About the BookIsolation and enumeration of heterotrophic bacteria, lactic acid producing bacteria such as Lactobacillus species and fish pathogens such as Salmonella species, Vibrio species, Pseudomonas species and Aeromonas species from the gastrointestinal tract of mrigal, Cirrhinus cirrhosus has been carried out to find out their importance in the nutrition of the host fish. Amylolytic, proteolytic and cellulolytic bacteria were detected in the mrigal fish gut. Among specific enzyme producing bacteria, amylolytic and proteolytic bacteria were present at higher number with in the gut of mrigal fish, respectively selected intestinal isolates were analyzed for extracellular enzyme producing capacities. Amylase and protease activities were exhibited by bacterial the strains isolated from the mrigal fish gut. The information generated from the present investigation might contribute to the utilization of these extracellular enzyme-producing bacteria in commercial aquaculture.