EXAMINATION OF GILLS FROM SALMONIDS WITH BACTERIAL GILL DISEASE USINGMONOCLONAL-ANTIBODY PROBES FOR FLAVOBACTERIUM-BRANCHIOPHILUM AND CYTOPHAGA-COLUMNARIS

Bacterial diseases of the gills of commercially reared salmonids in fr eshwater are common problems. They accounted for 18% of all diagnostic submissions to the Atlantic Veterinary College from commercial fish h atcheries. Definitive diagnosis is difficult because of the growth cha racteristics of the putative bacteria in culture. Research into the pa thogenesis of these diseases has also been similarly limited. Monoclon al antibodies (MAbs) were developed to 2 globally significant gill bac terial pathogens, Flavobacterium branchiophilum, the causative agent o f bacterial gill disease, and Cytophaga columnaris, the causative agen t of columnaris disease of salmonids. These MAbs were then used as the basis for an indirect fluorescent antibody test to assess archived ca ses of gill disease in our region. Flavobacterium branchiophilum was t he dominant bacterium detected in the biofilm of diseased gills in our study region. Of the cases tentatively diagnosed based on histopathol ogy as bacterial gill disease, 76.2% tested positively with the MAbs t o F. branchiophilum. Also present within 18.7% of these cases were bac teria which reacted positively to the MAbs for C. columnaris. We concl ude that the MAbs produced are valuable diagnostic and research probes for common bacterial diseases of the gills of salmon and trout in Atl antic Canada. This study also adds further proof that F. branchiophilu m acting alone can be sufficient cause for bacterial gill disease.