Fish Diseases and Management

5.1.6 Vibriosis

The genus vibrio contains Gram negative straight or curved rods which are non spore forming and motile by monotrichous or multitrichous sheathed polar flagella. They are common in aquatic habitats particularly in marine and estuarine habitats. Several species are pathogenic for man as well as marine animals. Metabolism is aerobic or facultative anaerobic and carbohydrates are fermented with the production of acid, but not gas.

V. alginolyticus, V. anguillarum, V .ordali V. Salmonicida, V. vulnificus V. damsela are the major fish pathogenic vibrios. In most of the cases anemia is a feature of vibriosis and was due to haemolysis. The exotoxins produced by these bacteria are proteins and are enzymic in nature. The pathogenic strains have well developed iron sequestering mechanism based on secretion of a siderophore, which induces separation of plasma, and tissue iron from its transferin or ferritin binding protein.

Whenever marine fishes are stressed or traumatised, in wild fish and farmed fish, vibrios are able to produce infection which begins as local hemorrhagic ulcers on the mouth or skin surface, or else local necrotic lesions in the muscle, the orbit or along the edge of the fins.