Yersinia ruckeri, the enteric redmouth (ERM) bacterium, has been isolated from salmonid fish in Ontario and British Columbia on 16 occasions between 1982 and 1985. The 2 most common serovars, I and II, were found in both provinces. In 2 cases in British Columbia and 1 in Ontario, the isolates belonged to serovar V. This variety of Y. ruckeri has been found only once before, in Colorado fish. A serovar III isolate from British Columbia and a new serological variety (serovar VI) from Ontario have also been confirmed as Y. ruckeri isolates. The relative importance of these various isolates as disease agents is not clear, and, because of this, they present a problem when fish health management decisions must be made.