Whirling disease

Anglers must do their part to keep from spreading whirling disease

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.

Fortunately, Myxobolus cerebralis, the parasite that causes whirling disease, does not infect people, and is not a risk to human health.

What is DWR doing to fight whirling disease?

In 1991, the DWR discovered whirling disease in Utah in a series of private hatcheries and adjacent waters in the Fremont river drainage of Wayne county. Initially, an attempt was made to eradicate the parasite by removing fish from those streams and reservoirs for an extended period of time. That effort proved unsuccessful and since then, the parasite has been found the in several private hatcheries, one state hatchery and waters in Cache, Weber, Beaver, San Juan, Summit and Sevier counties.

These and other discoveries have since refocused the DWR's efforts toward control and containment. In some areas, the DWR has installed barriers to prevent the spread of infected fish. The agency has closed state hatcheries near affected streams to visitors, except by appointment. State hatcheries are tested every 6–12 months to ensure they remain free of the parasite. Stocking policies have changed from the less-resistant rainbow trout to the more-resistant brown trout in contaminated stream.

The DWR's Aquatic Animal Health and Research Center continues to conduct ongoing research to determine the impacts whirling disease parasite on wild trout populations and ways to help prevent its spread. Part of this effort includes surveying new waters annually to determine the extent of the whirling disease parasite throughout the state.

In addition, DWR is initiating an education campaign with the help of Utah Trout Unlimited to educate the public about whirling disease. Signs on streams and lakes to alert anglers to the dangers of spreading the parasite, informational brochures and videos will all be part of the campaign.

What can you do to help prevent the spread of whirling disease?

DO clean all equipment such as boats, trailers, waders, boots, float tubes and fins of mud before leaving an area when fishing. Thoroughly dry equipment in the sun if possible before reuse. If you are traveling directly to other waters, clean your equipment with a 10 percent solution of chlorine bleach or use another set of equipment.

DON'T transport live fish between bodies of water. This practice could spread disease and is strictly illegal unless the fish have been completely tested free of disease.

DON'T dispose of fish heads, skeletons or entrails in any body of water. Fish parts should be disposed of in the garbage, by deep burying or by total burning.

CALL If you observe the symptoms of whirling disease in fish or observe illegal stocking. Contact your local conservation officer directly or call the poaching hotline at 800-662-3337.