Sexual Dimorphism in Plains Minnow,Hybognathus placitus

Abstract

Abstract Hybognathus placitus collected from several west Texas streams exhibit sexual dimorphism in body form, which is unusual in cyprinids. Seventeen morphological measurements, including standard length, were made on 62 specimens and analyzed for sexual dimorphism. Partial warp scores were used to describe sexual dimorphism in body shape. There was no difference in standard length between males and females (ANOVA, P = 0.9038, F1,60 = 0.0147), but there was a highly significant (MANOVA, F1,60 = 4.78, P < 0.001) sexual dimorphism in body shape. Overall, males have relatively longer first dorsal fin rays, larger heads, and caudal peduncles, whereas females are deeper bodied and have relatively longer trunks, from the pelvic fin insertion to the anal vent. Differences between male and female H. placitus in length of the first dorsal fin ray are readily apparent and can potentially be used for field identification.