Metabolic scaling in a freshwater predator is robust across wild and hatchery-reared populations and experimental...

Standard metabolic rate (SMR) and maximum metabolic rate (MMR) define the energetic limits of aerobic metabolism in fishes and are increasingly recognized as flexible traits linked to life history variation. Yet the factors driving intraspecific variation in how SMR and MMR scale with body mass and temperature remain unresolved. We assessed mass- and temperature-scaling relationships in SMR, MMR and aerobic scope of walleye (Sander vitreus) using data from multiple intermittent-flow respirometry experiments conducted from 2020 to 2025. The dataset included wild fish from Lake Erie, Lake Ontario, and Rice Lake, and hatchery-reared individuals of Lake Ontario origin (n = 207). Additional MMR_Swim estimates from swim tunnel respirometry (n = 33) were compared with MMR_Recovery estimates obtained from a chase and air exposure protocol. Together, body mass and temperature explained 94.7% of the variation in SMR and 80.2% of variation in MMR across the 1-24.5°C range. Sex effects on SMR and MMR were negligible, and apparent differences between populations largely reflected differences in temperature ranges sampled rather than intrinsic population-level differences. Among wild fish (0.36-3.74 kg), SMR scaled hypoallometrically (b = 0.919), whereas hatchery fish, which were relatively smaller, were slightly hyperallometric (b = 1.081). Mass scaling of MMR_Recovery was shallower (b = 0.664) and consistent with MMR_Swim (b = 0.682). Our findings suggest that metabolic scaling in walleye is largely conserved across populations in the Laurentian Great Lakes, supporting single-population estimates for regional-scale bioenergetics models used to predict consumption and growth under climate warming.