Energy reserves are important in determining reproductive behavior in many species. In fishes, mature males vary greatly in size and larger individuals have lower metabolic rates and higher energy reserves. Male smallmouth bass, Micropterus dolomieu, invest significant energy into parental care. In northern populations, where adults do not forage over the winter and rely on pre-existing energy reserves, adult males must recoup winter energy losses before initiating reproduction. However, males also exhibit territorial behavior, defending their nesting site from other male competitors before reproduction. We used a 10-year dataset to test the hypothesis that energetic allometry, rather than competition, controls seasonal reproductive timing by male M. dolomieu of different sizes. We found that larger males required fewer degree days (a measure of thermal energy experienced) before reproducing each year, which is consistent with the energetics hypothesis. Also, timing of peak reproduction was negatively related to the number of degree days accumulated early in a breeding season. Lastly, we found that changes in measures of growth between seasons better predicted changes in timing of reproductive behavior by males that spawned in two consecutive seasons than changes in measures of competitive ability. Together, these results suggest that timing of reproduction in this population is more strongly influenced by energetic constraints than competition.