Identification of Gender in Yellow Perch by External Morphology: Validation in Four Geographic Strains and Effects of Estradiol

External morphological criteria that enable the rapid determination of gender have been developed for Yellow Perch Perca flavescens. Criteria are based upon (1) shape of the urogenital papilla (UGP), (2) size of the UGP relative to the anal (AN) opening, and (3) coloration of the UGP. In females, the UGP appeared (1) rounded at the anterior margin, (2) pointed at the posterior margin and had a V or U shape (crescent shaped in mature animals), (3) generally lacked reddish coloration, and (4) narrower relative to the AN. In males, the UGP (1) appeared circular or oval around the entire margin, (2) typically displayed reddish coloration, and (3) was generally wider relative to the AN. To verify accuracy of these criteria, gender was verified internally in perch of various sizes, sex, and maturity from four domesticated geographic strains (n = 1,389). For all perch tested, accuracy was 97.3% for both sexes, 98.8% for females, and 95.9% for males. To experimentally verify accuracy of these criteria, juvenile Yellow Perch (n = 913) were treated with dietary 17-estradiol (E2; 15mg/kg diet) or a control diet. Accuracy was 97.7% for control females and 95.1% for control males, which diminished to 63.9% for the E2-treated females and 57.6% for E2-treated males. We developed a gender identification algorithm that will enable sorting of sexes for many uses including (1) collection of broodstock by new aquaculture producers, (2) management of broodstocks for existing producers, (3) improved selection criteria for genetic selection programs, (4) studies on gender-specific differences in Yellow Perch physiology, and (5) the unharmed release of fish in field and aquaculture settings. Uncoupling of external UGP morphology from actual gender in E2-treated perch can enable producers and biologists to detect exposure to estrogenic compounds in areas where endocrine disruption is suspected. Received October 11, 2012; accepted March 5, 2013