In the hatching process of fish fry, the phenomena of early release and malformation of embryo occur occasionally, which seriously affects the emergence rate. Early release occurs mostly during the period from the emergence of the caudal fin to the muscle-effect period of the embryonic development. The egg membrane ruptures or dissolves, and the embryo body that lost the protection of the egg membrane sinks to the bottom of the water and dies. Occurrence of the reasons: First, the poor quality of fish eggs, or over-cooked eggs, egg membrane is crisp and poor flexibility, easily damaged; Second, the hatching tank wall is rough, easy to roll with the water floating eggs eggs are being scratched Third, the ovulation density is too large, or the quality of the hatchery water is poor, and the pH is low or high. Fourth, several hatching ponds use recycled water at the same time, and each hatching pond has different time to enter the egg. The eggs hatched in the hatchery pool are released as early as possible, and the egg-bound enzyme released into the water enters the hatching pool of the fish eggs along with the circulating water, causing the fish eggs hatched in the rear hatch pool to be released in advance. What preventive measures should be taken?

1. The rough wall of the hatching tank must be smoothed with a grinding wheel; the proper density should be kept when laying eggs, generally about 800,000 eggs per cubic meter of water; hatching water should be clean and free of pollution, and there should be a large flow; Water, can be used to control lime slurry in the reservoir, so that the pH value is maintained between 7-8; if a small amount of fish eggs in the hatching pond are found to be stripped in advance, the small inlet valve can be closed and permanganate can be closed properly. Potassium solution was poured into the hatching pond, so that the pool water was 5-10ppm concentration, and kept for 5-8 minutes. After treatment, the egg membranes of the fish eggs became more solid, not easily damaged, and had the effect of preventing premature release.

Second, over-ripe fish eggs, as well as malnourished broodstock fish eggs, most likely to form deformed embryos. Changes in temperature, especially at the fertilization stage of the eggs, at the beginning of cleavage, and before and after the release of the membrane, can lead to an increase in abnormal embryos. Poor hatchery water quality also affects the normal development of the embryo and produces deformed embryos. Therefore, once a year's fry breeding work, it is necessary to do a good job of broodstock cultivation, but also to select the right time for the appropriate broodstock production.

Third, the sword leeches are the biggest enemy of the fry hatchery stage. When it invades a large number of hatching ponds, it will bite fish eggs or bite dead fish. Therefore, spawning ponds and hatching pond waters must be strictly filtered. If it is found that there is more water in the hatchery pool, the water inlet valve may be closed appropriately, and the amount of water in the fish eggs can be prevented from sinking, and then the medicine is used to kill the sword blisters in the pool.

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