, a metazoan parasite with a two host life cycle (fish and aquatic Tubifex worms) can cause a serious affliction in some species of trout and salmon called whirling disease. See a fact sheet
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Trout can become infected when they encounter waterborne spores of the parasite, called triactinomyxons (TAMs). Severely infected young trout often develop debilitating deformities of the skull and spinal column. In some areas of Colorado, most of the young wild rainbow trout die 3 – 6 months after infection.
Colorado Parks and Wildlife researchers have determined that rainbow trout, brook trout, and all of Colorado’s native subspecies of cutthroat trout are quite susceptible to whirling disease if exposed when young. Because Colorado’s native cutthroats are susceptible, it is important to establish policies and personal habits that protect high country waters from the spread of the parasite (see “How You Can Help” on the Whirling Disease and Colorado's Trout page).
Although the effects of whirling disease in Colorado are still apparent particularly in reduced rainbow trout numbers in many waters, significant strides have been made in recent years in controlling the further spread of the parasite and the disease it can cause. These efforts include capital investments to protect the State’s hatchery system. In 1998, 11 of Colorado’s 16 hatcheries were contaminated by the parasite; in December 2004 just 6 are still considered positive for the parasite. CPW policy now dictates that no fish reared in a parasite-positive facility may be planted in waters capable of sustaining wild trout populations unless an exemption is obtained. Efforts such as these have resulted in a reduction in the density of the TAMs researchers detect in the wild in many of our waters. In some places, young-of-the-year rainbow trout are again being observed in the fall of the year. However, there is still progress to be made.
Current research topics regarding Myxobolus cerebralis include the following: