How can cold-water fish farming effectively prevent and control pathogens?

1. Establish a strict quarantine system. When introducing and exporting fish eggs and fry, all farming areas must strictly carry out quarantine to prevent and control the occurrence of diseases. Farms should set up quarantine ponds to isolate introduced fish species; only after the introduced fish are confirmed free of important diseases may they be temporarily reared. Quarantine ponds are generally located at the end of the drainage ditch. The length of quarantine time should be determined by the transport season, water temperature, and the characteristics of the disease. When the average temperature is not lower than 12°C, 20 days are required; when the water temperature is higher, it can be shortened, which is determined on the basis that the lower the temperature, the longer the incubation period. If new species are transplanted to a new area, because of the sudden change in climatic conditions, 1 year of quarantine time is required. This is because some parasites and microorganisms that are almost harmless to local fish species may cause serious harm to the introduced species.

2. Pond disinfection. First drain the pond water, then disinfect once a month with 130-330 kg/mu of quicklime, or 160 kg/mu of calcium cyanamide, or 5% calcium hypochlorite. The farming area and its surroundings should maintain environmental hygiene and site cleanliness. Non-working personnel, vehicles, livestock, etc. must not enter the farming area. Spray and disinfect the environmental area once a month with trichloroisocyanuric acid.

3. Fish body disinfection. Fish body disinfection uses the medicated bath method. The commonly used disinfectant drugs are as follows. (1) Salt: prepare a concentration of 2%-4%, soak and wash for 5-10 minutes, mainly to prevent bacterial gill rot disease, protozoan disease, gyrodactylosis, etc. (2) Bleaching powder (containing 30% effective chlorine): use a concentration of 10-20 mg/L, soak and wash for 10-30 minutes, can kill bacteria on the body surface and gills. (3) Potassium permanganate: use 10-20 mg/L, soak and wash for 10-30 minutes, can kill bacteria, protozoa, and gyrodactylids on the body surface and gills. Potassium permanganate is an oxidizing agent and should be prepared just before use, and the water used for the medicated bath should be clear water containing relatively little organic matter, and the medicated bath should be carried out away from light. (4) Povidone-iodine: use 0.5%-1.5% polyvinylpyrrolidone iodine to disinfect fish eggs at a concentration of 50 mg/L, soak for 15 minutes, can prevent viral diseases such as infectious pancreatic necrosis, infectious hematopoietic necrosis, viral hemorrhagic septicemia, etc.

4. Tool disinfection. Various tools used in farming often become vectors for spreading diseases, so workers and their rain boots, leather pants, gloves, etc. must be disinfected when entering and leaving the farming area. Materials and fishing gear are dedicated to the farming area, should be properly kept, and disinfected before use. Vehicles entering the farming area must be disinfected to strictly prevent cross-infection. Tools used in diseased ponds should be separated from tools used in other ponds to avoid bringing pathogens from one pond into another. If tools are insufficient and cannot be used separately, tools used in diseased ponds should be disinfected before use. Generally, nets can be soaked and washed in a copper sulfate aqueous solution at a concentration of 20 mg/L for 30 minutes, dried in the sun, and then used; wooden tools can be disinfected with a 5% bleaching powder solution, rinsed clean in clear water, and then used.

5. Feeding ground disinfection. Every day, remove leftover bait and clean the feeding ground. During the disease epidemic season, regularly sprinkle bleaching powder and trichlorfon around the feeding ground to sterilize and kill insects. The amount should be determined according to the size of the feeding ground, water depth, water quality, and water temperature, generally 250-500 grams:

6. Drug prevention. For drug prevention of external diseases, Chinese herbal medicines can be tied into small bundles and placed at the water inlet to steep in the water, or bactericides and insecticides can be sprinkled over the whole pond to achieve the purpose of killing external pathogens; drug prevention of internal diseases generally adopts the oral method, mixing preventive drugs in a certain dosage into the bait to make granular medicated bait for feeding. The types of drugs used vary with various diseases. Use Chinese herbal medicines and vaccines as much as possible to avoid drug resistance.