Physiological and Behavioral Responses of Age-0 Muskellunge during Simulated Stocking in Elevated pH Water

Successful stocking of Muskellunge Esox masquinongy into reservoirs is hampered by a variety of stressors that can affect poststocking survival, such as elevated pH conditions common to eutrophic water bodies. We quantified Muskellunge survival, behavior, and physiological responses during a simulated stocking event where age-0 Muskellunge were netted, held on a hauling truck for 2 h, and then released into water with either the same pH (8.4) or one of two elevated pH levels (8.6 or 9.8). Following the hauling simulation, Muskellunge exhibited an upregulation of plasma-associated stress responses. Stocking into high-pH water did not cause mortality, but Muskellunge stocked into pH 9.8 showed signs of stress through ion imbalances and increased surfacing behavior. Four hours after stocking there were indications of recovery with reduced indicators of physiological stress, but Muskellunge did not fully recover in that time. Our study suggests that elevated pH alone may not result in short-term (≤4 h postrelease) poststocking mortality of age-0 Muskellunge but does add to the cumulative stress incurred during the stocking process.