Channa punctatus was exposed to Aeromonas hydrophila for 21 days at a concentration of 103 and 105 CFU dilutions. Exposure to 7th, 14th and 21st days, the fish showed severe histological changes in the gills, intestine and liver tissues. Initially degenerative changes like hypertrophy of epithelial cells and dilution of the marginal channel and abnormal intestinal villi occurred in the intestine, later disorganization of the serosal layer and hyperplasia, haemorrhagic septicemia of the intestinal villi, liver cord disarray, vacuolation of the cytoplasm and necrosis was observed. Rupture of lamellar epithelium leading to haemorrhage of gills, goblet cell damage and mucous secretion of intestinal villi and degeneration of the liver parenchyma were recorded in an increasing order towards days after exposure. Thus, the histological alterations were, observed according to the hours of exposure to Aeromonas sp.