1983 Volume 49 Issue 1 Pages 61-67
The rose bitterling (Rhodeus ocellatus ocellatus, Cyprinidae), a spring and summer breeder, was exposed to various temperature and photoperiod regimes during the different phases of the annual reproductive cycle. In early spring, warm temperature stimulated the recrudescence of the gonads regardless of photoperiod. But during late summer and autumn, a long photoperiod was required to maintain or initiate the gonadal maturation especially at high temperatures (22-28°C). These results indicate that the initiating factor of the breeding season in this species is a rising temperature, whereas the terminating one is the decreasing daylength at high temperatures. Therefore, in the rose bitterling, the responsiveness of the gonads to photoperiod varies clearly with season. The critical photoperiod for maturation falls between 13 and 14hours of light per day. This critical photoperiod could be changed by a pretreatment of artificial photoperiod during the breeding season.