Photo credit: Sascha Hallet & FishPathogens.net
ID Characteristics
General:
- Whirling disease affects juvenile salmonid fish, like salmon, trout and whitefish. It is caused by a parasite carried by a freshwater worm.
- Once it has invaded a fish host, the parasite targets the head, spinal cartilage and nervous tissue.
Symptoms:
Whirling disease alters the affected fish’s brain stem and spinal cord, resulting in erratic ‘whirling’ swimming patterns.
Fish infected with whirling disease may exhibit the following characteristics:
- blackened tail
- deformed or bent tail
- skull deformities
- bulging eyes
However, fish may be infected with the parasite without showing external signs, so these deformities do not constitute proof of infection.
Origin
Whirling disease is native to Europe. It was introduced to Pennsylvania in the 1950’s. In 2023, whirling disease was detected in BC (in Yoho and Kootenay national parks).
How it Spreads
Whirling disease is caused by a parasite (Myxobolus cerebralis) that has two hosts as part of its life cycle: juvenile salmonids (such as salmon, trout, and whitefish), and a bottom-dwelling freshwater worm (Tubifex tubifex).
Infected Tubifex worms release Myxobolus parasite spores into the water, which infect salmonid fish through their skin. Fish can also become infected after eating infected worms. After the fish die, spores are released into the water to seek out Tubifex worms to repeat the cycle.
The movement of infected fish, mud or water can spread whirling disease. The parasite spores can hitchhike on gear used for swimming, paddling, boating, water pumping, or fishing. Felt-soled waders pose a particular risk. Lastly, infected fish (alive or dead) can spread the parasite spores, as can fish parts.
Impacts
Ecological:
- Whirling disease causes high mortality in fish populations, with as much as 90% die-off observed in some locations.
- It impacts salmonid population resiliency.
Economic:
- Whirling diseases lead to the closure of waterbodies for recreational use.
- It negatively impacts fisheries and hatcheries.
Prevent the Spread
Whirling disease is NOT currently found in the Sea to Sky Region, so PREVENTION is key:
- Clean, drain and dry your boat, trailer and other equipment before moving it to a new water body. This prevents the transport of the Myxobolus parasite spores between lakes and rivers.
- Clean: Remove plant fragments, aquatic species, and mud from any watercraft or equipment (boots, waders, fishing gear). Use hot water if possible.
- Drain: Drain all items that can hold water onto land (e.g., buckets, bait water, wells, ballast, and bilge). Do so away from storm drains, ditches, and waterways.
- Dry: Make sure all items are completely dry before entering a new water body.
- Don’t let it loose: Whirling disease has been observed in aquarium fish, so avoid disposing of unwanted fish into water bodies.
- Do not use felt-soled waders, or clean them with a cleansing detergent between uses.
- Never move fish or fish parts between water bodies.
- Dispose of fish parts in the garbage; do not dispose of fish or fish parts down the drain
- Bathe pets before allowing them to enter a new water body.
There is no cure for whirling disease.
Eradication is highly unlikely once the disease is established in a watershed.
Distribution of whirling disease in BC
Whirling Disease Factsheet
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