What is Whirling Disease and what fish are affected?
Whirling disease is a parasitic infection caused by the microscopic parasite, Myxobolus cerebralis. The disease is named for the characteristic swimming behavior that results as the parasite multiplies in the head and spinal cartilage of the infected fish. It attacks juvenile trout and salmon, but does not infect warm water species. All species of trout and salmon may be susceptible to whirling disease, and other members of the trout and salmon family, such as mountain whitefish are also at risk. Rainbow trout and cutthroat trout appear to be more susceptible than other trout species. Brown trout become infected with the parasite, but they appear to have an immunity to the infection and have not been as greatly impacted as rainbow trout. Studies in Montana and at the University of California-Davis have demonstrated that grayling and bull trout are very resistant to infection.

For more information on whirling disease and how you can help prevent its spread visit Trout Unlimited's Whirling Disease Web site or the Protect Your Waters: Whirling Disease Web site.