Alternate Title

First Record of Reversed Symmetry in Etropus cyclosquamus and Second Record in Citharichthys spilopterus (Bothidae, Pisces) in the Gulf of Mexico, with a Plausible Genetic Explanation for Reversal


The discovery of the first instance of reversed eye symmetry in the shelf flounder, Etropus cyclosquamus, and the second instance in the bay whiff, Citharichthys spilopterus, are reported. Two reversed bay whiffs and three reversed shelf flounders were collected in the Gulf of Mexico. Four of these specimens were taken from the vicinity of Fort Walton Beach, Okaloosa County, in northern Florida, and one was taken from Higgs Beach in Key West, Monroe County, Fl. The collection of these fish is reported because of the infrequent occurrence of reversed eye symmetry in flatfishes in the Gulf of Mexico. The fish serve as the first record of eye symmetry reversal in E. cyclosquamus and the second record for C. spilopterus in the Gulf of Mexico. This is the second record of reversal for the genus Etropus and the third record for Citharichthys in the western Atlantic Ocean. The putative causes of symmetry reversal in pleuronectiform fish are briefly examined. A plausible genetic explanation for reversal is proposed. The explanation attempts to reconcile the environmental causality of eye symmetry with the accepted genetic model of Brown and Wolpert.