3" in Figure 1 had a total of 12 days, including the period when the ovaries were not yet mature and the period when the ovaries were mature (ovarian maturation interval), which was longer than that of any of the vannamei shrimp reared at a rearing temperature of 27°C. Therefore, it is believed that by changing the rearing temperature from 27°C to 23°C, it is possible to lengthen the ovarian maturation period and ovarian maturation interval of vannamei shrimp, thereby enabling the stable production of hatched larvae over a long period of time.

[0104] Furthermore, the individual numbered "27°C-N5" in Figure 1 showed four ovarian maturation periods. Therefore, even when reared at 23°C, it is thought that ovarian maturation can be repeated at least four times by extending the rearing period.

[0105] <Effects of changing rearing temperature (1)> Example 9 Six 25-week-old whiteleg shrimp were prepared for experimental group A. Rearing of the six whiteleg shrimp began in rearing water at a temperature of 17°C. Forty-five days after the start of rearing (at 31 weeks of age), the water temperature was raised at a rate of 1°C / 12 hours. Rearing continued at a water temperature of 27°C until the shrimp reached 56 weeks of age. In experimental group A, the rearing period before the temperature increase was designated Period 1, and the rearing period after the temperature increase was designated Period 2. The average temperatures, T1 and T2, were 17°C and 27°C, respectively. The ovarian maturity rate was determined every week after the start of rearing. The results are shown in Table 2.

[0106] From the age of 31 weeks, the average individual weight and mating success rate were determined for any given week, and the average individual weight and mating success rate were calculated every three weeks. The mating success rate was determined by placing females with mature ovaries in a tank with males and visually confirming that the male had transferred spermatophore to the female. The mating success rate was calculated as the ratio of the number of fertilized females to the total number of females transferred to the male's tank. The results are shown in Table 3.

[0107] Example 10 For experimental group B, nine 25-week-old whiteleg shrimp were prepared and reared in rearing water at 17°C. Ninety days after the start of low-temperature rearing (at 38 weeks of age), the water temperature was raised at a rate of 1°C / 12 h. Rearing continued at 27°C until 56 weeks of age. Therefore, in experimental group B, the rearing period before the temperature increase was designated Period 1, and the rearing period after the temperature increase was designated Period 2. The average temperature T1 was 17°C, and the average temperature T2 was 27°C. The ovarian maturation rate was determined every week after the start of rearing. The results are shown in Table 2. The average individual body weight and mating success rate were measured using the same procedures as in experimental group A. The results are shown in Table 3.

[0108] Example 11 Thirty-two 25-week-old whiteleg shrimp were prepared as a group for experimental group C. They were reared in rearing water at a water temperature of 27°C using the same procedures as in Examples 9 and 10 until they reached 56 weeks of age, and the ovarian maturity rate was determined every week. Any shrimp that died during the rearing period were removed from the rearing water. The results are shown in Table 2. The average individual body weight and mating success rate were measured using the same procedures as in experimental group A. The results are shown in Table 3.

[0109] Furthermore, eggs laid at 33, 39, 42, 43, 46, 50, 52, and 55 weeks of age in each of experimental areas A, B, and C were collected, and the number of eggs laid per female (hereinafter referred to as "egg count") was calculated using an "XperCounter2 (trade name)" (manufactured by XpertSea). The eggs were then reared at a temperature of 29.0-29.5°C, and the number of hatched larvae per female was determined. The hatching rate per female in experimental areas A and B was calculated from the ratio of the total number of eggs to the total number of hatched larvae in experimental areas A and B. The hatching rate in experimental area C was calculated from the ratio of the total number of eggs laid to the total number of hatched larvae in experimental area C. The results are also shown in Table 3.

[0110] [Table 2]

[0111] As shown in Table 2, during the period when the rearing temperature was maintained at 17°C in Test Areas A and B, not a single vannamei shrimp underwent ovarian maturation. However, in both Test Areas A and B, when the water temperature was raised to 27°C after rearing at 17°C, the ovarian maturation rate increased, and was higher than that of Test Area C. On the other hand, in Test Area C, the ovaries matured earlier than in Test Areas A and B, which were reared at 17°C. Therefore, it was confirmed that ovarian maturation can be promoted by rearing vannamei shrimp at 17°C and then at 27°C. It was also confirmed that ovarian maturation can be promoted throughout the entire rearing period by rearing at 27°C after rearing at 17°C.

[0112] In experimental group C, the ovarian maturation rate decreased to below 40% after 40 weeks of age. On the other hand, in experimental groups A and B, there were weeks in which the ovarian maturation rate exceeded 40% even after 40 weeks of age. Therefore, it was confirmed that it is possible to mature the ovaries of vannamei shrimp over a long period of time by rearing them at a rearing temperature of 17°C to suppress ovarian maturation and then rearing them at a rearing temperature of 27°C.

