Photoperiod and temperature are two environmental factors that have significant effects on fish physiology and behavior but few studies have investigated the effect of photoperiod on swimming performance. We studied the effects of five photoperiods, designated 24L:OD (24 h light:0 h dark), 16L:81), 12L: 12D, 8L: 16D, 0L:241), and three temperatures (5, 15, and 25°C) on the swimming performance of white crappiePomoxis annularis(5–11 cm in standard length) in a swim tunnel with propeller-driven flow. Two-factor analysis of variance (alpha = 0.05) indicated that both photoperiod and temperature significantly affected fish swimming performance but the interaction of photoperiod and temperature did not. At all temperatures, the 8L: 16D photoperiod resulted in the highest mean swimming speeds. In addition, the temperature effect was consistent at all photoperiods. The mean swimming speed at 5°C was significantly slower than at 15°C or 25°C; however there was no significant difference between swimming speeds at 15°C and 25°C. Our documentation of a photoperiod effect on fish provide further confirmation of the importance of this environmental variable on swimming performance.