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Disease Prevention and Control in Mariculture (2)
Huangdao District of Qingdao is located on the shore of the Yellow Sea and on the west bank of Jiaozhou Bay. It is an important sea fish cage breeding base in northern China. Since its inception in the mid-1990s, it has so far exceeded 6,000 net cages, and has produced more than 3 million fishes. There are more than a dozen breeds such as mackerel, black cockroach, large yellow croaker, true sea bream, black seabream, red fish, and gums. However, at the same time as the scale of breeding continues to expand, fish diseases have been correspondingly severed, causing great economic losses to the breeding units and affecting the people’s production enthusiasm. For this reason, in 1999, we undertook the project of the comprehensive prevention and control technology for marine fish diseases organized by relevant departments in Qingdao, and achieved remarkable results through concerted efforts. The results of the study are reported as follows: First, the type of fish disease and control (A) bacterial disease 1. Bacterial enteritis: carp, carp, black carp seedlings, adult fish have occurred. Symptoms: The diseased fish does not ingest food, and the abdomen expands. It was found that there was no food in the intestines, there was abscess in the intestines, and there was water in the abdominal cavity. It mainly occurs in the high-temperature period from August to September, which can cause a large number of fish deaths. Control measures: (1) Add furazolidone to feed, add 1.5 grams per kilogram of feed, feed for 5-7 days; (2) feed fresh fish and shrimp; (3) hang bag of bleaching powder around cage, after 3 days The number of deaths decreased and basically returned to normal after 1 week. 2. Bacterial exophthalmopathy: Occurs in true convulsions. Symptoms: The diseased fish protrudes outward from one or both sides of the eye, and bubbles appear in severe eyes and the eyes fall off. Microscopic examination of the eyes found a lot of Vibrio. Control measures: 110ppm of leukomycin soaked for 30 minutes, used 3 times. 2 Add 3 grams of oxytetracycline per kilogram of feed and feed it for 5-7 days. (b) Diseases caused by parasites 1. Trichodonsis: Occurrence of wintering squid. Symptoms: Increased sputum mucus, lighter, incomplete filament color, dark fish body, slow swimming, or loss of balance. A microscopic worm was found in the microscopic inspection silk. The disease can cause a large number of carp deaths. Control measures: Soak the diseased fish with 1ppm CuSO4 for 30 minutes. When the water temperature drops to 1°C, the concentration increases to 8ppm. Simultaneously add leucomycin 10ppm or chloramphenicol 5ppm. After light soaking, symptoms gradually returned to normal. 2. Cryptomonasae parasitic: Occurs in salmon, black cockroach. Symptoms: The diseased fish swimming slowly, darken body color, increased mucus in the iliac crest, the color of the cocoon filament fades, and there is a small white spot. Microscopic examination revealed Cryptocaryon irritans. Control measures: soak in 100ppm formalin for 10 minutes, or soak in fresh water for 20 minutes, add 5-10ppm chloramphenicol when soaking. After soaking, most of them returned to normal. 3. Double vaginal parasite parasitic: Occurs in carp, carp, black. Symptoms: Diseased fish are out of colon, fish body color is dim, some are out of balance, mucous in the ankle is increased, cocoon filaments are lightened, and brown spots are present. Microscopic examination revealed two vaginal flukes. Control measures: The worm body can be shed by soaking in fresh water or 8% saline or 100 ppm formalin for 10 minutes. 4. Anchor head parasites: Occur in black. Symptoms: The diseased fish is isolated, the snouts of the fish, the fins and diaphragms, parasites 1-2 mm long. When the number of parasites is large, it is hairy. These parasites destroy the epithelium of the cockroach and cause secondary infections and death of the fish. Control measures: Soaking with 1ppm trichlorfon for 10 minutes, or soaking with 100ppm formalin for 10 minutes, can make the body fall off. After 3 days of soaking, the lighter fish returned to normal. 5. Starch egg dinoflagellates: Occur in puffer fish, real salmon. Symptoms: Diseased fish do not ingest, dark in color, swim in excursions, bleeding in the snout, increased mucus in the ankle, pale in color, and white spots. Microscopic examination revealed that a large amount of black starch dinoflagellate trophozoites were produced on the surface of the ankles, fins and skin. The disease can cause massive fish deaths. Control measures: Soak for 30 minutes with copper sulfate and ferrous sulfate 0.7ppm per day for 3 days, or soak in fresh water for 30 minutes, wash once every other day. (C) Nutritional Diseases Hyperlipidemia: Occurs in salmon, sea bream and puffer fish. Symptoms: The diseased fish swim slowly and looks dull. Anatomical findings revealed a massive yellowing of the liver, yellow-green bile ducts, and massive yellowing of the abdominal fat. Control measures: Feed fresh feed and add vitamin C and vitamin B. Can alleviate the condition, but it is difficult to recover. (D) viral diseases 1. Lymphatic leukemia: really suffer from the disease. Symptoms: The diseased fish loses its appetite, swims on the surface of the water, and sinks after death. Extremely anemic, with albino body color, gray to grayish white, pale red to white, green liver, or dark red to pink, brown markings. More popular in the low water temperature period. Prevention and control measures: Initially found to be caused by a virus, secondary infection by solitary bacteria and ulceration. Can be used antibiotic prophylaxis, feeding complex vitamins. 2. Lymphocystis disease: The disease is found in carp and carp. Symptoms: Single or swarming small pearl-like or blisters-like swellings on the head, trunk skin, fins, and tail of diseased fish. The lymphatic cysts of diseased fish do not form a group and they are scattered. There are well-developed melanocytes around the diseased fish, with small black spots on the outside. The infection rate can reach 30%. The disease is susceptible to secondary bacterial infections. It is endemic during periods of high water temperature and is not fatal. Viruses may shed or infect other fish from the site of cyst rupture. Preventive measures: Can be used to deal with bacterial diseases, there is currently no other good treatment. II. Discussion and Suggestions At present, the scale of fish farming in cages has been expanding year by year, which has become a new growth point in the marine fishery economy. However, due to the fact that they are mostly restricted to inner bay farming, the density of local breeding is too large, and there are too many aquaculture species, which results in poor water flow and poor seawater exchange. Various waste water and waste oil on the land bank are discharged into the sea to cause pollution, coupled with the prevention of fish diseases by farmers. Insufficiency, and living rubbish on the raft, dead fish was not timely sent to the shore to bury, excessive feeding of small trash fish, residual bait deposition, so that the proliferation of various pathogens in the sea area, a high temperature season, leading to fish disease spread. In order to promote the healthy development of marine cage fish farming, it is recommended to develop new marine fish cage breeding sea areas and actively develop deep-water storm-resistant net cage culture: strengthen macro-management, control the density of fish farming, and rationally distribute, promote water circulation in the sea area, and change the amount of feeding. Strengthen the management of residual baits and dead fish and diseased fish to reduce the occurrence of fish diseases; strengthen waste water and waste management and control and management of land-based pollutants, and improve the water quality and environment of the sea area.