Whirling disease in the Crowsnest River: an emerging threat to wild salmonids in Alberta

We provide the first documented case of whirling disease (WD) impacts to wild, self-sustaining rainbow trout (RNTR, Oncorynchus mykiss) populations in Canada. Myxobolus cerebralis (Mc), causative agent WD, was confirmed Alberta 2016. However, evidence local fish unknown. Using a weight-of-evidence approach, we examined multiple parasite life cycle stages Crowsnest River, Alberta. Percentage infected Tubifex tubifex worms actively shedding triactinomyxons (TAMs) exceeded known thresholds Mc establishment and TAM densities instream cause ?90% declines RNTR populations. detected at 5 6 study sites water, fish, worms. Disease severity highest lower watershed where 100% sentinel tested positive for 7 14 days post-exposure; up 85% wild fingerling showed clinical signs yearling were largely absent from river suggesting reduced survival. Our findings indicate conditions necessary outbreak WD exist Alberta, highlighting need consider this as an emerging threat salmonid