How to prevent and treat bacterial septicemia in fish?
Prevention and treatment methods for the fish disease bacterial septicemia
1. Pathogens, symptoms and affected species of bacterial septicemia. The disease is mainly caused by a variety of bacteria, primarily Aeromonas hydrophila, Yersinia ruckeri and others. The main symptoms are: in the early stage of the disease, the mouth, head, chest and abdomen, orbit, gill cover epidermis and the base of the fins of the diseased fish become congested; the gill filaments ulcerate and become congested, and in severe cases the gill filaments rot. When the abdominal cavity is opened, there is yellow or red ascites, and the liver, spleen, kidney and gallbladder are enlarged; in some fish the anus is red and swollen with fluid overflow, and the diseased fish shows lesions all over the body, moving sluggishly in the water or swimming wildly in bursts. The main affected species include various crucian carp, blunt snout bream, bream, silver carp and bighead carp, rice field eel, mandarin fish, common carp and others.
2. Main causes of outbreaks of bacterial septicemia. First, deterioration of water quality: too much sludge at the bottom of the pond, excessive feeding and fertilization, deterioration of the water quality and bottom substrate of the fish pond, low water transparency and low dissolved oxygen, which keep the farmed fish living in a harsh environment for a long time, leading to disorders of the fish's immune system and allowing pathogens to invade. Second, nutritional imbalance in fish: under high-density farming conditions, feeding a single type of feed for a long time means that either too much or too little of a certain substance will cause disorders and imbalances in the related functions of the fish, directly affecting the growth, development and occurrence of disease in the fish. Third, long-term inbreeding leads to breed degeneration and reduced disease resistance. Fourth, improper prevention: during farming, disinfection of the fish pond, fingerlings, feeding grounds, tools and water body is not done well, feeding does not follow the scientific "four fixed" feeding method, and in addition, since fish are now farmed in all kinds of water bodies, fish farmers lack disease prevention knowledge and throw dead diseased fish around at will, causing fish to become passively infected and sick.
3. Preventive measures. First, do a good job of clearing the pond and disinfecting it, remove excess sludge from the bottom of the pond, and 10 days before stocking the fingerlings, spread 80-100 kg of quicklime per 667 sq m of water surface (water depth 10 cm) over the whole pond. Second, strictly prohibit long-term inbreeding to ensure stocking of strong fry with high disease resistance. Third, before the fingerlings are put into the pond, soak them for about 20 minutes in a 15-20 g/m3 KmnO4 solution or 3-5% salt water to kill pathogens on the body surface of the fingerlings. Fourth, the stocking density and combination ratio should be determined according to local conditions, the level of feeding and management technology and disease prevention capacity, and the density should not be too high. Fifth, strengthen feeding management, regularly spread quicklime and add fresh water, turn on the aerator at appropriate times when conditions permit, continuously improve water quality, adhere to the scientific feeding method of "four looks" and "four fixed", advocate feeding less but more often, feed natural high-quality mixed feed as much as possible, do not feed spoiled or toxic feed, and ensure the fish eat enough and eat well to improve the disease resistance of the fish. Sixth, do a good job of disinfecting the water body, food and tools. In the main growth season of fish, which is also the main epidemic season of fish diseases, regularly spread chlorine-containing preparations such as strong chlorine essence, ClO2, chlorine king, water body disinfectant spirit, bromochlorohydantoin or bleaching powder over the farming water body, and for acidic water bodies spread quicklime over the whole pond. Tools used in diseased fish ponds must be disinfected, and dead diseased fish found must be promptly removed and buried deep, not thrown around. Seventh, before the disease becomes epidemic, use an insecticidal drug once to kill parasites, and pay attention to the instructions and scope of use of the insecticidal drug to prevent poisoning and death of specially mixed aquatic products such as shrimp, crab, mandarin fish and freshwater mussels in the pond. Eighth, during the epidemic season of the disease, add internal drugs such as Yuxuening, Yukangda or furazolidone to the feed, each time for 5-6 consecutive days, once a month; if fish in nearby ponds have already become diseased, chlorine-containing preparations should be spread.
