Stoplight Parrotfish

The Stoplight Parrotfish (Sparisoma viride) is a sex-changing fish inhabiting coral reefs in Florida, Caribbean Sea, Gulf of Mexico, Bermuda and as far south as Brazil. Its typical length is between 1–1.5 ft (30–46 cm), but it can reach 2 ft (61 cm) at times. It is normally found during the day between 15–80 ft (4.6–24 m).

Initial phaseThe colors of the stoplight parrotfish in the initial phase, when it could be either a male or a female, are dramatically different from those in the terminal phase, when it is definitely a male.

The common name, stoplight, comes from the marked yellow spot near the pectoral fin, which is clearly visible only in specimens in the terminal phase.
(credit: http://en.wikipedia.org/wiki/Stoplight_parrotfish)