Control methods for common fish diseases in early summer
In early summer, water temperatures are suitable, and various pathogens readily breed and multiply, making it a season when fish become ill. If prevention is neglected, fish diseases are easily triggered. Grass carp in particular have a high mortality rate when they fall ill, causing great losses. The symptoms and control methods of four major fish diseases are introduced below:
1. Saprolegniasis:
Symptoms: local injury to the fish body, loss of scales, mold or fuzz on the body surface. Abnormal swimming, reduced feeding, leading to emaciation and death. Cause: mainly injury to the fish body after harvesting, after which the disease invades the weakened fish and causes illness.
Control methods: (1) During harvesting, transport and stocking, take care to protect the fish body from injury. (2) When stocking fry, soak the fish in 5% salt water for 5 to 10 minutes. The length of soaking time depends on the air temperature at the time and the fish's tolerance. (3) For each mu, for each meter of water depth, use 30 kg of quicklime mixed with water and splash it over the whole pond.
2. Enteritis:
Symptoms: enlarged abdomen, red spots, protrusion, redness and swelling, congestion of the abdominal microvessels, formation of blood clots, and overflow of mucus. Epidemic situation: generally from April to September. The mortality rate of 1- to 2-year-old black carp and grass carp reaches 5% to 90%.
Control methods: (1) Use 1 mg per liter of bleaching powder or 25 to 30 kg of quicklime mixed with water and splash it over the whole pond. (2) For every 10,000 fry or 50 kg of adult fish, use 250 g of garlic bulbs, 200 g of salt and 5 kg of bait, mix into balls and feed, for 3 to 6 consecutive days.
3. Gill rot (also called black head disease):
Symptoms: gills rot and become congested, there are open skylights at the edges of the gills, the mucus in the gills sticks the gill filaments together, affecting respiration, and finally leading to death by suffocation. Epidemic season: April to October. When the water temperature is 28°C to 30°C and the pond water pH is between 6.7 and 7.5, the disease is most severe from the Beginning of Autumn to the Autumn Equinox.
Control methods: (1) Use 1 mg per liter of bleaching powder mixed with water and splash it over the whole pond. (2) For every 5 kg of bait, add 10 g of methamidophos, mix and feed. (3) For each mu, 200 to 300 g of methamidophos may also be mixed with water and splashed over the whole pond. Any one of the above three methods may be chosen.
4. Grass carp hemorrhagic disease:
Symptoms: red spots appear on the mouth, lower jaw, top of the head, eyes and body surface. The gills are bright red, and parts of the intestinal tract are also bright red. The intestines and liver are grayish white. There are blood spots on the swim bladder, the gallbladder is congested, and lesions are present in all parts.
Control methods: administer rhubarb orally; for every 10,000 fry or 50 kg of adult fish, use 0.5 to 0.75 kg of rhubarb mixed into 10 kg of bait and feed; alternatively, use 1 kg of flour plus an appropriate amount of soybean cake, then dissolve 4 tablets of moroxydine in water and mix with the bait into a slurry, add 50 g of salt, and feed continuously for 3 to 5 days. From the third day onward, reduce the dosage by half.