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Not AvailableFish blood contains several antibacterial proteins that play very important role in the immune responses especially innate immune system which has garnered lesser attention when compared to higher vertebrates. The present study reports the antimicrobial property of fish blood on commonly occurring fish pathogens. The reference cultures employed in this study included Pseudomonas aeruginosa, Edwardsiella tarda and Aeromonas hydrophila. Fish blood was aseptically drawn from the caudal vein using 23 gauge sterile needle. The bacteria were inoculated into sterile Brain-heart infusion broth and 1 per cent blood was added to the broth. After inoculation, broth was incubated at 30 degree celsius for 48 h with observations on the bacterial density using spectrophotometer at 4, 8, 16, 24 and 48 h intervals. For comparison, readings of two sets of control i.e. one with BHI broth and blood and another BHI broth with bacteria were taken. The optical density was measured at 4, 8, 16, 24 and 48 h in blood supplemented broth for A. hydrophila ; P. aeruginosa and E. tarda , whereas increase in optical density for A. hydrophila ; P. aeruginosa and E. tarda in control broth was noticed at same time periods. The clear inhibition of growth was noticed for the three pathogens in BHI broth supplemented with fish blood when compared to control broths. The presence of antimicrobial substances in the fish blood is responsible for the inhibition of growth. The antimicrobial substances present in the fish serum was analysed with 10 per cent SDS-PAGE, which revealed proteins of 20, 22, 23, 33, 34, 44, 45, 46 and 65 kDa. In conclusion, growth of fish pathogenic bacteria is inhibited by the presences of antibacterial proteins in fish blood.Not Availabl