Detailed Explanation of Key Technical Points for Disease Prevention and Control in Yellow Catfish
The yellow catfish is a bottom-dwelling economic fish widely distributed in China's freshwater bodies. While increasing yield per unit area, raising stocking density and expanding farming area, diseases of the yellow catfish have also gradually increased and become more harmful. Let's take a look together at the common disease prevention and control techniques for yellow catfish!
Mechanical Injury
[Cause] Because the yellow catfish likes to live in groups, its pectoral fins and dorsal fins have hard spines, which easily cause mechanical injuries such as skin abrasions and split fins during production operations and transportation, followed by secondary bacterial and mold infections, with fin rot and growth of water mold as the main symptoms.
[Epidemiology] Mainly injuries after cage-separation operations and long-distance transport of large-sized fingerlings.
[Prevention and Control] Careful handling is required during net training and transportation. When fry are released, the holding time in the temporary rearing cage should not be too long, and the stocking density in the temporary rearing cage should be reduced as much as possible. An appropriate amount of oxytetracycline can be added to the transport water, and before fingerlings are put into ponds or cages, they should be soaked and disinfected with low-concentration potassium permanganate or a 30% salt water solution.
Myxosporidiosis
[Symptoms] The skin tissue of diseased fish breaks down and ulcerates, with irregular small white spots scattered on the body surface, and the fish gradually become emaciated and die.
[Prevention and Control] Prepare a 0.1%-0.5% solution with 90% crystalline trichlorfon and soak the fish for 5-10 minutes, or dissolve 90% crystalline trichlorfon in water and splash it over the whole pond at a dosage of 0.2-0.3 mg/L, repeating once after 1-2 days, for 3 consecutive applications.
Gill Rot Disease
[Symptoms] The head of diseased fish is dark, the gills are pale and covered with mucus, the gill filaments rot, and the inner surface of the operculum becomes inflamed and congested, corroded and sloughed off.
[Prevention and Control] In the early stage of the disease, hang baskets with bleaching powder around the feeding area for prevention and control. When the disease is severe, splash bleaching powder solution over the whole pond so that the drug concentration in the pond water reaches 1 mg/L, or sprinkle Chinese gallnut over the whole pond so that the drug concentration in the pond water reaches 1-4 mg/L. Chinese wingnut leaves can also be used at a dosage of 30 g/cubic m, mashed and scattered over the whole pond.
Hemorrhagic Edema Disease
[Symptoms] Hemorrhagic edema disease is caused by bacterial infection. The body surface of diseased fish turns yellowish, mucus increases, the skin of the pharynx breaks down and becomes congested, forming round holes, the abdomen swells, the anus becomes red and swollen and everts, the head becomes congested, the dorsal fin swells, the bases of the pectoral and pelvic fins become congested, the fin rays ulcerate, and even the abdomen splits longitudinally from the pectoral fins to the pelvic fins, with bile leaking out. A large amount of blood water or yellow gelatinous material accumulates in the abdominal cavity, there is no food in the stomach and intestines, the stomach is pale, the intestines are filled with yellow thick fluid, the liver is earthy yellow, the spleen is necrotic, and there are moldy black spots on the kidney. This disease is most harmful during the nursery or adult fish farming period, and is especially prevalent during fry rearing, with a mortality rate as high as 80%. In high-temperature seasons, this disease is prone to outbreak, comes on fiercely and spreads quickly.
[Prevention and Control] During farming, close attention should be paid to water quality conditions to maintain good environmental conditions, with dissolved oxygen content kept above 5 mg/L, and the stocking density of fry should be appropriately reduced. After the disease occurs, disinfect the water body once a day for 3 consecutive days. When feeding fish meat paste, add 1% table salt to the bait daily.
Water Mold Disease
[Symptoms] Water mold disease is caused by infection with water molds. When water molds first parasitize, no abnormality can be seen with the naked eye. When it becomes visible to the naked eye, the hyphae have already invaded the wound and grow and spread inward and outward, appearing as grayish-white cotton-like attachments. Diseased fish swim abnormally and are restless, until the muscles rot, they lose appetite, become emaciated and die. If fish eggs are covered with hyphae, they become white fluffy ball-like masses, and the moldy eggs become dead fish eggs. It seriously harms eggs during incubation and fingerlings and adult fish with wounds on the body surface. This disease is most likely to occur when water temperature is low, mostly caused by improper handling during netting, box separation and transportation.
[Prevention and Control] During catching, transportation and stocking, try to avoid injuring the fish body, and maintain a reasonable stocking density. Before fingerlings are put into the pond, give them a medicinal bath in a 2-3% salt water solution, and splash methylene blue over the whole pond so that the pond water reaches a concentration of 2 mg/L, then splash once more after 2 days. Fertilized eggs should be strictly disinfected before incubation, and the water temperature is best controlled at 26-28°C. During incubation, the fertilized eggs should also be disinfected again.