Sexual Dimorphism in Pelvic Fin Length of Two Endangered Freshwater Atherinopsid Species with High Aquaculture Potential

The endemic Mexican silversides of Lake Pátzcuaro (Pike Silverside Chirostoma estor) and Lake Chapala (Blacknose Silverside C. promelas) are endangered fish species of great socioeconomic importance in the region. Since the last decade, much progress has been made to close the life cycle in captivity and in promoting the aquaculture of these species. The lack of standardized husbandry and broodstock management practices, including sex discrimination, is a bottleneck to the commercial culture of these species. Recent observations have suggested a possible difference between the length of the pelvic fins of males and females. To explore these observations, biometric measurements were taken from Pike Silverside and Blacknose Silverside broodstocks, comprising body weight, SL, distance from the base of the pelvic fin to the genital pore (BPF), and distance from the tip of pelvic fin to the genital pore (TPF). The latter measurements were used to calculate the TPF/BPF ratio. Sex‐specific differences were found in BPF, TPF, and TPF/BPF for both species, clearly indicating a sexually dimorphic characteristic not previously reported in any atherinopsid. This study reveals for the first time the presence of a noticeable sexually dimorphic and externally evident trait in two closely related atherinopsid species, which provides a simple morphometric technique for sex discrimination that minimizes manipulation and thus avoids overstressing or killing the fish