[Biological characteristics and histopathological observation of Vibrio alginolyticus from diseased fish]

Ulcer disease is one of the most serious diseases and a common problem in various stages marine culture including Epinephelus coioides culture of southern China. The isolation and identification of pathogenic bacteria from E. coioides will be useful for monitoring of drug resistance and controlling the outbreak and spread of ulcer disease in E. coioides. The purpose of this study was to characterize the pathogen of E. coioides.

The pathogenic bacteria separated from the liver and kidney of diseased fish were identified through pure culture, artificial infection, automatic tests in bacteriology automatic identification, drug sensitive tests, morphometry, and physiological and biochemical determination.

The strains were characterized and identified as Vibrio alginolyticus. Two strain were selected for virulence tests and all the moribund/dead fish exhibited ulcer disease as that observed in natural outbreak. Drug sensitive tests show that V. alginolyticus was highly resistant to 3 agents including penicillin, whereas sensitive to 5 agents including chloromycetin. Histopathological changes were mainly shown as cell degeneration and necrosis of gill, liver and kidney, and alterative inflammation as a result of inflammatory cell infiltration in the diseased tissue.

The biochemical, physiological tests confirm that V. alginolyticus is the pathogen causing E. coioides vibriosis. The multi-drug resistance among V. alginolyticus suggests strengthened monitoring of outbreaks of V. alginolyticus caused disease in E. coioides culture.