Color change and pigmentation in a color polymorphic cichlid fish

In many haplochromine cichlids, body coloration is an important communication cue during social interactions. In some cichlids, individuals can change color, but we have little information about the underlying physiological mechanisms. We examined the regulation of coloration in the color polymorphic cichlid fish Astatotilapia burtoni where males are either blue or yellow. Previous studies implicated the melanocortin system, a neuroendocrine center that regulates pigmentation and the stress response, in regulating the color polymorphism in this species. We found that both blue and yellow males express a high density of yellow xanthophores. Dispersal of xanthophore pigments in both yellow and blue morphs occurred within minutes in a dose-dependent manner. Similarly, exogenous α-melanocyte stimulating hormone (α-MSH, a melanocortin hormone) increased yellowness of the body in a dose-independent fashion. We observed many color changes in males housed in social communities with the proportion of yellow males increasing over the 2-week experimental period. However, color phenotype or color change was not influenced by experimental alteration of the stability of the social hierarchy. The effects of α-MSH suggest that the melanocortin system contributes to the polymorphism in coloration in A. burtoni but the role of social interactions and social stress in regulating color remains unclear.