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Fish breeding seedlings
In order to quickly restore post-disaster aquaculture production and compensate for the shortage of fish seedlings, it is feasible to utilize autumn fish fry to raise species that will later be cultured into adults. The following are the key technical steps:
First, broodstock cultivation. Once the floodwaters recede, it is crucial to clean and disinfect the ponds promptly, then separate and rear the broodstock. Apply base fertilizers and feed them with green feed, supplemented with concentrated feed as needed. During this period, water quality must be strictly controlled and feeding should be done carefully to promote gonad development.
Second, pre-breeding preparation. Autumn fish species require higher temperatures and more complex techniques. All preparations must be thorough. The entire breeding process should be well planned—checking gonad development, inspecting equipment, selecting cool weather, and assigning experienced personnel. If possible, use deep well water to regulate temperature.
Third, hormone-induced spawning. For grass carp, use luteinizing hormone-releasing hormone analogues (LRH-A), while for eels and other species, human chorionic gonadotropin (HCG) or a mix of types A and B can be used. After injection, keep the environment quiet. Maintain a gentle water flow in the spawning pool. Begin flushing stimulation 2–4 hours before spawning and check the spawning nets every 6–10 hours. If eggs appear outside the body, artificial insemination can proceed. Post-spawning broodstock should be treated with chlortetracycline ointment and given antibiotics or health care agents.
Fourth, hatching management. The incubation water must be clean and free from pollution, filtered through 40–50 mesh screens. Dissolved oxygen should remain above 4 mg/L, with a pH between 7 and 8. Place about 200,000 fertilized eggs in a 200 kg incubator tank. Maintain a "high-low-high-low" flow rate to ensure even egg movement. If large zooplankton like water fleas are present, treat the water with trichlorfon at 0.2–0.5 g per cubic meter. Treat prematurely ruptured eggs with potassium permanganate solution.
Fifth, fry transportation. Fry can be transported when their yolk sacs have nearly disappeared and they can start feeding. Use oxygenated nylon bags (30–70 cm in size), each containing around 50,000 fry. Avoid direct sunlight and high temperatures, and ensure the temperature difference between the incubator, transport bag, and pond does not exceed 3°C.
Sixth, fry rearing. Before stocking, clean and disinfect the rearing ponds, apply sufficient base fertilizer, and cultivate natural food sources. Stock 30,000–50,000 fry per acre. Initially raise them in cages and feed with boiled egg yolk. Keep the water thin by feeding 3 kg of soybean pulp per acre, 3–4 times daily, and regularly replace the water to prevent floating heads. After about 10 days, when the fry reach 2 cm, perform several net exercises before moving them to separate ponds.
Seventh, fingerling feeding. After passing through early-stage ponds, the fish can grow to about 10 cm. Stock 3,000–5,000 fish per acre, depending on the species and traditional polyculture ratios. Ponds with grasses and aquatic plants should be fed with duckweed or tender grasses. Ponds with carnivorous species should receive organic and chemical fertilizers, along with bean cakes, cottonseed cakes, and other commercial feeds to accelerate growth.