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Bizarre as it might sound, sex change is quite common in the fish world.
Some species of fishes such as sharks and rays are born one sex and stay that sex throughout life.
For species that change sex there may be up to three colour phases. The first is a juvenile phase colouration shown by immature fishes. As a juvenile fish grows it develops the initial phase (IP) colouration. This may resemble the juvenile phase colouration or be quite distinct. The IP colouration is usually drab, comprising mostly grey, brown and red.
IP individuals are usually female but IP males do exist in some species. These IP male fishes are known as primary phase males. They look identical to females.
A female that changes into a TP fish undergoes not only a change of colour but also a change of sex.
- Choat, J.H. & Bellwood, D.R. in Paxton, J.R. & W.N. Eschmeyer (Eds). 1994. Encyclopedia of Fishes. Sydney: New South Wales University Press; San Diego: Academic Press . Pp. 240.