Coloration patterns of reef fishes are an important trait for mediating intra and interspecific interactions, as well as for taxonomic identifications. Here we report a specimen of Stegastes arcifrons that presented a previously unobserved and anomalous color variation on a coral reef at Isla del Coco, Pacific Costa Rica. This color variation is known as xanthism and has been reported in some damselfishes, usually associated with genetic anomally.

Keywords: reef fish, Tropical Eastern Pacific, color pattern, xanthism.