Melanophore comparisons in different forms of ambicoloration in the flatfish Pseudopleuronectes americanus and Reinhardtius hippoglossoides

The melanophores associated with contrasting manifestations of ambicoloration in two species, winter flounder (Pseudopleuronectes americanus) and Greenland halibut (Reinhardtius hippoglossoides), from the Pleuronectidae are compared microscopically. Winter flounder is a benthic inshore species, whilst Greenland halibut is a deep water species considered to spend the greater part of its life away from the sea floor, although the relatively thick blind‐side epidermis associated with a benthic life occurs in both species. Various forms of abnormal ambicoloration occur in some specimens of winter flounder. Melanophores from the flounder blind side are morphologically similar to those from the ocular side in the different forms of ambicoloration, although there are differences in melanophore densities. In Greenland halibut, ambicoloration is a normal characteristic which is considered to be secondarily acquired. The melanophores of the ocular side of Greenland halibut are similar to the melanophores of other Pleuronectidae, whereas those of the blind side are very different in morphology and size.