One, the cause of dead fish
1, severe weather. The main reason is the abrupt change of weather and sudden drop in temperature, which makes it difficult for fish to adapt to and tolerate pathological changes, resulting in massive deaths.
2. Hypoxia caused death. In winter, due to the freezing of water in the pool, coupled with the continuous cloudy and snowy weather, phytoplankton cannot add photosynthetic dissolved oxygen, and atmospheric pressure and wind waves can not increase oxygen directly, resulting in oxygen deficiency in pool water, especially in intensive pools due to dense fish Oxygen consumption is high, and it is more likely to cause the death of fish with hypoxia.
3, sludge hazards. The intensive culture of high-yield pools, due to the constant accumulation of fish manure, residual baits, organic fertilizers, etc., and the mixing of silt, form a certain thickness of silt in the bottom of the pool. The sludge contains a large amount of organic matter, and the organic matter is oxidized and decomposed by the action of bacteria. The consumption of large amounts of oxygen often results in the exhaustion of oxygen in the lower water of the pond, resulting in a severe lack of oxygen. Absolute dominance of bacteria in sludge, fermentation of organic matter, production of a large number of reducing intermediates—ammonia, nitrite, and subsequent reduction and decomposition to produce hydrogen sulfide (blackening sludge is an important indicator of the presence of hydrogen sulfide ). Ammonia, nitrites, and hydrogen sulfide are highly toxic substances that fish live and grow, and can cause large numbers of fish deaths.
4, disease. Generally, due to the low temperature and water temperature in winter, it generally does not cause major outbreaks and epidemics. However, due to netting and ponding before the winter, fish injuries, weak constitutions, or lack of preventive measures can also cause fish. A lot of death.
Second, preventive measures
1, clear pond in addition to silt.
Before stocking in intensive culture ponds or during the winter when fish are stored in winter, clear ponds are first used for silt removal, and then 100-150 kg of lime are used for clear ponds per acre. It not only kills intermediate hosts of viruses and pathogens, but also neutralizes organic acids, hydrogen sulfide, etc. in the sludge, alters the acidic environment, makes the sludge alkaline reaction, and is conducive to the survival of fish in winter. In addition, the quicklime clear pond can also clarify the turbid pool water, make the suspended colloid organic matter cement and precipitate, and enhance the ability of the phytoplankton to produce oxygen in photosynthesis.
2, change the traditional fertilization method.
In the case of intensive fertilization, cockroach, or cultivation of large-scale ponds and oysters, it is often the case that large amounts of organic fertilizers are directly put into the pool and sink to the bottom of the pond. Some have not been used until the clear ponds in the autumn, causing great harm. . If a 2m0.4m2m fertilizing cage with a mesh size of 3mm is used, the fermented organic fertilizer is placed in a box and flushed with water to dissolve the manure in water. The remaining organic fibers and debris are removed from the tank. Out, can greatly improve fertilizer utilization, reduce pollution of water quality.
3, to do the preparatory work before winter.
Before wintering, intensive intensive ponds should strengthen feeding and management to enhance the fish's constitution, and the pond should not be too dense during the winter, as far as possible to avoid fish injuries. Fish disinfection before winter to kill pathogens.
4. Clean the snow on the pond ice or add new water.
After the pond is frozen on the water surface, the snow should be cleared in time in case of snow to prevent the snow cover from affecting the photosynthesis of the phytoplankton in the water, which is not conducive to the increase of oxygen in the pool water. In addition, it is also possible to adopt a method of constantly infusing new water so that the snow covering the surface melts.
5, keep part of the pool water does not freeze
After the pool water is frozen, harmful gases cannot escape naturally and it is very easy to cause fish poisoning and death. A better method is to install a 2.2kW submersible pump on one side of the intensive culture wintering pond. When the pool water is frozen, the water is turned on for 0.5 to 1 hour every day to keep the water in the pool from freezing for one third.
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