EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON THE SPAWNING OF YELLOW PERCH (Perca flavescens)1

Abstract

ABSTRACTThe yellow perch (Perca flavescens) in Lake Mendota, Dane County, Wisconsin, normally spawn over a 2‐ to 3‐week period in April to early May when the water temperature reaches 8.0 to 12.0°C. Adult fish captured and warmed from 2.5 to 9.0–13.0°C in February began spawning in the laboratory within the same 4‐day period in April as did the fish in Lake Mendota. This was true regardless of whether the perch in the laboratory were under a 13.5‐hour light (L)/10.5‐hour dark (D) or a 10.5 L/13.5 D photoperiod. The spawning season in the laboratory, however, lasted 2 weeks longer than it did in the field. Perch captured in April spawned readily (within 7 days) in tanks under a 13.5 L/10.5 D photoperiod when the temperature was raised from 5.0 to 12.0°C. Perch also spawned under photoperiods of 18 L/6 D and 6 L/18 D when warmed from 5.0 to 12.0°C, but the predictability of spawning was decreased. Keeping fish at 5.0°C slowed but did not entirely prevent the onset of spawning. In separate tests, the proportion of females that spawned within 7 days of a 5.0 to 12.0°C temperature shift increased as the spawning season progressed. It is concluded that the onset of spawning in yellow perch depends more on the intrinsic maturational state of the gonads than on specific spring‐time photoperiod‐temperature cues. Temperature may exert a major influence on maturation and seems to have a modulating influence on spawning. However, rising temperature and/or temperature thresholds per se do not determine when perch spawning begins. Photoperiod may also have a modulating influence on spawning, but one that is not as important as that of temperature.