A crisis has arisen in the prawn industry in many regions with the onset of disease, with Vibrio spp. being important major causal factors. The value of adding selected strains of Bacillus as probiotic bacteria to control the Vibrio is shown by comparing farms in Indonesia using the same water sources, which contained luminous Vibrio strains. The farms that did not use the Bacillus cultures experienced almost complete failure in all ponds, with luminescent Vibrio disease killing prawns before 80 days of culture were reached. In contrast, a farm using the probiotics was culturing prawns for over 160 days without problems, by using Bacillus at abundances of about 1×10 4 to 1×10 5/ml. The bacterial species composition was different in the pond water on the two farms and demonstrates that it is possible to change bacterial species composition and improve prawn production in large water bodies. Vibrio numbers, especially luminous Vibrio numbers were low in ponds where a large abundance of specially selected Bacillus species was maintained in the water column. Vibrio numbers were also low in sediments and no luminous Vibrio occurred in sediments where the probiotic Bacillus were used.