The attachment of Vibrio pathogens to cells of rainbow trout, Oncorhynchus mykiss (Walbaum), was studied by use of species-specific monoclonal antibodies and indirect FITCimmunofluorescence microscopy. Vibrio anguillarum, V. ordalii and V. parahaemolyticus attached to cultured cells of rainbow trout gonads, various tissues of cryostat sections of whole fish, and smears of gills, intestine, buccal mucosa and skin. The attachment was inhibited by prior incubation of bacteria with monoclonal antibodies at titres of 1:32, or less. Other Vibrio pathogens used in this study did not attach to any trout eclls. The researeh provides approaches to study the mechanisms of bacterial attachment in the onset of Vibrio infections.

. A library of monoclonal antibodies has been developed for use in rapid diagnosis of Vibrio infecftions. It covers the Vibrio Species that are regarded as the major fish and shellfish pathogens, many of which are also human pathogens. Blind tests confirm the accurary of the monoclonals as a diagnostic test. Conjugation of enzyme lable onto the monoclonals is providing rapid identification of Vibrio species by use of direct, rather than indirect, immunological testing.

A virulent strain of Aeromonas hydrophila associated with epizootic ulcerative syndrome (EUS) was used to produce monoclonal antibodies that identified virulent strains of A. hydrophila. Antibodies from a clone, designated as F26P5C8, were found to identify the A. hydrophila serotype I isolates associated with EUS fish, and which were found to be virulent after subsequent inoculation studies. Immunodiagnosis of a large number of A. hydrophila from Australia and Japan showed some additional isolates to be identified by F26P5C8, but the status of their virulence is presently unknown.