In the later period of cultivation, as the feeding of feedstuffs increases, the bottom of the fish ponds deteriorates and the pond waters are aged, which is prone to eutrophication, and management must be strengthened. Cause changes in algal populations The eutrophication of water makes it easy to reduce the number of predominant species such as diatoms and dinoflagellates that used to feed the tilapia and is replaced by some non-digestible algae. The color of the water also changes with dominant populations. . The over-proliferation of these algae, on the one hand, forms cloud-like "bloody" on the surface of the water and gives off stench, worsening water quality, affecting the growth and development of tilapia; on the other hand, excessive algae and absorption on the fish gills can affect breathing. After the death of algae, its protein decomposition can produce toxic substances such as hydroxylamine and hydrogen sulfide, threatening the survival of aquatic organisms such as fish. Cause severe fluctuations in dissolved oxygen in the water. During the daytime, due to the photosynthesis of algae and aquatic plants, the dissolved oxygen in the water can be saturated. At night, due to the consumption of oxygen by a large number of algae, algae corpses, organic pollutants, and aerobic bacteria, the water is deprived of oxygen. . In particular, in the summer and autumn, the water temperature is high, and the decomposition of organic matter is fast and the oxygen consumption is greater. At the same time, a large amount of algae covering the water surface will affect the photosynthesis of the middle and lower layers of water, so that dissolved oxygen is vertically layered, which can cause tilapia to suffocate. It is easy to cause fish disease in the whole pond and the accumulation of organic matter in the aquaculture water body can increase, which can lead to the proliferation of pathogenic microorganisms. Once the fish body is damaged, the pathogen quickly invades the wound, resulting in fulminant infection in a short time. For example, the outbreak of freshwater fish has a lot to do with the deterioration of the water environment. Eutrophication prevention
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Eutrophication hazards
Aquatic toxicity enhances eutrophication of water, high levels of nitrates and nitrites, and these compounds are able to form a variety of carcinogenic substances after being sterilized by chlorine preparations. Nitrite, a derivative of nitrite, is itself a strong carcinogen, which is extremely harmful to the growth of tilapia and can easily cause abnormalities in tilapia.
1. Dilution of polluted water by means of water exchange, water injection, etc. to reduce the concentration of nutrients; often open aerators, aerate oxygen, avoid dissolved oxygen layering; scientific feeding and fertilization, no fertilization and organic fertilizer for eutrophic waters To adjust the stocking structure, relatively reduce tilapia stocking and increase the stocking rate of filter-feeding fish; too much algae can also be manually salvaged and removed.
2. Drug management methods: For algal blooms, “bloom†can be sprayed with 0.7 g/m3 of copper sulphate and ferrous sulfate (5:2); regular use of quicklime and bleach can improve water quality and kill harmful algae. And pathogenic bacteria; To the excessive organic matter of the water, oxygenation agents such as calcium peroxide are added to increase the dissolved oxygen, and promote the propagation of other food organisms; if there are more suspended matter in the water, it can also be clarified with alum.
3, the use of biological agents control, spilled biological water purifying agents, such as: chemical energy heterotrophic bacteria, photosynthetic bacteria and a class of highly active microbial agents, which can quickly degrade, transform the organic pollutants and nitrogen, phosphorus and other nutrients in aquaculture water , And can effectively inhibit the growth and reproduction of pathogenic microorganisms and harmful algae in water, reduce the content of toxic substances such as ammonia nitrogen, nitrosonitrogen, and hydrogen sulfide, improve water quality, and promote the rapid growth of cultured organisms.