The winter flounder, Pseudopleuronectes americanus (Walbaum), population off Newfoundland can include a ‘non-reproductive post-mature’ subset at any time together with ‘reproductive’ and ‘immature’ subsets. Skin samples were taken from male and female specimens from each subset in the winter, after reproductive flounder have normally undergone a pre-winter phase of gonadal recrudescence, and also during the spring prespawning period and in the summer following spawning. Results for immature flounder demonstrate that fish size influences epidermal thickness in this species. The epidermis of reproductive flounders is thick, representing a secondary sexual characteristic, during gonadal recrudescence. A thick epidermis is most pronounced on the blind-side, particularly in prespawning males. Although the epidermis of non-reproductive post-mature fish was thinner than in prespawning males and females, it was thicker than in immature flounders. Also, the epidermal thickness of non-reproductive post-mature individuals can still display some seasonal change although gonadal recrudescence has not been sustained. There is also a relationship between condition factor and epidermal thickness which is manifested particularly clearly in immature and non-reproductive post-mature flounder.