What are the prevention and control methods for fish diseases and enemies?

1. Blue-green algae disease: Blue-green algae include Microcystis aeruginosa and Microcystis flos-aquae. They generally occur in summer and early autumn, and they like to grow in water with higher temperatures and relatively strong alkalinity. When the pH is 8-9.5 and the water temperature is 28°C-32°C, they reproduce fastest. If there are more than 500,000 colonies per liter of water, the dissolved oxygen in the water is often insufficient for their needs, and they will die in large numbers on their own. After the algal bodies die, proteins decompose easily, producing toxic substances such as hydroxylamine and hydrogen sulfide. When these toxins accumulate in the water, they can not only poison fish to death, but even cattle and sheep that drink this water can be poisoned to death.

Prevention and control methods: (1) Frequently add fresh water to prevent the organic matter content in the water from becoming too high, and pay attention to adjusting the pH of the water (regularly splash lime) to control the reproduction of Microcystis. (2) Splash 0.7 ppm copper sulfate over the whole pond; after applying the chemical, turn on the aerator or add fresh water the next day. (3) When the algal bodies float up and gather in the early morning, scatter wood ash that has not been dampened, continuing for 2-3 days, and they can disappear; the next day, spread quicklime over the whole pond (15-20 kg per mu) for a better effect.

2. Dinoflagellate disease: The dinoflagellates harmful to fish in ponds include Polykrikos and Gymnodinium. They like to grow in water bodies rich in organic matter, with high hardness, and slightly alkaline, and are more common in warm seasons. Dinoflagellates are very sensitive to environmental changes. If the water temperature or pH suddenly changes, they will die in large numbers. Some species in these two types of dinoflagellates are not easily digested when eaten by fish, and the cause of fish death is poisoning by dinoflagellate toxin produced after large numbers of dinoflagellates die.

Prevention and control methods: (1) Based on the characteristic that these two types of dinoflagellates will quickly die in large numbers when environmental conditions such as water temperature and pH suddenly change, when they reproduce in large numbers, water can be changed immediately so that the pond water temperature and water quality suddenly change and their reproduction is inhibited. (2) Splash 0.77 ppm copper sulfate over the whole pond, which can effectively kill dinoflagellates.

3. Golden algae disease: It mainly refers to the hemolysin and fish toxin secreted when Prymnesium parvum reproduces in large numbers in ponds, causing fish death. The water quality characteristics where Prymnesium parvum thrives are: salinity above 4%-5%, oxide content above 2000 mg/L, water hardness above 40°C, and pH 7.2-9.6. Therefore, fish ponds built on saline-alkali land often experience fish deaths due to poisoning by the toxin of this alga; fish poisoning generally begins in the early morning, but the symptoms are different from gasping at the surface. At first, the fish gather toward the four corners of the pond, but disperse when driven away. As the poisoning worsens, almost all the fish gather and line up along the pond bank, heads toward the shore, motionless, and sometimes even jump onto the bank. When a person walks by and drives them away, they may temporarily scatter, but after the person leaves they immediately gather again. The fish staying by the bank begin to lose balance, lie on their sides, have difficulty breathing, and finally die in a coma.

Prevention and control methods: (1) Splash 0.7 ppm copper sulfate over the whole pond, which can inhibit the function of this alga in secreting toxins or weaken the activity of the fish toxin. (2) Splash 5-10 ppm ammonium sulfate over the whole pond, or apply 1-1.5 kg urea and 2-3 kg calcium phosphate per mu, to reproduce plankton and inhibit the growth of Prymnesium parvum. (3) In the early stage of the disease, the toxic water can be discharged and fresh water added, or the fish can be caught and transferred to a fish pond with non-toxic water quality.

4. Qingni moss disease: Qingni moss includes some species of the three genera Spirogyra, Zygnema, and Mougeotia in the family Zygnemataceae. In spring, as the water temperature rises, it begins to germinate in the shallow parts of fish ponds, growing into wisps of green filaments standing in the water. When it ages, the filamentous bodies break away from the pond bottom, forming clumps of tangled filaments that float to the surface. When young fish swim into the Qingni moss, they are often entangled by the tangled filaments and cannot swim out, causing death. At the same time, a large amount of Qingni moss in the pond also consumes nutrients in the pond water, making the pond water less fertile, so the plankton needed by fry cannot reproduce in large numbers, affecting the growth of fry.

Prevention and control methods: (1) Clear the pond with quicklime, which can kill Qingni moss. (2) In ponds where fish have not yet been stocked, 50 kg of wood ash per mu can be scattered on the Qingni moss so that it cannot receive sunlight and dies. (3) If Qingni moss appears in ponds where fish have already been stocked, 0.7 ppm copper sulfate can be splashed over the whole pond, which can effectively kill Qingni moss.

5. Water net algae disease: Water net algae is a kind of green algae, mostly growing in shallow ditches and ponds, especially in fertile water rich in organic matter, where it reproduces very quickly. When there is a lot of water net algae in a fish pond, it is like many nets spread in the water. After fry mistakenly enter the "nets," they often cannot swim out and die.