Morphological skin colour changes in teleosts

Morphological skin colour change in fish is often referred to in the sole context of background adaptation. It is becoming increasingly apparent that it is a broad phenomenon elicited by a variety of factors. To date, no review has attempted to integrate the different types of morphological colour changes occurring in teleosts, their ecological origins and the regulatory mechanisms involved, often restricting the view on the subject. First, the origin of skin colour is addressed in teleosts including chromatophore type and distribution, pigment biosynthetic pathways and their interactions to one-another. Second, the different types of morphological colour changes occurring in teleosts are categorized and a key distinction is made between proximate and ultimate morphological colour changes. These are defined respectively as the change of phenotype during an established life-stage in response to environmental interactions and during the transition between two developmental-stages phenotypically pre-adapted to their ancestral ecosystems. Nutrition and UV-light are primary factors of proximate morphological colour changes beyond the control of the organism. By contrast, background light conditions and social interactions are secondary proximate factors acting through the control of the organism. Highly diversified among teleosts, ultimate morphological skin colour changes are presented in term of alterations in skin structure and pigment deposition during metamorphosis in different species. Finally, the physiological and endocrine mechanisms regulating both proximate and ultimate morphological colour changes are reviewed.