Reversal of sides in the blackfin flounder Glyptocephalus stelleri and variability of body pigmentation and shape in pleuronectid flatfishes

A specimen of the blackfin flounder Glyptocephalus stelleri showing a reversal of the body sides was found for the first time. Records of flounders of the genus Pseudopleuronectes with abnormal body coloration are given. The occurrence of pigmentation on both sides of the body and the reversal of sides are indicative of the manifestation of atavism in flatfishes. The high variability of phenotypic characters, which is common to some species of flatfish with clinal variations, is illustrated using the example of the marbled flounder.