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Learn more about whirling disease and teach other fishermen what you know. Practice clean angling and prevent the spread to unaffected waters.
What is whirling disease?
Whirling disease is a parasitic infection caused by the non-native microscopic parasite, Myxobolus cerebralis. Its common name comes from the characteristic swimming behavior that results from the disease. Affected fish suffer reduced mobility and fertility, posing a risk to population health. It attacks juvenile trout and salmon. Read more about the science of the disease. You can also download information about whirling disease and how to prevent its spread.

What fish species are affected?
Most salmonids (salmon, trout and whitefish) are susceptible to infection. Some rainbow and cutthroat trout appear to be more susceptible than other trout species. Brown trout become infected with the parasite, but do not usually exhibit signs of the clinical disease. Studies in Montana and at the University of California-Davis have demonstrated that grayling and bull trout are very resistant to infection. Other salmonids, such as mountain whitefish, are also at risk.

How is whirling disease transmitted?
Whirling disease is usually transmitted by infected fish and fish parts that carry the parasite. It may also be transmitted by birds and it is possible fishermen could carry the disease on fishing equipment. Regardless of whether a fish shows signs of the disease, infected fish release the parasite into the environment when they die, contaminating the drainage. Myxobolus cerebralis spores can live through drought and freezing for up to 30 years. Spores infect its alternate host, the worm Tubifex tubifex, where Myxobolus cerebralis develops into the form that can infect juvenile trout. Read more about the life cycle of the whirling disease parasite.
How can I prevent the spread of the disease?
See our guide to preventing the spread of whirling disease. You should never transport live fish, fish parts, animals or plants between water bodies. Always decontaminate fishing equipment when moving among drainages. Learn more about whirling disease and teach other anglers what you learn. Support TU's efforts to combat whirling disease by becoming a member today.

What is being done to fight whirling disease?
The Whirling Disease Foundation coordinates a national effort to combat whirling disease. Each year, the Whirling Disease Symposium brings scientists and anglers together to discuss the latest whirling disease research and plan future research priorities. Over 200 university, state agency and federal scientists are now conducting research on the problem.

Is there hope?
Yes. Just a few years ago, whirling disease had infected many of our finest trout streams, causing precipitous population declines in some. Little was known about the disease parasite, Myxobolus cerebralis, and its Tubifex tubifex worm host. Today, it's true that total eradication of the parasite is not likely, but recent studies by the nation's finest researchers point out real possibilities for management and control. For example:

  • A new commercially available water-filtering device that uses ultraviolet light can kill the whirling disease parasite in hatchery water sources and help control its spread.
  • Studies indicate that disease hotspots exist in rivers, and that some hotspots may be just a few feet wide. Knowing this, it may be possible to manage around or even clean up some of these hotspots, and increase the survival rate for nearby spawning trout.
  • A Montana study successfully imprinted wild trout eggs with a cold-water spawning temperature which may help the fry emerge earlier, thus avoiding the period of heavy infection.
  • In Colorado, a study is underway to filter the parasite from a heavily infected tributary, which may lower the mainstem infection.