Bluehead wrasse
(Thalassoma bifasciatum)

Thalassoma bifasciatum, the bluehead, bluehead wrasse or blue-headed wrasse, is a species of marine ray-finned fish, a wrasse from the family Labridae. It is native to the coral reefs of the tropical waters of the western Atlantic Ocean. Its main range includes the Caribbean Sea and the southeast area of the Gulf of Mexico.

Young/small females and males have yellow upper bodies and white lower bodies, often with green or black lateral stripes and occasionally dark vertical bars. This coloration is known as the initial phase. They can rapidly alter the presence or intensity of their yellow color, stripes, and bars, and these color changes appear to correspond to behavioral changes. Large females and some males can permanently change coloration and/or sex and enter the terminal phase coloration, which has a blue head, black and white bars behind the head, and a green body. This color phase gives the species its name. Terminal phase males are larger (70 to 80 mm) than the initial phase males (60 mm).