Effects of water temperature and photoperiod on the initiation and termination of the autumn spawning season in tobinumeri-dragonet Repomucenus beniteguri

In order to investigate the factors which initiate the autumn spawning, immature fish were reared under different conditions from August 15 to September 12. Spawning was observed from August 27 in the 12L12D/22-24°C group, and from August 30 in 15L9D/22-24°C group. How-ever, much more eggs were obtained in the 12L12D group than that in the 15L9D group. No mature fish were found in the 15L9D/28-29°C group. These results indicate that the decrease in temperature is the main environmental cue that initiates the autumn spawning, and that short daylength accelerates gonadal maturation.In order to investigate the factors which terminate the autumn spawning, mature fish were divided into 3 groups; reared under 1) temperature changed group (23°C→19°C→16°C→14°C→11°C; 13L11D), 2) natural temperature group (13L11D), 3) daylength changed group (13L→11L→9L→15L→11L; 22-24°C) in the autumn spawning season. In the temperature changed group, daily spawning continued until the temperature decreased to 14°C. In natural temperature group, daily spawning was observed above 13°C. In the daylength changed group. daily spawning was observed under 13L11D, 11L13D and 9L15D. Spawning, however, stopped under 15L9D, and resumed under 11L13D. The number of spawned eggs/fish increased with the decrease in daylength. These results indicate that the low temperature in early winter is the terminating cue of the autumn spawning season.