Bacterial Strains (Target Organism and probiont): Three strains were used as target organism against which the probiotic bacteria were screened for its antagonistic activity. Three strains V. harveyi, V. parahaemolyticus and V. vulnificus, which were obtained from scrapings of infected fish sample and identified as Vibrio sp by growing in TCBS medium followed by biochemical analysis. The probionts were isolated from seawater, sediment and healthy fish samples.