Effects of Photoperiod on Spawning Rhythm in the Tobinumeri-Dragonet Repomucenus beniteguri

Abstract

In order to record the daily spawning time of individual fish, one female and two male tobinu-meri-dragonet were reared in separate indoor tanks (1×2×0.8 m) from September 30. The photo-period in each tank was regulated by a timer and water temperature was maintained at 22-24°C during the experiment and the spawning time was determined by checking the existence of spawned eggs on the net placed at the overflow outlet of each tank every 15 minutes.
In experiment 1, two females continued daily spawning. Spawning occurred during 1700-1900 hr when the fish were kept under a photophase of 0500-1900h (14L10D). When the photo-phase was shifted from 0500-1900h to 0100-1500h (14L10D), the spawning time was advanced by an average of 3.2 hours. Thereafter, we delayed the time of lights-on by 4 hours (10L14D); how-ever, spawning time was delayed only 0.7 hours. By delaying the time of lights-off by 4 hours (14L10D), spawning time was delayed 2.6 hours. In experiment 2, four females continued daily spawning. When the time of lights-off was advanced 4 hours (10L14D), spawning time advanced 3.1 hours. These results indicate that the spawning time is determined photoperiodically. The time of lights-off seems more significant than that of lights-on in the regulation of spawning time, indicating that “lights-off” is working as a synchronizer.