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, which has lost the protection of the egg membrane, sinks and then dies.
First, the cause
First, the quality of fish eggs is poor, or the fish eggs are overcooked, the egg membrane is brittle and elastic, and it is easily damaged; second, the inner wall of the hatching pool is rough, and it is easy to make the egg membrane floating and floating with the water flow to be scratched; The ovulation density is too high, or the quality of the hatchery water is poor, and the PH value is low or high. Fourth, several hatching ponds use recycled water at the same time, and the hatching ponds have different time to enter the egg. The fish eggs are released as early as possible, and the egg membrane-dissolving enzymes released into the water enter the hatching pool of the fish eggs as circulating water enters, causing the fish eggs hatched in the pool to be released earlier.
Second, prevention and control measures
1. The rough wall of the hatching tank must be smoothed with a grinding wheel; when the eggs are laid, the appropriate density should be mastered, generally about 800,000 eggs per cubic meter of water; the hatching water should be clean without pollution, and have a large flow; Water, can be used to control the lime slurry in the reservoir, so that the PH value is maintained between 7 and 8; if a small amount of fish eggs in the hatching pond are found to be released in advance, the small inlet valve can be closed and permanganate can be closed. Potassium solution was poured into the hatching tank, so that the pool water showed a concentration of 5 to 10 PPM, and maintained for 5 to 8 minutes. After treatment, the egg membranes of the fish eggs became firmer, not easily damaged, and had the effect of preventing premature release.
2. Over-ripened fish eggs, as well as fish eggs produced by malnourished broodstock, are most likely to form deformed embryos. Changes in temperature, especially at the fertilization stage of the eggs, at the beginning of the cleavage, and before and after the release of the membrane, can lead to an increase in deformed 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 breeding, but also to select the right time for the appropriate broodstock production.
3. Jianshui is the biggest enemy of the fry hatching stage. When it invades a large number of hatching ponds, it will bite fish eggs or bite dead 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, and then 80% of the dichlorvos emulsion is used to splash water into the hatching tank and immediately stir manually, every cubic meter. Rice pond water 200 milliliters of medicine, when the water temperature 28 °C ~ 30 °C, 10 to 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 water supply port from the reservoir to the hatchery to poison the sword.