Whirling disease is caused by Myxobolus cerebralis, a microscopic parasite that affects salmonid fish such as trout, salmon and whitefish. The parasite has 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 disease impacts 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%.
- Learn more about the life cycle and impacts caused by whirling disease.
Signs of infection
Fish infected with whirling disease may show the following signs:
- A '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.
Whirling disease in Alberta
Whirling disease has been detected in a number of waterbodies in 4 major watersheds in central and southern Alberta:
- Bow River
- North Saskatchewan River
- Oldman River
- Red Deer River
View the maps of where whirling disease has been detected in Alberta:
- Map: Where is Whirling Disease in Alberta?
- Canadian Food Inspection Agency: Map of Declared Areas for Finfish Reportable Disease Declarations for Alberta
- Canadian Food Inspection Agency: Finfish Reportable Disease Declarations for Alberta
Learn more about whirling disease:
August 29: Alberta Environment and Parks (AEP) staff detected clinical signs of whirling disease in rainbow trout and mountain whitefish populations in the Crowsnest area.
March 9: The CFIA declares the North Saskatchewan River watershed infected with whirling disease.
June 23: The CFIA declares the Red Deer River watershed infected with whirling disease.
May 1: The CFIA declares the Oldman River watershed infected with whirling disease.
February 10: The CFIA declares the Bow River watershed infected with whirling disease.
August 23: Testing conducted in Alberta by the CFIA confirms the presence of whirling disease in Johnson Lake in Banff National Park.
Whirling disease makes a resurgence in the United States, 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.
Whirling disease is found mostly in fish hatcheries in the northeastern United States.
Whirling disease is first observed in the United States.
The Whirling Disease Program provides annual reports highlighting the program year and the priorities for the upcoming year.
Responses to whirling disease
AEP and the CFIA are developing long-term detection and surveillance plans to protect Alberta’s trout and whitefish fisheries as much as possible.
- Information on whirling disease, how it impacts fish populations, Alberta's action plan and tips for anglers to help stop the spread.
In 2016, AEP issued Ministerial Order 52/2016: Fish Quarantine 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 reduces the risk of whirling disease transmission from fish farms and hatcheries to wild populations, and helps protect Alberta’s fish populations and world-renowned fishing industry.
The 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.
Crowsnest River Project
In 2019, AEP staff conducted a sentinel cage study to determine the extent and impacts of whirling disease within the Crowsnest River. Several cages, containing uninfected rainbow trout, were installed on the Crowsnest and Oldman River. These fish were tested to determine the severity of whirling disease in the river.
The Government of Alberta has developed a Decontamination Protocol for Watercraft and Equipment. If you participate in water-based outdoor recreation such as angling or boating, or you work around waterbodies, you can help prevent the spread of whirling disease. To review the protocol and its support documents, see the Stop the spread of whirling disease page.
Learn more about how you can prevent the spread of whirling disease: