One-year-old bay scallops, Argopecten irradians irradians (58±2 mm, 22±1 g live weight) were exposed to four replicated photoperiod treatments (24D, 8L:16D, 16L:8D, and 24L where D=dark hours, L=light hours) in order to measure the effect on gonad weight and maturation during the conditioning process.Results indicated that day-lengths of more than 8 h are necessary to promote gonad maturation in bay scallops.After 6 wk, the mean gonad weight for scallops in the 16-h and 24-h light regimes was similar at 0.6±0.1 g dry weight compared to a mean of 0.2±0.1 g dry weight for those in the 8-h and 0-h light regimes.