Bluehead Wrasse juveniles

Description:

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" or IP for short. These individuals 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. It is this color phase that gives the species its name. The Terminal Phase males are larger (70 to 80 mm) than the Initial Phase males (60 mm).

Habitat:

Hunting Cay, Belize

Notes:

Initial phase females and initial phase males both can change into terminal phase males. However, this change in sex is permanent: once an initial phase female or male changes into a terminal phase male, it cannot change back. An experiment removing terminal phase males from a population showed that more females changed into terminal phase males, and even aggression levels increased and coloration changes occurred to signify the female's change to terminal phase male.