Pathogenic Vibrios in Confinement-Reared and Feral Fishes of the Maine–New Hampshire Coast

Abstract

Vibrio anguillarum was isolated from moribund or fresh dead confinement-reared or feral fishes from the Maine–New Hampshire coast. All Vibrio isolates were tested for pathogenicity by inoculation into 12–15 cm-coho salmon (Oncorhynchus kisutch) smolts reared in fresh water. In 1975, of 35 isolates from confinement-reared fishes, 29 were Vibrio and 22 of these killed test fish; 1 of 4 isolates from feral fishes was a pathogenic Vibrio. In 1976, of 69 isolates from cultured fishes, 52 were Vibrio and 12 were pathogenic; 39 of 59 isolates from feral fishes were Vibrio, yet only 1 was pathogenic. One group of Vibrio isolates, all from winter flounder (Pseudopleuronectes americanus), killed all salmon smolts the same day of injection; one strain (569) consistently killed smolts within 3–4 h after inoculation. With microtiter methods, agglutinin titers of rabbit antisera were determined against all pathogenic V. anguillarum isolates. Three distinct antigenic groups of V. anguillarum, confirmed by agar-gel diffusion and challenge, were found on the Maine–New Hampshire coast. Although two of these groups appear to be antigenically similar to West Coast strains 775 and 1669, a third group shows little relationship to other East Coast–West Coast serotypes. Key words: Vibrio anguillarum, coho salmon, pathogenic Vibrio, confinement-reared (cultured) fishes, serotypes, agar-gel diffusion