In the 1990s it looked like the Madison River fishery was doomed. Trout populations were down by as much as 90 percent due to whirling disease. Although over 150 rivers in the state have been infected, the Madison has now recovered significantly from this parasitic disease, thought to have originated in Europe, where brown trout have largely developed immunity to it.

The disease is caused by a parasite that infects the head and spine of fingerling trout, causing them to swim erratically. In addition to their whirling swimming, infected fish may have a darkened tail, twisted spine, and deformed head with a shortened and twisted jaw.

Although rainbow and cutthroat trout are most susceptible, the condition can affect any salmonid species.

Researchers have worked on ways to ameliorate the damage of whirling disease, including identifying resistant fish, and preventive measures have significantly helped prevent the spread of Myxobolus cerebralis, the protozoan spore that causes the illness.

Because there is no known cure for the disease, it is important that anglers follow these precautions:

Find more information on whirling disease online at www.whirling-disease.org.