Analysis on the prevention and treatment of fish disease of rainbow trout raised in brackish water

Rainbow trout is a kind of cold water and widely salty fish. it is famous for its delicious meat and rich nutrition. it has high economic value and is one of the excellent farmed species in the world. Jingtai County is one of the driest areas in central Gansu Province, lack of fresh water resources, but with a certain flow of brackish water resources, suitable water temperature, water quality in line with pollution-free aquaculture standards, suitable for rainbow trout culture. In order to broaden the channels to increase farmers' income, we have carried out the trial culture of brackish water rainbow trout. After several years of development and utilization, under the condition of salinity 4.7 and flow rate 0.05 ~ 0.06 cubic meters per second, the seedlings were cultivated successfully, the yield per mu of adult fish exceeded 10,000 kg, and the culture effect was obvious, and the meat taste of rainbow trout was more delicious than that of freshwater rainbow trout. the market demand is more exuberant, and the breeding prospect is promising. However, in the process of increasing development efforts and expanding the scale of culture, due to the lack of experience in disease prevention and control, it has caused certain losses to fishery production and affected the rapid development of brackish water rainbow trout culture industry. To explore the causes of rainbow trout under brackish water conditions and to find effective control methods has become a necessary topic for our research. After years of efforts, the author has made some progress in disease prevention and treatment. The main points of disease prevention and treatment are introduced as follows.

First, pay attention to scientific feeding, adhere to prevention, prevention is more important than cure

Strictly follow the technical operation rules of rainbow trout production and raise them scientifically. The construction structure of ① fish pond is reasonable to ensure the smooth flow of water. The culture pond should be fully exposed before stocking and thoroughly sterilized with 100,150kg quicklime per mu. ② put in the seedlings with good varieties and strong physique, and the seedlings should be neat in specification, quick in swimming, strong in physique, disease-free and injury-free, and the breeding density should be suitable. ③ feed nutrition should be comprehensive, pay attention to hygiene, not deteriorate, not single, reasonable processing technology, regular and quantitative feeding, but hungry and full. ④ should do a good job in epidemic prevention and it is strictly forbidden to bring pathogens. Before entering the pool, soak in 2%-3% saline or 10 mg / L potassium permanganate for 10 minutes and then enter the pool. ⑤ pays attention to cleanliness and hygiene, the bottom of the pool does not accumulate dirt, the water is not muddy and does not pollute. ⑥ pull the net carefully so as not to injure the fish. ⑦ should pay attention to the drying and disinfection of tools and the regular disinfection of fish ponds. The fish pond must be cleaned before disinfection, pay attention to observation during disinfection, and strictly prevent dead fish from hypoxia.

Second, continue to patrol the pond and pay attention to the activities of fish schools at all times.

Every morning when patrolling the pond and each feeding, pay attention to whether the activity of the fish is normal, especially pay attention to the change of body color and the number of dead fish. Abnormal activity is the key to the discovery of fish diseases: first, a slight increase in the number of dead fish, it should be thought of as a sign of disease; second, the appearance of fish blackening or yellowing is a sign of disease; third, if the number of fish swimming away from the group increases and is slow to respond to the outside world, it indicates that the school of fish is abnormal; fourth, if the fish have lost their appetite, it may be a sign of poor feed quality and smell, or a sign of insufficient dissolved oxygen, water pollution or disease. Fifth, the fish is very unstable in the water, jumping up and down at one time, swimming wildly at the same time, one may be invaded by parasites, or there may be toxic substances in the water, and the fish may be poisoned. When it is found that the fish have symptoms of disease, the body surface, Gill and intestinal tract of dead fish can be examined routinely, so as to provide a basis for further judging the cause of the disease. Insist on sampling and testing every half month.

III. Adhere to scientific and safe use of drugs

Safe use of drugs plays a key role in the prevention and treatment of fish diseases. First, the use of environment-friendly and improved fishery drugs; second, the use of fishery drugs without "three certificates" (production license, approval number and production batch number); third, the use of three-effect (efficient, long-acting, quick-acting) and three small (small toxicity, small side effects, small dosage); fourth, symptomatic use of drugs, correct use of drugs, not blind use of drugs, abuse of drugs, the dose should not be too large or too small, strictly follow the instructions for use Fifth, the medicine in the feed should be mixed well and processed into particles to feed the fish. Antibiotics and hormones are not added to the feed for a long time to prevent fish from producing drug resistance.

IV. Prevention and treatment of common diseases

In the process of raising brackish water rainbow trout, Vibrio disease, furunculosis, water mildew, enteritis, liver steatosis and other diseases do great harm to fishery production. ① vibrio disease. The diseased fish eyes are protruding, turbid or bloodshot, bleeding from fin base, oral cavity and anus, intestinal congestion, inflammation and inelasticity, blood spots in the liver, splenomegaly and kidney swelling. Prevention and treatment: with sulfonamides mixed with bait, 100 mg per kg of fish body weight was added, and the dose was halved after 2 ~ 4 days. ② furunculosis. Irregular round blood vesicles appeared in the muscle tissue of diseased fish, and others were the same as vibrio disease. Prevention and treatment: 100 mg of sulfonamides or 80 mg of erythromycin per kg of fish body weight were processed into bait and fed continuously for 3 days. ③ water mildew. White filaments appear in the focus of diseased fish, it is difficult to swim in severe cases, do not eat, and travel alone. Prevention and treatment: wash the diseased fish with 3%-5% salt water for 5 minutes. ④ enteritis. Sick fish anus red and swollen, intestinal redness and congestion, no food, severe intestinal pus, sometimes blood, sometimes yellow water, the whole intestine is purplish red. Prevention and treatment: clean the sewage pool, keep the water quality clean; feed fresh feed, eat now; add 3%-5% garlic to the feed and feed for 3-6 days. ⑤ liver steatosis venereal. The color of the negative body is black, the head is darker, the Gill color becomes lighter, severe anemia, swimming slows, sometimes the dorsal fin is out of the water, do spiral movement, and sometimes stand still at the slow flow. Laparotomy showed that the liver was yellow, yellowish-white or light brown, sometimes hyperemia, sclerosis, swelling or shrinkage. The gallbladder is enlarged, yellow and translucent. The ulcer at the end of the intestine is congested and contains yellow mucus. Prevention and treatment: do not feed deteriorated feed: change the feed formula, feed fresh feed and fresh animal feed, feed less or no feed with high fat and carbohydrate content; add VE, VB1 and other vitamins to the feed; increase water flow, discharge sewage and improve water quality conditions.