FOUND IN B.C.? No
CURRENTLY KNOWN IN: Southern Alberta, including Bow, Old Man, Spray, Red Deer, North Saskatchewan and Crowsnest Rivers. Also present in Montana, Idaho and Washington (among other U.S. states).
Whirling disease is caused by an invasive, parasitic myxosporean called Myxobolus cerebralis. The parasite belongs to the phylum Cnidaria, so it is actually related to corals, anemones and jellyfish! It causes young salmonid fishes, including whitefish, trout and salmon species, to die prematurely.
As the name suggests, infected fish are often found swimming in an abnormal whirling pattern as the disease causes damage to the cartilage in the backbone. This is a reason why juvenile fish are more susceptible to the disease. Other common symptoms include a bent and darkened tail, deformed heads and bulging eyes.
M. cerebralis has a complex two-host life cycle that alternates between a worm (Tubifex tubifex) and a salmonid fish. First, an infective spore called a myxospore is released by an infected fish and is consumed by a T. tubifex worm, which prefer fine, soft sediments of lakes and rivers. Then, triactinomyxon spores (TAMs) are produced inside the T. tubifex worm. TAMs are released by the worms into the water until they can attach to the skin or gills of a fish. When an infected fish dies, myxospores are released back into the environment to begin the life cycle again.
Introduction and Spread
M. cerebralis is native to Europe. In the U.S., whirling disease has been present since the 1950’s and caused significant decreases in many salmonid populations. Whirling disease was first detected in Canada at Johnson Lake in Banff National Park in 2016 and has since spread across watersheds in southern Alberta. It is unclear how the disease was introduced to Canada, whether it was transmitted by wildlife or by angling gear from an infected location in the U.S.
Myxospores can remain alive for more than 20 years in the sediment covered beds of lakes and rivers. This is a reason why the spores are particularly persistent in felt-soled wading boots, which are a significant vector of spread of the disease. The disease is also able to spread naturally through the movement of fish carcasses by wildlife, such as eagles.
Deformities in young salmonids caused by whirling disease makes it difficult for them to feed and avoid predators, leading them to die prematurely. The large die-offs of younger salmonids ultimately affects the age structure of fish stocks and populations. These imbalances in fish age groups can lead to trophic cascades, a phenomenon that can be triggered by removing predators from an ecosystem, such as trout and salmon species. Subsequent imbalances develop in prey species, such as snails, insects and other microscopic plants and animals.
Although the parasite does not infect predators or humans that may consume infected fish, anglers and hunters are still impacted by whirling disease indirectly as the health of popular sportfish declines. In Montana and Colorado, some populations of rainbow trout declined by 90% after the disease was introduced. Some fish species are more susceptible to the disease: brown trout and coho salmon appear to be more resistant to the disease compared to rainbow trout and sockeye salmon, for example. Commercial and indigenous fisheries and hatcheries are also threatened by whirling disease.
There is no known cure for whirling diseases. Eradication of the disease is unlikely once it is established in a watershed.
For a summary of whirling disease and its effects, watch this short video.
What Can We Do?
CLEAN DRAIN DRY: Clean off all plant parts, animals and mud from watercraft and equipment (e.g. boat trailers, paddles, fishing gear, waders and boots). Drain onto land all compartments and accessories that can hold water (e.g. bilge, ballast, live wells, buckets) and remove plugs before traveling. Dry the watercraft and equipment before launching into another body of water.
INSPECTION: When travelling into B.C., all watercraft must be inspection and Watercraft Inspection and Decontamination stations. To learn more about what is required when bringing a boat to B.C. visit the Province of B.C.’s Invasive Mussel Website.
DON’T LET IT LOOSE: Be aware of bait restrictions in B.C. Never transport live fish, water, plants or sediments from one waterbody to another. Do not use trout, whitefish or salmon parts as cut bait. Never discard fish parts in or near streams and rivers. Dispose of unwanted bait, worms and fish parts in the trash.
Literature and Resources
Anlauf, K. J., & Moffitt, C. M. (2010). Modelling of landscape variables at multiple extents to predict fine sediments and suitable habitat forTubifex tubifexin a stream system. Freshwater Biology, 55(4), 794–805. https://doi.org/10.1111/j.1365-2427.2009.02323.x
Sarker, S., Kallert, D. M., Hedrick, R. P., & El-Matbouli, M. (2015). Whirling disease revisited: pathogenesis, parasite biology and disease intervention. Diseases of Aquatic Organisms, 114(2), 155–175. https://doi.org/10.3354/dao02856
Whelan, C. (2020). Distribution and habitat characteristics of Tubifex tubifex, intermediate host of whirling disease, in Banff National Park [MSc Thesis]. http://hdl.handle.net/1880/112571