[0113] [Table 3]

[0114] As shown in Table 3, at 31 weeks of age, the average individual body weights of both experimental groups A and B were smaller than those of experimental group C. However, after 31 weeks of age, the average individual body weights of experimental groups A and B increased, and the difference in average individual body weights at 55 to 57 weeks of age between experimental groups A and B and experimental group C narrowed. This indicates that vannamei shrimp can grow without problems even when reared at 17°C initially and then at 27°C. Comparing mating success rates, in experimental group C, the mating success rate decreased after 49 weeks of age, reaching 33% at 52 to 54 weeks of age. In contrast, in experimental group A, the mating success rate remained high at 63% even between 55 and 57 weeks of age. Therefore, mating of vannamei shrimp was possible for a longer period in experimental groups A and B than in experimental group C.

[0115] Comparing the hatching rate and number of hatched larvae, the hatching rate in Test Area C was 0% at 52 weeks of age. On the other hand, in Test Areas A and B, the hatching rate was 59.4% and the number of hatched larvae was 393,500 even at 55 weeks of age. Therefore, it was confirmed that in Test Areas A and B, the egg quality did not deteriorate even after long-term rearing, and hatched larvae could be obtained stably. It was also confirmed that hatched larvae could be obtained stably throughout the entire rearing period.

[0116] <Effects of changing rearing temperature (2)> Example 12 Six 25-week-old whiteleg shrimp were prepared as a group for experimental group D. Rearing of the six whiteleg shrimp was initiated in rearing water at a temperature of 23°C. 90 days after the start of rearing, the water temperature was raised at a rate of 1°C / 12h to 27°C, and rearing was continued for 90 days. Therefore, in experimental group D, the rearing period before the temperature increase was designated Period 1, and the rearing period after the temperature increase was designated Period 2, with the average temperature T1 being 23°C and the average temperature T2 being 27°C.

[0117] After the start of rearing, the ovaries of the vannamei shrimp were visually inspected daily for maturity. If the ovaries of the vannamei shrimp were mature, females with mature ovaries were placed in the male's tank for mating. The eggs were collected and the number of eggs laid per female was calculated using an XperCounter2 (product name) (manufactured by XpertSea). The eggs were then reared at a temperature of 29.0-29.5°C, and the number of hatched larvae per female was counted. The hatching rate per female was calculated from the total number of eggs laid and the number of hatched larvae. The average number of eggs laid per female, the average number of hatched larvae, and the average hatching rate were calculated from days 1 to 90 of rearing. The average number of eggs laid per female, the average number of hatched larvae, and the average hatching rate were also calculated from days 91 to 180 of rearing. The results are shown in Table 4.

[0118] Example 13 Six 25-week-old whiteleg shrimp were prepared as a group for experimental group E. The whiteleg shrimp were reared in the same manner as in Example 12, except that the rearing water temperature was set to 27°C. The number of eggs laid per female, the number of hatched larvae, and the hatching rate were calculated. The average number of eggs laid per female, the average number of hatched larvae, and the average hatching rate were also calculated for days 1 to 90 after rearing, and the average number of eggs laid per female, the average number of hatched larvae, and the average hatching rate for days 91 to 180 after rearing. The results are shown in Table 4.

[0119] [Table 4]

[0120] As shown in Table 4, in experimental area E, where the rearing temperature was 27°C, the average number of hatched larvae from 91 to 180 days after rearing was lower than the average number of hatched larvae from 1 to 90 days after rearing. On the other hand, in experimental area D, the average number of hatched larvae from 91 to 180 days after rearing was higher than the average number of hatched larvae from 1 to 90 days after rearing. Therefore, it was confirmed that rearing whiteleg shrimp, whose ovarian maturation had been temporarily suppressed at a rearing temperature of 23°C, at a rearing temperature of 27°C could promote ovarian maturation and enable the stable production of hatched larvae. These results demonstrate that rearing at a low temperature followed by rearing at an appropriate temperature can produce hatched larvae over a long period of time. Furthermore, it was demonstrated that rearing at a low temperature followed by rearing at an appropriate temperature can produce hatched larvae over a long period of time. [Industrial Applicability]

[0121] The present disclosure can provide a method for adjusting the maturation of Crustacean ovaries, a method for producing Crustacean hatched larvae, and Crustaceans, which enable stable production of hatched larvae. The present disclosure can also provide a method for producing Crustaceans, which enables stable production of Crustaceans by culturing such hatched larvae.

Claims

1. The whiteleg shrimp is obtained by rearing one or more whiteleg shrimp that have reached a weight suitable for spawning at a rearing temperature of 21 to 23°C for a total of 90 days or more.

2. The whiteleg shrimp is obtained by rearing one or more whiteleg shrimp individuals that have reached a weight capable of spawning in a first period in which the average temperature T1 is 19°C or less, and then rearing them in a second period in which the average temperature T2 is 27°C or more.

3. 3. The whiteleg shrimp of claim 2, wherein the first period is 70 days or more.

4. The vannamei shrimp according to any one of claims 1 to 3, containing 238 mg or more of polyunsaturated fatty acids per 1 g of fatty acids.

5. The vannamei shrimp according to any one of claims 1 to 3, containing 88 mg or more of monounsaturated fatty acids per 1 g of fatty acids.

6. The vannamei shrimp according to any one of claims 1 to 3, containing 159 mg or less of saturated fatty acids per 1 g of fatty acids.

7. The vannamei shrimp according to any one of claims 1 to 3, containing 3500 mg or more of total free amino acids per 100 g of muscle.

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