CEPHALIC OSTEOCHONDRITIS AND NECROTIC SCLERITIS IN INTENSIVELY REAREDSALMONIDS ASSOCIATED WITH FLEXIBACTER-PSYCHROPHILUS

Three cases of pyogranulomatous cephalic osteochrondritis of intensive ly reared rainbow trout, Oncorhynchus mykiss (Walbaum), and Atlantic s almon, Salmo salar L., in Canada and Chile, respectively, were examine d for histopathological and bacteriological changes, and by using immu nohistochemistry. Bilateral exophthalmia and intraocular haemorrhage w ere the most common gross lesions seen in the Ontario fish. Histologic ally, the major pathological changes seen in all cases involved the de veloping bone and cartilage of the head region, including the eye. Nec rosis and pyogranulomatous inflammation of the scleral cartilage (necr otic scleritis) were the major ocular changes. Similarly, lysis of cep halic cartilage and immature bone, accompanied by pyogranulomatous inf lammation, usually progressing to fibrosis, were the most common lesio ns associated with the cranial changes in both the rainbow trout and A tlantic salmon. Routine histological staining, including special stain s, failed to reveal the presence of pathogens associated with these le sions. However, immunohistochemical staining of representative section s from all cases with rabbit anti-Flexibacter psychrophilus serum (ATC C 49510) demonstrated significant numbers of antigenically related bac teria within the leading edge of some of the scleral and cephalic oste ochondritic lesions. Axenic cultures of Flexibacter psychrophilus were recovered from the eye lesions of the rainbow trout, but it was not p ossible to reproduce ocular lesions experimentally However, mortality was produced following intramuscular injection of rainbow trout with b acteria.