Experimental infections of shing Heteropneustes fossils were conducted with Aeromonas hydrophila to test the pathogenicity of the bacteria in this fish and to determine the median lethal dose (LD50) of the bacteria. Previously isolated and characterized A. hydrophila (CK602) was injected intraperitoneally to shing of 35 g body weight at two doses of 105 and 108 CFU/fish. All experimentally infected fish died within 15 days. In the next experiment, to calculate the LD50 of the pathogen, four different doses viz. 105, 105, 107 and 108 CFU/fish were injected to each group of 10 shing of average body weight 35 g. Mortality was found with the doses between 108 and 108 CFU/fish. LD50 was calculated to be 9.6 x 108 CFU/fish.