In general, the grouper is a hermaphrodite, and as the individual grows, it undergoes sexual conversion. The first is to become a female and continue to grow and become a male. Before the gonads are immature, it is not easy to distinguish between male and female. The sexually transformed individuals vary by species, age, and size. Groupers start spawning from March each year, and the females have many characteristics of spawning. The egg is spherical, colorless and transparent. There is an oil ball in the egg, which is a floating egg. When the water temperature is between 25°C and 27°C, it hatches after about 23 hours to 25 hours. The unfertilized eggs sink to the bottom of the sea.
In order to solve the seedlings of groupers, many marine biologists at home and abroad have conducted many experimental researches on artificial reproduction techniques and made great progress. The main reason is to use oral production products to accelerate the sexual transformation of mature females and greatly shorten the natural The time needed for sexual conversion. China Marine Fisheries Research Institute of Zhejiang Province (1980) and Zhoushan District Fisheries Research Institute (1981) succeeded in artificial insemination and hatching of blue grouper, and the South China Sea Fisheries Research Institute also made breakthroughs in the artificial breeding of grouper.
Before the technology for artificial propagation of grouper seedlings has yet to solve the production needs, the cultured seedlings must rely on natural harvesting, that is, catching small fish (small catches when commercial fish are sold, small stockpiles or when seedlings sell). Now, with the rapid development of the grouper fish breeding industry, the natural seeds have been in short supply. Artificial breeding of grouper has attracted widespread attention in recent years. In the following, red-spotted groupers are used as examples to introduce artificial seedling raising techniques.
Broodstock selection and breeding: broodstock can be artificially propagated or caught in natural sea areas. Females choose to weigh 0.5 kg to 1 kg, the abdomen is enlarged and soft; males choose to weigh more than 1.5 kilograms and gently press the abdomen to ejaculate. Male and female broodstock with a ratio of 1:1 to 1:3. Grouper is a female prehybrid hermaphrodite fish, and its 6th instar was transformed into a male fish. In recent years, due to overfishing, the sex ratio of polyandroidism is less in the reproductive groups of natural sea areas, and it is cultivated under cultivation conditions. Older male individuals have long broodstock and are expensive. Therefore, the problem with broodstock selection is that it is not easy for males to get mature gonads.
In order to solve the problem of male broodstock deficiency in artificial reproduction, exogenous sex hormones can be used to induce the hermaphrodite red-spotted groupers to change their females into reproductive male broodstock as early as 3rd to 4th instar. For 50 days of baits for 2nd to 4th instar fish, the fertility of sexually transformed male broodstock was 93.5%, fertilization rate was 81.1%, and embryonic development was normal.
In order to solve the relatively rare problem of artificially breeding neutral males, cryopreservation can also be used to preserve the semen. After 2 months of cryopreservation in liquid nitrogen tanks, the semen still has the vitality equivalent to fresh essence without affecting artificial reproduction. Effect. The effect of artificial reproduction largely depends on the maturity of the gonad gonads, so it is important to strengthen broodstock development and promote gonad development before inducing spawning. Reserve or hold grouper broodstock in the indoor concrete pool, artificially strengthen the cultivation, change the water and suck the dirt daily, the broodstock can spawn and fertilize naturally without hormone production, and can obtain high-quality fertilized eggs.
Artificial insemination of red-spotted groupers should adopt dry insemination. The broodstock can be spawned 10 to 13 hours after the injection of the second oxytocic agent. The abdomen of the female fish is gently pressed from top to bottom, and the mature fish eggs are squeezed into the disinfected white porcelain bowl, and repeated 5 to 6 times. The broodstock can be gently returned to the broodstock tank. Immediately thereafter, the male semen was squeezed into the egg pile of a white porcelain bowl in the same manner. Grouper semen is rare. Even if it is squeezed 5 or 6 times in total, it is only 1 ml to 2 ml. After the final squeeze is completed, the eggs and semen in the bowl are stirred with clean feathers soaked in sterile seawater. After 1 minute to 2 minutes, add a small amount of disinfected seawater, continue stirring for 5 minutes, and pour it into a small sterilized basin. Stir with sterile seawater and let stand for a while. All fertilized eggs float in the upper and middle layers of water, and dead eggs or unfertilized eggs precipitate at the bottom. Wash the fertilized eggs with sterile seawater, remove excess sperm to avoid multiple sperm fertilization, and then transfer the fertilized eggs to the incubator.
When artificial insemination, direct sunlight should be avoided to avoid killing sperm. As the grouper spawns fish spawned in batches, there are several reproductive characteristics of spawning. If the broodstock creates environmental conditions for natural spawning and fertilization in the spawning pool, it is possible to avoid the disadvantages of over-ripening or under-ripening of eggs that often occur during artificial insemination, and also to reduce the risk of brooding, squeezing eggs, and semen. Damage from broodstock. Natural spawning is better than artificial insemination. Suitable spawning water temperature 25 °C ~ 27 °C, sea water salinity 32 ~ 35, pH7.8 ~ 8.5, water depth of about 1.5 meters, shade above the pool shading, water flow 40 liters / min ~ 50 liters / min.
Groupers produce buoyant eggs and hatching should be done in a ring incubator or hatching tank. The egg density during hatching ranges from 50 eggs/liter seawater to 100 eggs/liter seawater, and the water velocity is such that the eggs or larvae float. The hatchery water must be fresh and must be sterilized by sand filtration and ultraviolet light. The water temperature is maintained at about 25°C, and the salinity is 30% to 33%, and it is stable. During the incubation, remove dead eggs as much as possible to make the waterproof material worse. Red-spotted grouper and blue grouper eggs In the above conditions, fry can be hatched after 24 hours from fertilization. Http://Content/5c7246c7-0c67-4e37-beda-26cd887bdfab?cType=2
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