Technical Measures to Reduce the Mortality Rate of Induced Spawning Broodfish

Reducing the death of induced spawning broodfish is an important technical task in fry aquaculture. There are two main factors causing the death of induced spawning broodfish. First, broodfish consume a great deal of physical energy during the spawning and reproduction process, which increases the side effects of the inducing drugs and lowers the body's resistance. If the fish is severely injured, various pathogens will take the opportunity to infect the fish body, causing disease and leading to the death of the broodfish. Second, the broodfish has a poor physique, or the water temperature fluctuates greatly during induction, or the dosage of the inducing drugs is improper (too high or too low), so the broodfish cannot spawn normally or experiences difficult spawning, and this in turn causes its own physiological activities to become disordered and leads to death. Therefore, emphasis must be placed on pre-spawning cultivation and post-spawning care of the broodfish. In addition to the pre-spawning cultivation work that must be done well so that the broodfish have a strong physique, attention must first be paid to fishing operations, which is an important link in reducing broodfish injuries and deaths. Whether pulling and catching broodfish in the broodfish pond or in the spawning pond, the netting action must be quick and coordinated. As soon as the net panel approaches the bank, the net should be quickly closed. After the net panel is properly laid and covered, the broodfish in the net should quickly be moved away from the pond wall to avoid the broodfish colliding with the pond wall and being injured. On sunny days when the temperature is relatively high and the fish transport distance (the distance between the broodfish pond and the spawning pond) is relatively long, it is best to catch fish in the early morning or in the evening to prevent the broodfish from being injured by oxygen deprivation and suffocation inside the canvas stretcher. Broodfish with a relatively good physique and appropriate gonadal maturity should be selected for induced spawning, and drugs should not be used at high doses for induction. Second, when pulling and catching the broodfish after induced spawning from the spawning pond, they should be checked one by one. For female broodfish with an enlarged abdomen, the abdomen should be gently pressed by hand to help them release the mature eggs already in the abdomen. If the broodfish has difficult spawning because the genital pore is blocked, a sterilized scalpel or scissors should be used to cut and enlarge the blocked genital pore so that the mature fish eggs can be discharged from the body. This can prevent the mature fish eggs from absorbing water and swelling inside the broodfish and endangering the broodfish (this is the main cause of death of female broodfish). For broodfish with wounds on the body surface, first wipe the wound dry with absorbent cotton, then apply and wash with potassium permanganate solution or malachite green solution containing 1% table salt, then use a finger to apply iodine tincture (iodine tincture) to the wound from the tail toward the head against the direction of the scales, and then apply ointment. Broodfish after induced spawning, whether injured or not, should be injected with an appropriate dose of anti-inflammatory and disease-resistant drugs according to body weight. The pond where post-spawning broodfish are stocked must first be cleared and disinfected with quicklime. The pond water should be fresh, and a water depth of about 1.5 m is suitable. During the first month after the post-spawning broodfish are put into the pond, it is best not to apply organic fertilizer, and drugs such as bleaching powder, strong chlorine essence, or fish and shrimp safety preparation should be used regularly to disinfect and sterilize and to prevent and treat fish diseases. About 5 days after the broodfish are put into the pond, feeding begins, mainly feeding grain sprouts, malt, bran cake, or compound feed that the broodfish like to eat. For grass carp broodfish, an appropriate amount of fresh tender green grass should be fed. Generally, a small amount of fresh water is replaced every 3 to 5 days to regulate the water quality in the pond, stimulate the appetite of the broodfish, enable them to recover quickly, and enhance disease resistance.