First, occurrence and harm
1. Vibrio anguillarum pathogens cause a variety of Vibrio species, including Vibrio anguillarum, V. alginolyticus, and V. parahaemolyticus. This type of bacteria mainly infects the hemolymph. The main reason for this is the high stocking density. During the breeding process, the crabs are mechanically damaged or the enemy invades and damages the surface of the crabs. Water quality is contaminated and excessive feeding of artificial feed results in vibrio. Secondary infection. The abdomen and appendages of the diseased crab rot, their body color becomes lighter, their white color is opaque, and their metamorphosis stagnates. In the diseased crab tissue, especially in the pupa tissues, there are blood cells and bacteria gathered into the opaque white mass, and there are a large number of blood clots in the diseased crab that has died or just died. Diseased crabs are thin and weak, their ability to move is weakened, and they are slow to move. They lie at the edge of the pool. Most swim slowly in the middle and lower layers of the water. Their phototaxis is poor, their body color turns white, their food intake is reduced or they do not eat, and sometimes the crabs become unconscious. . With the development of the disease, the chest and legs have lost their ability to move and eventually gathered to die at the poolside shoal.
The disease is mainly harmful to juvenile crabs, zoea and even large ocular larvae. The incidence rate is higher and the mortality rate can reach more than 50%. If the larvae become infected, it will lead to “destruction of the whole army†within 1 to 2 days. The main epidemic of the disease is summer, and the epidemic water temperature is 25-30°C.
2. The blood lymph smear of the diseased crab is diagnosed. If there is an arc-shaped, spiral-shaped or S-type Gram-negative bacillus, and it has the symptoms of the disease, it can be basically judged as the disease. For the early stage diseased larvae, through the more transparent places, under the 400-fold microscope, the blood lymphatic activity between bacteria in the larvae can be seen. For diagnosis, agglutination tests should be performed using Vibrio polyvalent serum.
Second, control methods
1. Prevention (1) Reasonable stocking, maintaining a suitable density, generally 3 to 6 per square meter, each 5 to 10 grams. (2) During fishing and transportation, care should be taken to avoid crab injuries. (3) Replace new water in time, regulate water quality, and keep water clean to prevent the disease from occurring due to the increase of organic matter. (4) During the nursery period, the nursery pond is sterilized with 15 to 20 mg/L potassium permanganate in the pool, and the nursery tools are soaked in bleaching powder of 50 mg/L for more than 1 hour to prepare fresh water for brackish water use. 10 mg/L bleaching powder disinfection. (5) In the onset season, Quanchiposa 1 mg/L oxytetracycline or 1-2 mg/L bleach for prevention.
2. Treatment (1) Sprinkle with 2 to 3 mg/l oxytetracycline, or 1.5 to 2 mg/l chloramphenicol, or 1 mg/l norfloxacin, once daily, for 3 consecutive days ~ 5 times. (2) Combine oxytetracycline (0.1 to 0.2 g/kg crab) or erythromycin (10 g/kg feed) in the feed to make a pellet feed and feed it for 7 days. Treatment, according to the condition can be fed 1 to 2 courses.
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