Groups of sexually mature yellow perch were held during the winter at constant temperatures of 4 and 6C for 123, 143, 164, 185, and 213 days, and of 8 and 1C for 157, 201, and 241 days. The winter temperatures were raised to 20C at a rate of 2C per week at the end of each duration. The greatest reproductive success occurred in the group exposed to 4C for 185 days at a median spawning temperature of 12C. High spawning temperatures were associated with shorter durations and lower reproductive success. Reproductive success was lower at maturation temperatures above 4C and at durations departing from 185 days.