Occurrence of bacteria species responsible for vibriosis in shrimp pond culture systems in Sri Lanka and assessment of the suitable control measures

Shrimp culture in Sri Lanka is continuously affected by bacterial infections and most symptoms agree with the disease called vibriosis. Therefore a bacteriological study was undertaken in shrimp farms to identify the diversity of pathogenic Vibrio species, favorable environmental conditions for them and sensitivity to antibiotics to control them. Water and infected animals from shrimp farms of the Western and North Western provinces were screened for Vibrio . Conventional methods were used for presumptive identification of isolated bacteria. Water quality was analyzed by spectophotometric methods. Disk diffusion technique was used to evaluate antibiotic sensitivity. During the study, 40 bacteria isolates belonging to the family Vibrionaceae were recorded. Of those, 24 isolates belonged to Vibrio species which are responsible for vibriosis in shrimps. Those were Vibrio alginolyticus , V. parahaemolyticus , V. damsela , and V. anguillarum . Most frequently isolated species was V. parahaemolyticus . All Vibrio isolates were found to be resistant to Ampicillin, Gentamycin, Oxytetracyclin, Chloramphenicol, Trimethoprim and Kanamicin, which are commonly used antibiotics in aquaculture. Water quality conditions indicated that the alkaline pH conditions and high salinity and ammonia levels favour the occurrence of high vibrio counts. Results indicate that the application of antibiotics for the control of vibriosis in shrimp farms has limited effectiveness due to the development of resistant bacterial strains and environmental management is the best management intervention that can be used to control this disease.