Lunar-synchronized spawning is a rhythmic event observed in several marine animals, including corals and fish inhabiting temperate and tropical water. In the case of Epinephelinae, fish migrate from the habitual site before the species-specific moon phase and form aggregation at the spawning site. However, it remains unknown how they perceive cues from the moon for initiating gonadal development and subsequent spawning. We hypothesized that fish use moonlight to synchronize reproductive events.
Using the honeycomb grouper Epinephelus merra, a tropical Serranidae, spawns around the time of the full moon, we demonstrate the successful induction of spawning in this species by controlling light condition at night. Following three months of acclimatization under long days at 28°C, mature fish were reared under an artificial full moon or new moon conditions at night.
Released eggs during the experiment were collected and quantified. In the result of that many eggs laid by the fish in the full moon group, but not by the new moon group, at 3 weeks after moonlight treatment (Table 1). Moreover, fish in the full moon group had a high gonadosomatic index and abundant yolk-laden oocytes in the ovary (Fig. 1). Therefore, our study demonstrated that the moonlight triggers gonadal development and subsequent spawning in lunar-synchronized grouper with a full-moon preference.