Enteric Redmouth

Enteric Redmouth (ERM) is also known as Hagerman redmouth disease, redmouth or salmonid blood spot. It produces a systemic bacterial infection and it primarily infects hatchery-raised rainbow trout.

The disease was first detected in the 1950's in farmed rainbow trout in the Hagerman Valley of Idaho.

ERM is responsible for severe hemorrhagic infections in hatchery-raised salmonids (salmon and trout) throughout Canada and the United States. Non-salmonid fish such as emerald dace, goldfish, carp and lake herring have been reported to harbor the pathogen.

The bacterium that causes ERM is Yersinia ruckeri.

Outbreaks of Yersinia ruckeri can occur when susceptible fish are subjected to stressful situations. There are no reports of outbreaks of ERM among wild populations of fish. Transmission of ERM can occur by direct fish to fish contact or by exposure of susceptible fish to waterborne bacteria.

Yersinia ruckeri commonly causes sustained, low-level mortality that may eventually result in heavy losses. In the early stages of an outbreak, affected fish become darkened and lethargic. Fish refuse food and appear to isolate themselves from other fish. Affected fish often are missing eyes, have "pop-eyed" or protruding eyes, are blind in one or both eyes and drift listlessly at the water surface. In the final stages of the disease, hemorrhages appear in and around the gum line of the mouth and on the tongue, giving the area an inflamed, reddish appearance.

ERM can be controlled by use of anti-microbial compounds, vaccines, and the use of disease-resistant fish.