4. Treatment methods. Since this disease produces lesions all over the body, treatment must consist of a combination of internal administration and external spreading.
Internal drugs include Yukangda, Yuxuening and others, used at 20 g of drug per kg of feed, fed continuously for 5-6 days as one course of treatment. Note that the drug must be fully mixed with the feed, and each feeding amount should be enough for the fish to finish eating in about 1 hour.
The method of using external drugs is: on the first day, use 0.5 g/m3 of crystal trichlorfon or 0.7 g/m3 of CuSO4 and other insecticides to kill parasites on the fish body; on the second and third days, continuously spread 0.5 g/m3 of strong chlorine essence or 0.3 g/m3 of chlorine king, ClO2, water body disinfectant spirit, or 0.15 g/m3 of bromochlorohydantoin, or 1.2-1.5 g/m3 of "90" disinfectant. The main method used in our city to treat this disease in the past three years is: on the first day, spread "Fishery High-efficiency Double-effect Spirit" plus CuSO4 over the whole pond, with the dosage of Fishery Double-effect Spirit being 1 ml/30 m3 of water body, 100 ml per 3000 m3, and CuSO4 at 0.5 g/m3; on the second day, spread a chlorine-containing preparation over the whole pond once more, and the treatment effect is very satisfactory. In addition, in the past 2 years the aquatic improved variety farm of our city has trial-used a mixture of crystal trichlorfon, CuSO4 and FeSO4 dissolved together and spread over the whole pond, with a dosage ratio of 0.6 g/m3 : 0.6 g/m3 : 0.25 g/m3; with this method, a single application is effective, saving labor and money and giving good results, but this medication method is not suitable for ponds where special aquatic products such as crab, shrimp and mandarin fish are mixed-cultured. In addition, after medication, pay attention to observing changes in weather, water quality and fish activity; once fish are found gasping at the surface, try to increase oxygen or promptly add fresh water. On rainy days, stop medication, and during high-temperature periods, spread drugs after 3 p.m. on sunny days to prevent fish from dying from pond-wide oxygen depletion.
After each spreading of drugs over the water body, it is best to spread 30 g/m3 of quicklime dissolved in water over the whole pond one week later, in order to adjust the pH of the water well, improve water quality and reduce recurrence of fish diseases.
2. Main causes of outbreaks of bacterial septicemia. First, deterioration of water quality: too much sludge at the bottom of the pond, excessive feeding and fertilization, deterioration of the water quality and bottom substrate of the fish pond, low water transparency and low dissolved oxygen, which keep the farmed fish living in a harsh environment for a long time, leading to disorders of the fish's immune system and allowing pathogens to invade. Second, nutritional imbalance in fish: under high-density farming conditions, feeding a single type of feed for a long time means that either too much or too little of a certain substance will cause disorders and imbalances in the related functions of the fish, directly affecting the growth, development and occurrence of disease in the fish. Third, long-term inbreeding leads to breed degeneration and reduced disease resistance. Fourth, improper prevention: during farming, disinfection of the fish pond, fingerlings, feeding grounds, tools and water body is not done well, feeding does not follow the scientific "four fixed" feeding method, and in addition, since fish are now farmed in all kinds of water bodies, fish farmers lack disease prevention knowledge and throw dead diseased fish around at will, causing fish to become passively infected and sick.
