Pathogenicity of Aeromonas hydrophila bacteria was tested on the stinging catfish
Heteropneustes fossilis. Before artificial infection the morphological, biochemical and
physiological characters of Aeromonas hydrophila were studied. The infections were done
by two different methods, viz., intramuscular (IM) and intraperitoneal (IP) injection. In
infection experiment, each group of 10 fish were injected either intramuscularly or
intra peritoneally with one dose higher than the LD50 dose (9.6 x 107 CFU/fish). All the
fish tested died within 1 to 9 days. Both in cases of intramuscular and intraperitoneal
injection, external pathology were found. Haemorrhagic lesions were evident at the site
of injection. The posterior end of the body surface was found to develop greyish-white
lesion that was extended up to caudal fin. Hyperemic anal region and the fin bases were
also observed. Total bacterial loads in liver, kidney and intestine were determined.
Aeromonas hydrophila could be isolated from liver, kidney and intestine of the
experimentally infected fish. In case of intramuscular injection the highest and the
lowest bacterial load was found to be 2.4 x 107 CFU/g of liver and 2.1 x 102 CFU/g of
kidney and in case of intraperitoneal injection they were found to be 3.6 x 106 CFU/g of
kidney and 1.2 x 104 CFU/g of kidney respectively. It was concluded that A. hydrophila
could cause serious disease condition to Heteropneustes fossilis and its pathogenesis in the
fish was also very efficient.