What to pay attention to when stocking fish fry in reservoirs in winter

Every winter is the golden season for stocking fish species such as silver carp, bighead carp, grass carp, and black carp into reservoirs. But quite a few @#@233@#@ households report that within 2 to 7 days after stocking the fry, large numbers of dead fish and swimming sick fish appear on the surface of the reservoir water; these fish lose their luster and their body surface mucus increases. Based on the above symptoms, it can be inferred that the fish have contracted a typical case of "acclimation sickness." This disease is mainly caused by a drastic change in water temperature, in which the nerve endings in the fish skin are strongly stimulated, causing dysfunction of the internal organs; its mortality rate is as high as 20%-60%, causing severe economic losses to fishermen. So, how can this disease be prevented?

1. Adjust the temperature difference. Set up net cages in advance in the reservoir's bay. When the water temperature of the fry pond differs from the reservoir water temperature by more than 3°C, the temperature difference should first be gradually adjusted, and only after the fry have adapted to the reservoir's water environment should they be put into the reservoir. The method is to gradually add reservoir water to the tank holding the fry; when the water temperature in the tank holding the fry approaches the reservoir water temperature, wait another 10 to 30 minutes, then slowly pour the fry together with the water into the net cage, letting the fry adapt to the new water environment; after holding them temporarily in the net cage for 120 minutes, the fry can be allowed to swim freely into the reservoir.

2. Drug prevention. Since reservoir water temperature is often lower than the water temperature of the fry pond, the method of combining garlic juice with urea can be used to prevent "acclimation sickness" in fry; it has very good results and no side effects whatsoever on the fry. Add 1.3 kg of garlic pulp juice to every 500 kg of water. After the fry are loaded into the tank, wrap 2.5 kg of urea in cotton cloth for every 500 kg of water and let it sink to the bottom of the tank. As the urea slowly dissolves, it absorbs the heat of the water body in the tank, causing the water temperature in the fry transport tank to slowly decrease, which helps the fry adapt to a lower water temperature environment.