"Whirling disease" is a disease of salmonids, the family of fish that includes trout, salmon, and whitefish. Whirling disease is caused by a microscopic parasite known as Myxobolus cerebralis and gets its name from the abnormal whirling or tail-chasing behavior exhibited by some infected fish. Other symptoms include a blackened tail and head or spinal deformities. Most species of salmonids are susceptible to whirling disease infection and, particularly in young fish, the disease can cause high mortality rates. Learn more about this disease from the Whirling Disease Initiative.