US Fish & Wildlife Service


Date of this Version



UNITED STATES DEPARTMENT OF THE INTERIOR Fish and Wildlife Service Division of Fishery Research Washington, D. C. 20240


Enteric redmouth disease (ERM) is a systemic bacterial infection of fishes, but is principally known for its occurrence in rainbow trout, Salmo gairdneri. The disease was first reported in the 1950's by Rucker (1966), and in recognition of that fact, the causal organism was named Yersinia ruckeri by Ewing et al. (1978). Although Wagner and Perkins (1952) described a bacterial disease that produced a red-mouth condition in rainbow trout in California and Colorado, it was caused by a different bacterium; they isolated Pseudomonas hydrophila rather than Y. ruckeri.