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 is rough, easy to make the eggs floating with the water floating Broken; Third, the ovulation density is too large, or the quality of the hatchery water is poor, the pH value is low or high; Fourth, several hatching pools use recycled water at the same time, and the hatching time of each hatching pool is not the same. The eggs hatched in the hatching pool are released as early as possible, and the egg membrane-dissolving enzymes released into the water enter the hatching pool of the fish eggs 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 to keep the pH between 7-8. If a small amount of fish eggs in the hatching pond are found to be removed in advance, the inlet valve can be closed and permanganate can be closed. Potassium solution is poured into the hatching pond, so that the pool water shows a concentration of 5-10ppm for 5-8 minutes. After treatment, the egg membranes of the fish eggs will become more solid, not easy to damage, and have 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 kill larvae. Therefore, spawning ponds and hatchery ponds must be strictly filtered. If it is found that there is more water in the hatchery, the water inlet valve can be closed appropriately. The amount of water in the fish eggs can be undulated without sinking. Then 80% of the dichlorvos emulsion is used to splash water into the hatching tank and immediately stir manually. Rice pond water 200 milliliters of medicine, in the water temperature of 30 °C -28 °C, 10-30 minutes can kill the pool of water swords. Or drill a few holes in a plastic bottle filled with 90% crystal trichlorfon, and hang it in the reservoir to the water supply port of the hatchery to poison the sword water cricket.