Pathogenicity of a bacterial isolate Aeromonas hydrophila recovered from naturally diseased shing fish was investigated against catfishes (Heteropneustes fossilis and Clarias batrachus), carps (Labeo rohita, Catla catla and Cirrhinus cirrhosus) and perch (Anabas testudineus) of average body weight of 20.4 g for H. fossilis, 25.6 g for C. Batrachus, 35.2 g for L. rohita, 25.7 g for C. catla, 30.5 g for C. cirrhosus and 20.3 g for A. testudineus. Two different doses viz. 6.7 × 10 6 and 6.7 × 10 5 CFU/fish were injected intramuscularly. Pathogenicity of A. hydrophila was confirmed at water temperature of 30°C by mortality of 60% to 100% of all the tested fishes within 2-11 days. Injected A. hydrophila was re-isolated from liver, kidney and intestine of all the tested fishes. The highest bacterial loads in catfishes were found to be 5.5 ×