Yersinia ruckeri is the causative agent of yersiniosis or enteric redmouth disease (ERM) and causes significant losses in salmonid aquaculture worldwide. Although infection with this agent has been reported in other fish species, salmonids and especially rainbow trout are most susceptible to ERM. Vaccination of fish with a commercial Y. ruckeri bacterin provides good levels of protection, however, disease outbreaks do occur from time to time. ...