Recovery of an extremely proteolytic form of Serratia liquefaciens as a pathogen of Atlantic salmon, Salmo salar, in Scotland.

During 1988, heavy mortalities were observed in three discrete populations of Atlantic salmon in Scotland. From moribund and dead animals, dense pure culture growth of an extremely proteolytic bacterium was recovered, which did not correspond to the description of any of the validly described fish pathogens. The organism, which was initially considered to have characteristics intermediate between Aeromonas veronii and Serratia liquefaciens, was eventually equated with the latter, i.e. S. liquefaciens, after seeking the advice of the Centers for Disease Control, Atlanta, U.S.A. The pathogenicity mechanism appears to involve the production of proteolytic extracellular products.