3. Preventive measures. First, do a good job of clearing the pond and disinfecting it, remove excess sludge from the bottom of the pond, and 10 days before stocking the fingerlings, spread 80-100 kg of quicklime per 667 sq m of water surface (water depth 10 cm) over the whole pond. Second, strictly prohibit long-term inbreeding to ensure stocking of strong fry with high disease resistance. Third, before the fingerlings are put into the pond, soak them for about 20 minutes in a 15-20 g/m3 KmnO4 solution or 3-5% salt water to kill pathogens on the body surface of the fingerlings. Fourth, the stocking density and combination ratio should be determined according to local conditions, the level of feeding and management technology and disease prevention capacity, and the density should not be too high. Fifth, strengthen feeding management, regularly spread quicklime and add fresh water, turn on the aerator at appropriate times when conditions permit, continuously improve water quality, adhere to the scientific feeding method of "four looks" and "four fixed", advocate feeding less but more often, feed natural high-quality mixed feed as much as possible, do not feed spoiled or toxic feed, and ensure the fish eat enough and eat well to improve the disease resistance of the fish. Sixth, do a good job of disinfecting the water body, food and tools. In the main growth season of fish, which is also the main epidemic season of fish diseases, regularly spread chlorine-containing preparations such as strong chlorine essence, ClO2, chlorine king, water body disinfectant spirit, bromochlorohydantoin or bleaching powder over the farming water body, and for acidic water bodies spread quicklime over the whole pond. Tools used in diseased fish ponds must be disinfected, and dead diseased fish found must be promptly removed and buried deep, not thrown around. Seventh, before the disease becomes epidemic, use an insecticidal drug once to kill parasites, and pay attention to the instructions and scope of use of the insecticidal drug to prevent poisoning and death of specially mixed aquatic products such as shrimp, crab, mandarin fish and freshwater mussels in the pond. Eighth, during the epidemic season of the disease, add internal drugs such as Yuxuening, Yukangda or furazolidone to the feed, each time for 5-6 consecutive days, once a month; if fish in nearby ponds have already become diseased, chlorine-containing preparations should be spread.
4. Treatment methods. Since this disease produces lesions all over the body, treatment must consist of a combination of internal administration and external spreading.
Internal drugs include Yukangda, Yuxuening and others, used at 20 g of drug per kg of feed, fed continuously for 5-6 days as one course of treatment. Note that the drug must be fully mixed with the feed, and each feeding amount should be enough for the fish to finish eating in about 1 hour.
The method of using external drugs is: on the first day, use 0.5 g/m3 of crystal trichlorfon or 0.7 g/m3 of CuSO4 and other insecticides to kill parasites on the fish body; on the second and third days, continuously spread 0.5 g/m3 of strong chlorine essence or 0.3 g/m3 of chlorine king, ClO2, water body disinfectant spirit, or 0.15 g/m3 of bromochlorohydantoin, or 1.2-1.5 g/m3 of "90" disinfectant. The main method used in our city to treat this disease in the past three years is: on the first day, spread "Fishery High-efficiency Double-effect Spirit" plus CuSO4 over the whole pond, with the dosage of Fishery Double-effect Spirit being 1 ml/30 m3 of water body, 100 ml per 3000 m3, and CuSO4 at 0.5 g/m3; on the second day, spread a chlorine-containing preparation over the whole pond once more, and the treatment effect is very satisfactory. In addition, in the past 2 years the aquatic improved variety farm of our city has trial-used a mixture of crystal trichlorfon, CuSO4 and FeSO4 dissolved together and spread over the whole pond, with a dosage ratio of 0.6 g/m3 : 0.6 g/m3 : 0.25 g/m3; with this method, a single application is effective, saving labor and money and giving good results, but this medication method is not suitable for ponds where special aquatic products such as crab, shrimp and mandarin fish are mixed-cultured. In addition, after medication, pay attention to observing changes in weather, water quality and fish activity; once fish are found gasping at the surface, try to increase oxygen or promptly add fresh water. On rainy days, stop medication, and during high-temperature periods, spread drugs after 3 p.m. on sunny days to prevent fish from dying from pond-wide oxygen depletion.
After each spreading of drugs over the water body, it is best to spread 30 g/m3 of quicklime dissolved in water over the whole pond one week later, in order to adjust the pH of the water well, improve water quality and reduce recurrence of fish diseases.