Key Technical Points for Spring Intensive Conditioning of Broodstock

Spring is a critical period for gonadal growth in broodstock. Whether broodstock are conditioned well or poorly at this stage directly affects the success or failure of artificial propagation of Chinese carp, so on the basis of routine conditioning, spring conditioning must be given special attention.

1. Adjust the water level of the broodstock pond and raise the water temperature. On sunny days, drain water promptly to lower the pond water level and speed up the rise in water temperature. The amount drained can be about 30 cm of water level reduction. When rainy days or cold air arrive, fill the pond in advance to slow the loss of heat from the pond water.

2. Strengthen feeding management and provide sufficient, high-quality feed and fertilizer. Spring is the stage of gonadal development in fish, and feed intake increases. For black carp broodstock ponds, mainly provide sufficient fresh and live animal-based feed with high protein content, such as river snails, small clams, and mussel meat; the daily feeding amount can account for 3%-5% of fish body weight, supplemented with soybean cake and commercial concentrated feed such as compound pellet feed. For grass carp broodstock ponds, mainly feed fresh tender green feed, with a daily feeding amount of 40 kg-60 kg per mu, supplemented with high-protein feeds such as barley malt and soybean cake. For silver carp and bighead carp broodstock ponds, mainly strengthen fertilization, which can be applied once every 2 days-3 days, about 60 kg of manure each time, supplemented with powdered compound feed or soybean cake slurry. When the water temperature rises above 20°C, attention should be paid to gradually reducing and finally stopping concentrated feed to prevent excessive fat accumulation in broodstock, which can delay gonadal maturation and cause difficult spawning.

3. Strengthen water quality management and provide flowing-water stimulation. Keep the water quality fertile, lively, tender, and brisk. For black carp and grass carp broodstock ponds, maintain transparency above 35 cm. Pay attention to frequent water addition, 2 times-3 times per month, 20 cm-30 cm each time. For silver carp and bighead carp broodstock ponds, maintain transparency at about 30 cm, with water addition 3 times-4 times per month, 10 cm-20 cm each time. From late April, enter the pre-spawning flowing-water stimulation stage, once daily, 2 hours-4 hours each time.

4. Actively prevent and treat fish diseases to reduce broodstock losses. The main diseases of broodstock include print disease, red-skin disease, and Lernaea disease. Prevention and treatment methods include: (1) 1 ppm bleaching powder or 2 ppm-4 ppm Chinese gallnut, splashed over the whole pond to prevent print disease and red-skin disease. (2) To treat red-skin disease, inject chlortetracycline or chloramphenicol at 5 mg per kg of diseased fish body weight, and apply 1% carbolic acid to the affected area. (3) To treat print disease, wash the affected area with 1% benzoic acid. (4) For Lernaea disease, splash 0.2 ppm-0.5 ppm 90% crystallized trichlorfon over the whole pond to kill the parasites, which has a good prevention and treatment effect.