Bow River watershed infected with fish parasitic disease

Testing has found whirling disease throughout the Bow River and its tributaries as well as commercial aquaculture sites

LACOMBE, Alta. — Alberta’s Bow River watershed has been declared infected with whirling disease, a parasitic infection affecting trout, salmon and whitefish.


The Canadian Food Inspection Agency and Alberta Environment are working on long-term surveillance of wild fish and aquaculture facilities. 


Commercial facilities will have to test fish for the disease and implement approved biosecurity in order to obtain a CFIA permit to stock fish from the infected areas.


Young fish are most vulnerable, and up to 90 percent may die of the disease. 


Some exhibit a whirling swimming pattern, a black tail, spinal curvature and sloped nose compared to a normal fish, said Bev Larson of Alberta Fish and Wildlife.


Laboratory testing is needed to confirm the disease. 


It was first found in Germany about 100 years ago and spread to the United States in the 1960s. It appeared in Montana in 1995. 


“It was thought to be more of a hatchery disease,” she told the Alberta Invasive Species annual meeting in Lacombe March 23.


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“There didn’t seem to be problems in the wild.” 


A microscopic parasite called Myxobolus cerebralis is responsible. It involves multiple stages of the parasite and requires two hosts starting with an aquatic worm and then invasion of the fish through the skin. Spores travel via the nerves to cartilage and bone. 


Alberta started conducting surveillance in 1997 in the Oldman, Bow and Red Deer rivers, where wild fish as well as hatcheries were checked. 


Last summer it was found in a lake in Banff National Park.


Further testing found it throughout the Bow River and its tributaries as well as commercial facilities. Nine private fish facilities tested negative, but five were positive so they are in quarantine while the CFIA conducts trace-outs covering the last three years.


Surveillance has also looked at the Athabasca, Red Deer, North Saskatchewan and Peace rivers.


No one is sure where it came from or when it invaded, said Larson. 


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Infected fish can be carriers as well as mud, water and equipment. 


“Dead fish have more potential spores than infected equipment,” she said. 


“Birds and animals can eat the fish and defecate elsewhere and the spore can withstand that.”


Water temperature, stream flow and age of fish are considered when tracking the disease. 


“A lot of factors have to come together that actually establish whirling disease,” she said. 


It does not harm wildlife or humans eating the fish. 


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