RESUMO
The California butterfly ray Gymnura marmorata is frequently caught by artisanal fisheries in north-western Mexico (Baja California Sur; BCS). The aim of this study was to estimate reproductive characteristics and describe the micro and macroscopic reproductive structures of female and male G. marmorata. Sampling was carried out at two fisheries landing sites located on the west coast BCS, from 2008 to 2012. The largest disc width (WD ) ever recorded for this species was 131.0 cm and females were larger than males. The male sample was composed exclusively of adult specimens, with a median size at 50% maturity (WD50 ) estimated at 44.9 cm WD . For females, size at onset of maturity was estimated at 63.0 cm WD ; WD50 , at 64.7 cm WD ; and size at pregnancy at 80.1 cm WD . Gonadal asymmetry was observed for the first time in this species. Indeed, in males only the left testis was functional (testicular asymmetry), while in females, only the left ovary was functional (ovarian asymmetry).