Growth and food conversion efficiency of hybrid bass juveniles (female striped bassMorone saxatilis× male white bassM. chrysops) were measured as a function of diel oscillating and constant temperatures, spring (increasing day length) and autumnal (decreasing day length) photoperiods, and ration sizes ranging from no food to daily satiation. The optimum temperatures for growth and peak conversion efficiency were estimated to be 26.8 and 21.2°C, respectively, for fish under constant temperatures, 12 h of daylight, and a maximum ration size. Springtime photoperiod significantly increased growth, and autumnal photoperiod significantly reduced growth. There was a significant temperature-photoperiod interaction; maximum growth occurred at 27.9°C under the springtime photoperiod and at 25.7°C under the autumnal photoperiod. Diel temperature oscillations with an amplitude of ±4, 6, and 8°C did not influence growth rate or conversion efficiency. Reduced ration sizes led to a lower optimum temperature for growth. Manipulation of temperature and photoperiod may be advantageous where feasible in intensive culture of hybrid bass. In field situations, stocking hybrid bass, a temperate eurytherm, may be successful where stocking striped bass, a temperate mesotherm, has failed because of thermal restrictions.