Sex change in a coral-reef fish: dependence of stimulation and inhibition on relative size.

The removal of a single dominant individual has been shown to trigger a sex change in some coral-reeffish. In the saddleback wrasse (Thalassoma duperrey), however, female-to-male sex change requires visual stimulation from smaller conspecifics. This change is not dependent on the sex or color of the stimulus fish and can be inhibited by larger conspecifics. On the reef, a female probably changes sex when the relative numbers of larger and smaller conspecifics change within her home range.