Fourteen strains of Bdellovibrio-like organisms were isolated from cultured fish ponds using Aeromonas hydrophila J-1 as host, one of them formed large plaques after 48 h of incubation at 28°C on a double layer plate, designated as Bdellovibrio C-1. The Bdellovibrio was confirmed by electron microscopy and PCR amplification of Bdellovibrio-specific 16S rDNA. The optimum temperature for the growth of BdC-1 was between 15–37°C and with optimal activity at temperatures of 25–30°C. The ability of BdC-1 to lyse A. hydrophila was similar in the pH range of 6.5 to 8.5. It can lyse 23 Gram-negative bacterial strains comprising three genera of fish pathogens and one strain of Escherichia coli but cannot lyse Gram-positive bacteria such as Bacillus subtillis and Staphylococcus aureus. Immersion of fish in water containing different concentrations of BdC-1 was used in protection against an experimental infection of A. hydrophila J-1. Results show that the mortality of groups immersed with BdC-1 was lower than the group without BdC-1. These results suggest that it may be possible to use Bdellovibrio to control the disease caused by A. hydrophila.