Pathogenicity of Vibrio anguillarum for Juvenile Winter Flounder, Pseudopleuronectes americanus

Abstract

The pathogenicity of V. anguillarum for juvenile winter flounder, P. americanus, was quantitatively established under laboratory conditions. Fish were obtained from Rhode Island, USA, waters, acclimatized in tanks for 4-6 wk, and then challenged with V. anguillarum. The LD50 was relatively constant for 24-72 h cultures of the organism using i.p., i.m. and i.v. challenge routes. The LD50 via oral inoculation was about 3 logs greater. The LD50 for fish collected, acclimatized and challenged during the winter was .apprx. 3 logs less than that found for fish in the summer. The median i.m. LD50 for 11 strains examined under the optimum conditions for infection was 2.4 .times. 105 (range 7.3 .times. 104-1.6 .times. 106) organisms. Gross and histopathological changes in the acute form of the disease were minimal, being limited to anemia, leukopenia, ecchymosis and necrosis at the site of inoculation and behavioral changes. A chronic form of vibriosis was observed primarily during the summer in fish given sublethal doses. A potent, lethal V. anguillarum toxin was not demonstrated. Potentially, this reproducible host-parasite system might have use in a short-term bioassay procedure for toxic pollutants of the marine environment.