Isolation and immunohistochemical identification of Flavobacterium psychrophilum from the tissue of catfish, Clarias batrachus

This study deals with the identification of bacteria in paraffin embedded tissue of Indian catfish, Clarias batrachus experimentally infected with F. psychrophilum to ascertain it's precise role in the occurrence and state of carrier stage of coldwater disease in asymptomatic fishes. Significant (P < 0.05) mortality was recorded in C. batrachus of this region due to persistent occurrence of creamish/yellowish with non smooth edged colonies of rod shaped flexible gram negative bacterium, F psychrophillum. Serodiagnosis made through polyclonal antiserum dilutions (raised against H antigen of Aqb Fb-6 isolate in rabbit) revealed that staining intensity of this bacterium was dilution dependent as tissue and smears treated with 1:300 and 1:500 antiserum dilutions conferred close relationship at immunofluorescence level with F psychrophilum and stained deeply in the tissues and smear prepared from liver, kidney and intestine of experimentally infected C. batrachus. Result of this study would be helpful in identifying the fish pathogenic bacteria in carrier fish where mortality occurs without explicit clinical signs of disease.