Intensive cultivation techniques of parent fish during transformation period

With the increase of water temperature after spring, gonad development of parent fish gradually transformed. Especially from spring to mid-May before parturition, the gonad transformation of parent fish is very fast, and the ovarian coefficient can reach 15%~20%. During this period, intensive cultivation and management of parent fish during transformation period can promote smooth spawning; otherwise, gonad development will stagnate or even degenerate. The intensive culture techniques for parent fish transformation are as follows.

1. Divide the pool at the right time. In order to master the growth and development of parent fish and facilitate the arrangement of spawning and reproduction, it is advisable to divide parent fish into pools at 10℃. Disinfect the small pond before pool division, and transfer the parent fish cultivated in the larger pond during winter to the small pond with 667~1330 square meters (1~2 mu) water surface for cultivation. The parent fish with good growth and development and the parent fish with poor growth and development are separately bred, and the density is 120 kg to 150 kg per 667 square meters of water surface. Parental fish released in the same pond should complete spawning at one time. In this way, it is not only convenient to strengthen the prenatal cultivation of those parent fish with poor growth and development, but also to avoid disturbing other parent fish that have not yet spawned when spawning to catch parent fish. The brood fish with injuries were treated with medicine when the pool was divided.

2. Reasonable feeding. After spring, parent fish need a lot of nutrients for gonad development. The parent fish ponds of silver carp and bighead carp should apply more manure, and organic fertilizer 300 kg ~500 kg should be applied per 667 square meters. The amount of topdressing is less and more, so that the pool water is both "alive" and "fertile." Apply less or stop fertilization 15 days before spawning. Grass and green parent fish were fed mainly with green feed, supplemented with concentrate feed. Feed grain sprout, malt, bran cake, etc. in the early stage, and feed lettuce leaves, ryegrass and other green materials as early as possible. Near the spawning stage, the food intake of mature herbage parent fish decreased obviously, even stopped eating. Green parent fish are fed mainly with snail and clam meat, supplemented by bean cake and compound feed.

3. Scientific management of water. After spring, the pond depth should be 1 meter, which is conducive to the recovery of water temperature and the promotion of food organism reproduction. The parent fish pond should be flushed with new water frequently to keep the water fresh. Silver carp and bighead carp brood ponds flush once every 10 days, grass and green brood ponds flush once a week. After that, the interval between middle water was gradually shortened. Half a month before delivery, silver carp and bighead carp brood ponds were flushed every other day, grass and green brood ponds were flushed every day. Flushing new water should be carried out in the afternoon, each flushing 3~5 hours, so that the depth of the pool water increased by 15~20 cm. The brood pond is sprinkled with secondary lime water every one week, and the dosage is 10 kg ~15 kg per 667 square meters. Regulate the pH of the pool water in time and keep the pH value at 7~8.5 to promote the development of fish eggs.

4. Prevention of diseases. To prevent bacterial fish disease in brood pond, 1g bleaching powder, 5g disinfectant, 25g quicklime and 0.3g strong chlorine are used in each cubic meter of water. To prevent parasitic fish diseases, 0.8 g trichlorfon, 0.5 g copper sulfate and 0.6 g strong chlorhexidine were sprayed on each cubic meter of water, or 0.5 g copper sulfate and 0.2 g ferrous sulfate were mixed with 200 kg water, and the whole pool was sprayed once every half month.