A very distinct semilunar spawning cycle was found in a population of the d
amselfish Dascyllus aruanus on the coral reefs of Sesoko Island, Okinawa. S
pawning occurred from June to September, only in the early morning, during
a period of 2-4 days immediately before or around the time of the new and f
ull moon. Males cared for the eggs deposited on the substrate for 2.5 days
until hatching. Hatching occurred just after sunset, i.e., at the high tide
of spring tide; the strong ebb current then would rapidly disperse the new
ly hatched larvae offshore. Females tended to synchronize spawning in a mal
e's nest, also because multiple clutches in a nest would be more likely to
survive until hatching. Thus, the distinct semilunar spawning cycle may fav
or females in reducing mortality of both eggs and larvae.