Not only can juvenile reef fish differ from the adults, in some species the sexually active males can differ from adult females and other sexually inactive adult males. The different body shapes and/or colorations are known as "stages".
In these species the first stage in the adult fish's life is the Initial Stage. The individuals in this stage are either adult females or adult males that are not sexually active. A male that becomes sexually active male is transformed into the Terminal Stage. Of course there are the intermediate transitional forms that may be seen as an individual transforms from one stage to another.
In the Stoplight Parrotfish, Sparisoma viridae, the Terminal Stage, the sexually active adult male, is the large green fish seen above. The Initial Phase, seen to the left, is the coloration born by either a female or by an adult male that is not sexually active.