A study on the golden rabbitfish Siganus guttatus, which
spawns synchronously around the fi rst-quarter moon during
the reproductive season, showed daily fluctuations of melatonin
concentration in the blood, which were low during the day and high at night
In addition, plasma melatonin concentration at the new moon was higher than
at full moon. When the fish were exposed to moonlight at midnight of both of these moon phases, the melatonin concentration decreased to the control
levels.These results show that the fish possibly perceive moonlight intensity and that plasma melatonin fluctuates according to brightness at a certain
time of night. Fish kept in constant darkness or light at night did not spawn.
It is possible that night conditions are related to synchronous gonadal development and spawning in the golden rabbitfish