Endangered Atlantic Whitefish (Coregonus huntsmani) retain high saltwater tolerance after generations of landlocking

Many fish populations that would normally migrate between fresh water and the ocean have become landlocked after river damming. To restore migration, these populations must retain the physiological capacity to tolerate ocean life, including high salinities. The Atlantic Whitefish (Coregonus huntsmani) is an endangered, ancestrally anadromous fish that now persists as a landlocked form in a single Canadian watershed. To assess the potential for restoring anadromy in this species as part of their recovery plan, we examined the effects of salinity on F1 captive-bred juveniles reared at 0, 15, and 30 ppt over 10 months. We measured growth, condition, and indicators of metabolism (blood glucose, lactate), osmoregulation (plasma osmolality), and stress (cortisol) in 13-month-old fish under cool (12 ± 2°C) and 16-month-old fish in warm (17 ± 2°C) conditions. Survival and seawater performance remained high across salinities, timepoints, and temperatures, with no indication of stress or osmoregulatory impairment. These results suggest Petite Rivière Atlantic Whitefish retain strong seawater tolerance, supporting the feasibility of re-establishing anadromy as part of recovery.