Last modified: Monday, March 06, 2017
Fisheries Experiment Station

Home | Administration | Research | Culture | Fish health | Ichthyogram | Contact FES

Fish health > Yellow grubs | Fungused brown trout | Approval | Whirling disease

Whirling disease in Utah

Whirling Disease is a condition affecting trout and salmon caused by a microscopic parasite known as Myxobolus cerebralis. The parasite attacks the cartilage tissue of a fish's head and spine. If sufficiently infected, young fish may develop symptoms such as whirling behavior, a black tail or even death. If they survive, fish may develop head deformities or twisted spines.


Scientists believe there are other harmful effects such as making fish more susceptible to predation, less able to feed, to survive environmental disturbances or to reproduce. Recently, fisheries researchers have initiated long-term whirling disease impact studies, but no definitive conclusions have been made. However, population collapses in famous rainbow trout rivers such as the Madison and Colorado have caused experts to reassess the parasite's impact.

The parasite goes through a complex life cycle that includes tiny aquatic worms which are found in most waters. These host worms, which become infected, release a fragile stage of the parasite that must infect a trout within a few days or perish. Infected trout develop very persistent spores which can survive in moist environments for years. When an infected fish dies and decomposes, the spores are released into the environment and can survive transit through a predator's digestive tract or could be transferred on muddy boots or other equipment.

Among species found in Utah, rainbow trout are the most susceptible, followed by kokanee salmon, golden, cutthroat, brook, brown trout and splake. Recent discoveries show whitefish may be infected as well. Lake trout may be infected under laboratory conditions and other game fish species such as bass, bluegill, perch or walleye do not get whirling disease.

Note: the parasite DOES NOT infect human beings.

More on whirling disease