This picture was taken from Here
Coral reefs are beautiful and exotic places full of all kinds of colorful and unique fish. Many of these fish may surprise you with something so foreign to us land walkers; they can change sex. These colorful fish like to maintain a certain ratio of male to female fish and if you remove one of their males a female will swiftly take his place. The opposite is true too of a male changing his sex and turning into a female and there are even fish that can be both sexes at the same time! I am not sure how these fish alter their sex since they must do it voluntary since there isn't something like temperature to force the fish to change its sex.