Numerous fish genera include species whose individuals can change their sex, a process called sequential hermaphroditism. Among coral reef fish, fo example, both protogyny ("first female", a change from female to male) and protandry ("first male", a change from male to female) occur. In fish that practice protogyny (f.i. Thalassoma bifasciatium), the sex change appears to be under social control. These fish commonly live in large groups, or schools, where successful reproduction is typically limited to one or a few large, dominant males. If those males are removed, the largest female rapidly changes sex and becomes a dominant male.