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 the sperm exhibit more active movement. These can be used as pro-shellfish, while underdeveloped ones cannot. Once mature oysters are stimulated and spawn, a large quantity of eggs and sperm are released. Progenitors with poor sexual maturation, regardless of the induction methods applied, fail to reach peak spawning, resulting in small, low-quality eggs and abnormal hatching rates.
The method of stimulating spawning begins with dry stimulation using probiotics and seawater, followed by immersion in 0.15–0.25% ammonia water. The oysters are then placed in a spawning tank filled with warm water, gradually heated to 28°C. Some pro-shellfish may naturally release gametes without artificial intervention. Spawning typically occurs during the night or early morning. During this time, males release milky-white sperm in cloud-like bursts 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 progenitors should be separated and allowed to spawn in different containers. After collection, the gametes are filtered through a sieve to remove impurities and excess semen for fertilization. Scallops are monospermic, so it's important not to use too much sperm. Usually, a few active sperm surround each egg to avoid over-fertilization and deformed embryos. Following fertilization, the eggs must be washed multiple times to remove any immature eggs and excess sperm that settle slowly. This ensures optimal conditions for embryonic development, after which the siphon method is used to concentrate the culture. The density should be around several per milliliter of water, ideally not exceeding ten per milliliter to prevent overcrowding.
It is crucial to prevent harmful algae and protozoa from entering the culture tank. The culture water must be filtered through black worms and thoroughly cleaned before use. The specific gravity of the water should range between 1.010 and 1.025, with an ideal range of 1.015–1.025. The lower limit should not go below 1.005, and the upper limit should not exceed 1.030.
Larvae are relatively large, with shell lengths generally over 119 microns. Their feeding requirements are not overly strict, but since nursery work is often conducted during high temperatures, the bait must be carefully managed to prevent water pollution. It is beneficial to use artificially cultivated, heat-resistant microalgae as feed.
When larvae transition to benthic life, it is essential to introduce the substrate at the right time. The timing is based on larval behavior. Larvae entering the metamorphosis stage become highly active, crawling and extending their foot-like structures frequently. They perform continuous soil-like movements, indicating their need for a suitable substrate. The sand should be fine (not exceeding 150 μm) and strictly disinfected. The substrate thickness should be controlled at 0.5 cm, not more than 1 cm. As they transition to benthic seedlings, they secrete a lot of mucus, which can entangle them, affecting their survival. To prevent this, increased water exchange and external stirring should be performed. Additionally, maintaining clean and stable water conditions is critical for their healthy development.
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