Fish Diseases and Management

5.1.2 Pasteurellosis

It is the bacterial disease caused by Pasteurella piscicida first reported from white perch in U.S.A. in 1963. The affected fish show prominent white granules in the kidneys and spleen. Pasteurellosis is one of the most important bacterial disease among young cultured marine fish in Japan.

Clinical signs and pathology varies with the form of disease. In acute cases, the body will be darkened , and internally granulomatous – like deposits may develop in the kidney and spleen. Hence, the name pesudotuberculosis. In histopathological studies, the tubercle like lesions composed of masses of bacteria, epithelial cells and fibroblasts.

Pasteurella piscicida is a Gram negative short rod (0.6 – 1.2 x 0.8 – 2.6 m m) which exhibits characteristic bipolar staining. It is non-motile, non-capsulated and non-spore forming. Serological tests such as slide agglutination using specific antigen or direct and indirect fluorescent antibody techniques can be used for definitive diagnosis.

When the water temperature increases to 25⁰C or more or when the salinity is reduced by long term rain, pseudotuberculosis caused by P. piscicida appears in fish farms in Japan. P. piscicida does not survive for more than 4-5 days in marine waters.

Avoidance of over crowding and feed management may prevent out-breaks of this disease. Ampicillin, amoxicillin, novobiocin, chloramphenicol florfenicol, oxolionic acid, flumequin and sodium nifurstyrenate are used to control bacterial pseudotuberculosis.