Exposure to 17β estradiol causes erosion of sexual dimorphism in Bluegill (Lepomis macrochirus).

Estrogenic compounds including 17β estradiol (or E2) are known to negatively affect the reproductive system of many animals, including fish, leading to feminization, altered sex ratio, reduced fecundity, and decreased gonadosomatic index. The objective of this study was to evaluate the effects of varying concentrations of water-soluble 17β estradiol exposure on the external morphology of Bluegill. An experiment was set up where fish were individually maintained in 10-g tanks and exposed to 17β estradiol concentrations of 40 and 80 ng/L or no 17β estradiol exposure (the control). Fish were exposed for 21 days, with 17β estradiol replenished each week to account for 17β estradiol half-life. Fish were photographed laterally before and after the 21-day exposure to 17β estradiol. Landmark-based geometric morphometrics were conducted in MorphoJ and canonical variate and discriminant function analysis were used to compare the morphological changes in the fish under 17β estradiol exposure. The results showed that 17β estradiol exposure caused male dimorphic characters to change in Bluegill by becoming less prevalent. Specifically, there was a narrowing of the caudal peduncle, smaller nape protrusion, reduced opercular flap and pectoral fin, and a deeper body in the exposed groups compared with control fish under both concentrations. This research highlights the widespread effects of 17β estradiol on fish health beyond the reproductive system, which could have important conservation implications by affecting mate selection and reducing reproductive success.