Examination of Gills from Salmonids with Bacterial Gill Disease using Monoclonal Antibody Probes for Flavobacterium Branchiophilum and Cytophaga Columnaris

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Abstract
Bacterial diseases of the gills of commercially reared salmonids in freshwater are common problems. They accounted for 18% of all diagnostic submissions to the Atlantic Veterinary College from commercial fish hatcheries. Definitive diagnosis is difficult because of the growth characteristics of the putative bacteria in culture. Research into the pathogenesis of these diseases has also been similarly limited. Monoclonal antibodies (MAbs) were developed to 2 globally significant gill bacterial pathogens, Flavobacterium branchiophilum, the causative agent of bacterial gill disease, and Cytophaga columnaris, the causative agent of columnar-is disease of salmonids. These MAbs were then used as the basis for an indirect fluorescent antibody test to assess archived cases of gill disease in our region. Flavobacterium branchiophilum was the dominant bacterium detected in the biofilm of diseased gills in our study region. Of the cases tentatively diagnosed based on histopathology as bacterial gill disease, 76.2% tested positively with the MAbs to F. branchiophilum. Also present within 18.7% of these cases were bacteria which reacted positively to the MAbs for C. columnaris. We conclude that the MAbs produced are valuable diagnostic and research probes for common bacterial diseases of the gills of salmon and trout in Atlantic Canada. This study also adds further proof that F. branchiophilum acting alone can be sufficient cause for bacterial gill disease.