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Colour pigments in the penpoint gunnel Apodichthys flavidus and their ecological significance Wilkie, Donald Walter

Abstract

Field and laboratory studies were undertaken to examine the ecological role of colouration in the penpoint gunnel Apodichthys flavidus, its structural basis and possible origin. A. flavidus was found to vary in colour from green through brown to red. The vast majority of fish collected matched at least one type of vegetation from their habitat. Those observed directly within vegetation were of the same colour as the vegetation. In habitat selection experiments A. flavidus was found to prefer cover under rocks to that within vegetation, but when provided with vegetation alone chose that which it matched. The colour phases observed in A. flavidus were found to be determined directly by the pigments they contained not by differences in stages of chromatophore expansion. Green fish owe their colour primarily to esterified dihydroxy ε carotene conjugated with a protein and dispersed throughout the integument. The colour of red fish results primarily from esters of astaxanthin contained in erythrophores. Brown fish incorporate the colouration systems of both the red and green phases, but the modifications involved have not been fully worked out. Colour change experiments showed that A. flavidus cannot undergo complete changes of colour phase in response to environment alone. Diet has an influence on colour, but complete colour changes were not produced experimentally. Larvae were reared from the eggs of green and brown individuals. All developed colouration more similar to that of the Artemia upon which they were fed than to their parental type. This evidence is discussed in terms of a possible dietary origin of colour variation and weighed against polymorphism. It is suggested that the colouration of A. flavidus has a cryptic function which is of importance primarily during food seeking. It is hypothesized that the vegetation upon which A. flavidus larvae settle in conjunction with early diet primarily determines the colouration of individuals.

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