Abstract

Infections in marine cultured Pacific salmon (genus Oncorhynchus) and trout (genus Salmo) can include those caused by two bacterial pathogens. Vibrio anguillarum (vibriosis) and Aeromonas salmonicida (furunculosis). In the Puget Sound area, two distinct serotypes of V.anguillarum have caused extensive mortalities in net-pen culture. Although furunculosis is probably carried by fish from fresh water, it can be transmitted in seawater, and in the close confines of net-pen culture can reach epizootic proportions. In large-scale experiments, epizootics of vibriosis and furunculosis reduced the population of two sea cages (300,000) of chinook salmon by 80% during approximately 5 months of marine culture. Laboratory tests of the bacterial pathogen isolated from moribund fish indicated that the furunculosis organisms was resistant to oxytetracycline and sulfa drugs, but was sensitive to furazolidone. Multiple infections of both diseases proved difficult to treat. The results of these experiments indicate the need for better management of furunculosis during the freshwater culture stages of salmon.