We conducted laboratory evaluations of food consumption, growth, and metabolic rate as functions of water temperature (5–27.5°C) to examine how the young of year in six populations of muskellungeEsox masquinongy(Kentucky, Minnesota, New York, Ohio, St. Lawrence River, and Wisconsin) from three drainages might perform under various thermal regimes. Relative food consumption (g·g−1·d−1) and growth (g·g−1·d−1) were similar among populations at lower temperatures (5 and 10°C, but at higher temperatures (15–27.5°C) fish from Wisconsin and Ohio had higher consumption and faster growth rates than fish from Kentucky and the St. Lawrence River. Metabolic rates increased with temperature from 0.08 mg O2·g−1·h−1at 5°C to 0.25 mg O2·g−1·h−1at 25°C, but few differences in metabolic rates were observed among populations at any temperature. Although we found bioenergetic differences among muskellunge from these populations, they could not be explained solely in terms of thermal adaptation or previously defined genetic groupings. Energetic differences among age-0 muskellunge have important implications for conserving existing esocid populations and managing introduced populations.