NECROTIC MYOSITIS IN CAGE CULTURED RAINBOW-TROUT, ONCORHYNCHUS-MYKISS(WALBAUM), CAUSED BY FLEXIBACTER-PSYCHROPHILUS

A severe necrotic myositis characterized by large intramuscular bullae was identified in 100-500 g rainbow trout, Oncorhynchus mykiss (Walba um), maintained in freshwater netpens. Mortality increased as the temp erature decreased, with mortality rates peaking at 10% per month. Flex ibacter psychrophilus was recovered from the muscle lesions and kidney s of affected fish. The gross and histological description of the dise ase, and the phenotypic characteristics of the causative agent are des cribed. The necrotic myositis isolate was utilized to experimentally r eproduce the disease.