Whirling Disease in Montana

Whirling disease is a parasitic infection that affects salmonid fishes (trout, salmon, char, whitefish, grayling). The disease is named for one of the symptoms of infection: erratic, tail chasing, “whirling” behavior. Infection can lead to physical deformities of the head, spine and cartilage and a blackening of the tail. Severe infection can lead to death as these deformities reduce a fish’s ability to feed and avoid predators. In some cases, whirling disease has caused major fishery losses and associated economic costs. There is no known cure or vaccine for whirling disease.

Fish with Whirling Disease. Photo courtesy State of Colorado

Whirling disease is caused by the microscopic parasite Myxobolus cerebralis, which was introduced from Europe to the US in 1956. The disease-causing parasite has a complex, two host life cycle that depends upon salmonid fishes and a small, common aquatic worm called Tubifex tubifex. Whirling disease cannot infect humans, mammals or non-salmonid fishes.

Tubiflex tubiflex.Photo courtesy The fish guide/div>

Whirling disease is spread through the movement of infected fish or fish parts, and by the movement of water or mud that contains parasites. This can happen naturally within a watershed, but the spread into new watersheds is typically done inadvertently by humans. Whirling disease was first discovered in Montana in 1994 and has spread throughout much of Western and Central Montana.


Combat Whirling Disease

  • Know whether you are fishing or recreating in waters infected by whirling disease. Whirling disease has been detected in most major watersheds of Western and Central Montana.
  • After leaving a stream or lake, be sure to thoroughly clean, drain and dry all of your fishing and boating equipment, including your waders. Mud and water may hold tubifex worms, whirling disease spores, and other invasive species.
  • Never transport live fish, live bait, insects or plants from one water body to another. It is illegal in Montana.
  • Don’t use salmonid (trout, char, salmon, whitefish, grayling) parts as cut bait. It is illegal.
  • Don’t collect sculpins or use them as bait. It is illegal.
  • When cleaning fish, either sink the entrails in the water body where the fish was caught or put them in garbage cans. Whirling disease may be able to survive wastewater treatment systems, so do not put fish parts down the kitchen disposal. Fish parts should be disposed of in the garbage, by burying, or by burning.
  • Talk to your friends and colleagues about this issue. Share what you know about whirling disease.
  • If you see fish with whirling disease symptoms in an area where whirling disease has not been reported, contact your regional Montana Fish, Wildlife & Parks office.


How Whirling Disease Infects Fish. Graphic courtesy New Mexico Department of Game and Fish. Getty Images.

Actions you can take to protect your local fishery

  • Obtain a copy of Montana Fishing Regulations and abide by them.
  • Become proficient at identifying different species of fish so that you don’t accidentally hurt endangered species.
  • Do not release any fish into your lake that were not caught there. IT IS ILLEGAL. Introduced species may out-compete native species for food and habitat, may introduce diseases, and may degrade water quality.
  • Keep sediments from entering streams, rivers and lakes. Sediments can smother lake spawning areas, aquatic plants and fish food such as crayfish, insects, etc.
  • Prevent nutrients and pollutants from getting into the lake by reducing your use of chemical fertilizers and maintaining your septic system.
  • Do not remove cover over the water such as trees, logs or aquatic plants. These materials provide critical habitat, protect bank stability and prevent rapid increase in water temperatures that harm cold-water fish.
  • Guard against the introduction of aquatic plants, invertebrates and fish species not naturally found in your lake.
  • Don’t leave cut fishing line in the water and clean up any line that you may find in the water.
  • When cleaning fish, either sink the entrails in the water body where the fish was caught, or put them in garbage cans.
  • Clean, drain & dry live wells, transom wells, and bilges thoroughly and away from any river, lake or water body.

Proliferative Kidney Disease in Yellowstone River

In August of 2016, water-based recreation was banned along a 183-mile stretch of the Yellowstone River and all of its tributaries to help limit the spread of a microscopic fish-killing parasite. Montana Fish, Wildlife and Parks enacted the closure from Yellowstone National Park’s northern boundary at Gardiner to the Highway 212 bridge in Laurel. The parasite causes Proliferative Kidney Disease (PKD) in fish, but does not pose a danger to humans. The disease is compounded by other conditions in the river such as low flow, consistent high temperatures, and the impact of recreational activities.

Although it has been found in only two isolated parts of Montana in the past 20 years, outbreaks have been documented in other northwestern states such as Washington, Oregon and Idaho. Regarding the closure and its impact to the recreational economy, Governor Steve Bullock said, “A threat to the health of Montana’s fish populations is a threat to Montana’s entire outdoor economy and the tens of thousands of jobs it sustains.”

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