An outbreak of vibriosis associated with high morbidity and mortality in a mixed population of marine fish occurred in an aquarium facility. No fewer than 12 species of fish were involved including one elasmobranch. Clinical signs were characterized by lethargy, occular opacity, and milky cloudiness of body surfaces. Occasionally this cloudiness was present in conjunction with actual pallor. These changes were followed by anorexia and a concurrent erythema on the fin bases and in the mouth. In those cases where the course of the condition was prolonged fin and body ulcers developed.

Gross lesions in early cases were limited to severe catarrhal branchitis with no evidence of accompanying changes in the body viscera. As the epizootic progressed, lesions involving kidney, liver, and spleen were observed, and recent cases exhibited severely distended small intestines containing epithelial casts. Histopathological observations from hematoxylin and eosin/phloxine stained sections revealed initially, either a diffuse chronic active branchitis or necrotizing branchitis with only a diffuse fatty change in the liver as the accompanying visceral change. Subsequent cases revealed in addition to the branchitis; pericholangitis, necrotizing hepatitis, splenitis, and interstitial nephritis. Though such changes were suggestive of a septicemia they were not in themselves typical of the pathology usually associated with Vibrio anguillarium.

Initial bacteriological isolates from early cases yielded only V. alginolyticus and only from gill specimens; no V. anguillarium was obtained from gill or visceral tissue samples. Subsequent cases yielded only V. anguillarium from gill, liver, and kidney tissues.

This report will present gross and histopathological changes observed, species distribution and organ distribution of observed lesions; as well as a discussion of the pathogenicity of the initial V. alginolyticus isolate.

We greatfully acknowledge the assistance of the Eastern Fish Disease Laboratory in confirming the vibrio species, and the National Aquarium of Baltimore for their patience in pursuing this problem.