Standard metabolic rate of the pumpkinseed Lepomis gibbosus was estimated from measurements of routine oxygen consumption and random activity at acclimation temperatures of 8–32 C and within each season of the year. Routine and standard metabolic rates increased from winter (January-March) minima to spring (April-June) maxima, independently of acclimation temperature. For example, standard metabolic rate of a 100-g fish increased from 1.8, 3.0, and 4.8 mg O2˙hour−1at 8, 16, and 24 C, respectively, during winter, to 3.5, 5.6, and 9.2 mg O2˙hour−1at the same temperatures, respectively, during spring. The annual energy requirement for standard metabolism, derived from seasonal rate-temperature curves and a simulated annual temperature cycle at 44°N latitude, is 5.01 × 105joules. The annual cycle is anticipatory in that the increase in metabolic rate during spring begins independently of the vernal rise in environmental temperature. Depression of standard metabolism during fall and winter suggests an adaptive metabolic strategy similar to hibernation in endotherms. These findings provide a possible explanation for previously reported thermal zones of metabolic homeostasis in the pumpkinseed and other species, and illustrate the inadequacy of single-season calorimetric determinations for estimation of annual energy budgets in fish.