Whirling Disease

About Whirling Disease (Myxobolus cerebralis)

Whirling disease is caused by Myxobolus cerebralis, a microscopic parasite of salmonid fish, including trout, salmon and whitefish. The organism possesses a complex lifecycle that requires a salmonid fish and an aquatic-worm, Tubifex tubifex, as hosts.

Species such as rainbow trout, cutthroat trout and whitefish are particularly susceptible to whirling disease, though impacts of the disease differ among salmonid fish species and in different waterbodies.

The severity of whirling disease depends largely on the age and size of the salmonid host. Young fish are most vulnerable, with mortality rates reaching up to 90 per cent.

Where is whirling disease in Alberta?

Clinical Signs

Fish infected with whirling disease may exhibit any of the following observed signs:

  • A marked "whirling" swimming behaviour may be observed as the parasite invades cartilage and impairs the nervous system
  • Changes in physical appearance including:
    • Skeletal deformities of the body or head. This occurs when the cartilage of the spine or head is infected at a young age; the tail may be crooked and head cartilage sunken to show a sloped head.
    • Colour changes due to nerve compression, so that the tail may appear dark or even black.

Whirling disease is not harmful to humans or other mammals.

For further information about whirling disease, visit the Canadian Food Inspection Agency (CFIA) website at:

Whirling Disease Timeline

Whirling disease was first observed in the United States in the 1950s, and by the 1960s was found mostly in hatcheries in the northeastern states.

In the 1990s, the disease made a resurgence, particularly in the intermountain west, including Utah, Idaho, Colorado and Montana. In Montana, it was detected in depleted wild rainbow trout populations.

Whirling disease has been detected in 25 states in the US, although it is not necessarily established in each state. It remains particularly prevalent in western and northeastern areas of the country.

On August 23, 2016, testing conducted in Alberta by the Canadian Food Inspection Agency (CFIA) confirmed the presence of whirling disease in Johnson Lake in Banff National Park.

On February 10, 2017, the CFIA declared the Bow River watershed infected with whirling disease.

On May 1, 2017, the CFIA declared the Oldman River watershed infected with whirling disease.

On June 23, 2017, the CFIA declared the Red Deer River watershed infected with whirling disease.

On March 9, 2018, the CFIA declared the North Saskatchewan River watershed infected with whirling disease. The remainder of the province of Alberta is considered a buffer zone.

For further information visit the CFIA website at:

Response to Whirling Disease

Alberta Environment and Parks (AEP), in conjunction with CFIA, is developing longer term detection and surveillance plans to enable the protection of our trout and whitefish fisheries to the maximum extent possible.

Video: Alberta’s Whirling Disease Program

Decontamination Protocol

The Government of Alberta has developed a Decontamination Protocol for Watercraft and Equipment, along with the following support documents:

  • Decontamination Equipment List
  • Decontamination Quick Reference List
  • Decontamination Risk Map

To access these documents, see:

Fish Quarantine

AEP issued a Ministerial Order to quarantine all commercial fish culture operations until individual fish farms and hatcheries licensed for salmonids are tested for the presence of whirling disease.

The precautionary quarantine of fish farms and hatcheries will help protect Alberta’s fish populations and world-renowned fishing industry by reducing the risk of whirling disease transmission from fish farms and hatcheries to wild populations.

The precautionary quarantine will be in place until each facility has tested negative free of for whirling disease. Fish farms may resume stocking once they are confirmed to be free of the disease.

What You Can Do

If you participate in angling, boating or other water-based outdoor recreation, or you are employed in aquatic research or other work around waterbodies, you can help prevent the spread of whirling disease.


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Updated: May 22, 2018