Induction of spawning under artificial moonlight in the honeycomb grouper Epinephelus merra, a lunar-synchronized spawner

In the reproductive season, lunar-synchronized fish spawn during species-specific moon phases. 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 report the successful induction of spawning in this species by controlling light condition at night. Following 3 months of acclimatization under long days (14:10) at 28 ± 1.0°C, mature fish were reared under an artificial full (experimental group) or new (controls) moon during scotophase. Rearing fish under these conditions for 1 month resulted in successful spawning in the experimental group between 21h00 and 01h30. Similar results were obtained when control fish were subdivided into artificial full and new moon groups and reared for an additional month. Fish in the experimental group had a high gonadosomatic index and abundant yolk-laden oocytes in the ovary. Therefore, moonlight triggers gonadal development and subsequent spawning in lunar-synchronized fish with a full-moon preference.