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Artificial breeding of fry
First, artificial breeding of fry
1. Selecting broodstock: Choose 3rd to 5th instar fish weighing between 2.5kg and 3.5kg. During the non-reproductive season, males and females can be distinguished by their head shape and coloration—males have slightly broader heads, darker bodies, while females have narrower heads. During the reproductive season, males develop noticeable muscle tumors on both sides of their heads, and their gonads show papillae. The abdomen becomes stiff and hard to bend, while females have a soft, swollen belly with a round, concave genital opening, appearing pale gray. The male-to-female ratio should be maintained at 3:2 for optimal breeding results.
2. Broodstock cultivation pond: The pond area is approximately 2500m² with a water depth of about 1.5m. The stocking density is 20–30 per 667m². When the water temperature exceeds 13°C, special feed is introduced. Once the temperature reaches 21°C or higher, the feeding rate should be between 2% and 4%. Supplement the diet with small amounts of animal-based food such as boiled fish or shrimp, along with plant-based materials like malt. Rinse the broodstock every 10 days to stimulate gonad development and improve spawning success.
3. Artificial hormone application: Commonly used hormones include carp pituitary (PG), human chorionic gonadotropin (HCG), and luteinizing hormone-releasing hormone (LRH-A) and its analogues. For each kilogram of female fish, administer 4–6mg of PG, 1000 international units of HCG, or 2–2.5mg of LRH-A. A combination of PG and HCG can also be used at a dosage of 2mg PG plus 600–700 international units of HCG. Males receive half the dose of the females.
4. Setting up spawning nests: Use plastic buckets, iron buckets, or wooden boxes that can accommodate one pair of broodstock. One end of the nest should be open for the fish to enter and exit, while the other end is covered with a nylon cloth. After spawning, place the nests on the bottom of the pond, 3–5 meters deep, with a water depth of 0.5–1 meter. Ensure the opening faces the center of the pond and attach a float for easy positioning. Maintain a spacing of 9–10 meters between nests, and use about 50% of the total broodstock in this setup.
5. Egg collection: When the water temperature is above 21°C, check the nests daily between 10am and 11am. Gently drive the broodstock away if they are present. If eggs are found, carefully remove them and place them into a smooth barrel filled with pond water. This helps protect the eggs from predation and environmental stress.
6. Egg hatching and larval development: Fertilized eggs hatch within 110–120 hours when the water temperature is between 25°C and 29°C. It takes approximately 10 days for larvae to develop into juveniles. Eggs can be naturally hatched in ponds or in hatching tanks. The ideal incubation conditions include a water temperature of 25°C–28°C, a pH range of 6.5–8.0, and dissolved oxygen levels of at least 6 mg/L. Water exchange should be around 20 liters per minute.
7. Preventing fungal infections: To prevent water mold, alternate between mildewin and formalin treatments. Apply the treatment once daily before the eggs turn red. Soak the eggs in a solution of water mold net at 60–65mg/L for 10–12 minutes, or immerse them in 100mg/L formalin for 4–10 minutes. These steps help reduce the risk of fungal infections and increase survival rates.