Comparative study on origin and formation of lunar-synchronized spawning in reef fish

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In order to clarify origin and formation of lunar-synchronized spawning activities in reef fish, annual reproductive cycle and spawning rhythm of fish inhabiting tropical coral reefs in Central Java, Indonesia were examined. Most studies were carried out using rabbitfish, because similar studies have been conducted in sub-tropical coral reefs in Okinawa, Japan. When the fish were monthly collected from coral reef or purchased from fishermen, most fish had definite reproductive seasons, which occurred around changing season from dry to wet or from wet to dry. During the reproductive season, the fish were collected weekly according to lunar periodicity in order to know spawning rhythm. As a result, rabbitfish species repeated a lunar-related spawnings during the reproductive season. For example, the golden rabbitfish, Siganus guttatus, developed the gonads toward and spawned around the first quarter moon. Comparison of lunar-related spawning activity between Central Java, Indonesia and Okinawa, Japan, revealed that the golden rabbitfish spawned around the same lunar phase (the first quarter moon). The present study suggest that the fish have annual reproductive season which is closely related to regional environments and that the same cues from the moon are used as Zeitgeber for synchronized spawning in any regions.