Female-female spawning and sex change in a haremic coral-reef fish, Labroides dimidiatus

In the polygynous coral-reef fish, Labroides dimidiatus, the largest female may complete sex change within a few weeks if the male disappears. We cond ucted male removal experiments just prior to spawning time. The largest fem ale possessing ovulated eggs spawned in the male role with smaller females, 1-2 hr after the male removal, suggesting that ovulation could not prevent male sexual behavior. During the female-female spawning eggs were actually released, but of course unfertilized. The largest female subsequently spaw ned in the female role when the male was im mediately returned. If the male was never returned, such spawning behavior was repeated almost every day u ntil the largest fish was able to release sperm. Smaller females will parti cipate in such fruitless spawning according to their preference for larger mates. The largest females should perform male sexual behavior to secure fu ture mates, even before completion of gonadal sex change.