Incongruence between the sexes in preferences for body and dorsal fin size in Xiphophorus variatus

► We examined whether the sexes share a bias for sailfin-like dorsal fins in Xiphophorus variatus, a trait not present in their evolutionary history. ► Previous studies of X. variatus and other poeciliids observed female biases for males of larger dorsal fin size and lateral projection area (LPA). ► In this study, we tested male X. variatus preferences for dummy females varying in dorsal fin size, body size, and dorsal fin:body size ratio. ► Males preferred larger-bodied females when fin size and total LPA were held constant, but not for larger fins when body size was held constant. ► Unlike the permissive preferences of females, males discriminated between female body size (an indicator of fecundity) and fin size.