The selection of pro-shellfish typically involves individuals larger than 4 cm in size. For those over 4 cm from various sources, special attention should be given to sampling for cell maturity testing. When the gonads are fully developed, the egg cells appear spherical, and spermatozoa become more active. These can be considered as suitable pro-shellfish, while underdeveloped ones cannot. After mature oysters are stimulated and spawn, a large quantity of eggs and sperm is released. However, if the sexual maturation is poor, no matter what induction methods are used, they fail to reach peak spawning, resulting in small, low-quality eggs with high rates of abnormal development.
The method of inducing spawning begins with dry stimulation using probiotics and seawater, followed by immersion in 0.15–0.25% ammonia solution, then placing the shellfish in a warmed spawning tank at around 28°C. Pro-shellfish placed in holding tanks may spawn naturally without artificial intervention. Spawning usually occurs during midnight or early morning. During this time, males release milky white sperm in a cloud-like manner through the outlet pipe, while females expel light-yellow eggs or fragments that settle at the bottom. The spawning process can last several hours.
To obtain pure sperm and eggs, male and female parents should be separated and spawned in different containers. The collected gametes are then filtered through a sieve to remove impurities and excess sperm for fertilization. Scallops are monospermic, meaning only one sperm is needed to fertilize an egg. Too many sperm can lead to abnormalities. Typically, a few actively swimming sperm surround each egg to avoid over-fertilization and deformed embryos. After fertilization, the eggs must be washed multiple times to remove any unfertilized eggs and excess sperm that settle slowly. This ensures optimal water conditions for embryo development, after which the siphon method is used to concentrate the culture. The density should be between several to ten per milliliter of water, avoiding excessive crowding.
It is essential to prevent harmful algae and protozoa from entering the culture tank. The culture water must be settled using black worms and strictly filtered before use. The specific gravity of the culture water should range from 1.010 to 1.025, with the ideal range being 1.015 to 1.025. The lower limit should not drop below 1.005, and the upper limit should not exceed 1.030.
Larvae are relatively large, with shell lengths generally exceeding 119 microns. Their feeding requirements are not overly strict, but during the high-temperature season, the bait must be carefully managed to prevent water pollution. It is beneficial to use artificially cultivated, heat-resistant microalgae as food.
When larvae transition to benthic life, it is crucial to introduce the substrate at the right time. This timing depends on the natural behavior of the larvae. As they enter the metamorphosis stage, they become highly active, crawling and extending their foot-like structures frequently, indicating their need for a suitable substrate. The sand used should be fine (not exceeding 150 microns) and thoroughly disinfected. The substrate layer should be about 0.5 cm thick, not exceeding 1 cm. When transitioning to benthic seedlings, they secrete a lot of mucus, often entangling themselves and affecting their survival. To prevent this, regular water exchange and external stirring should be performed, along with careful monitoring of water quality.
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