Research on populations of the family Mugilidae is necessary for the framework of their good use and conservation, given the documented spatial-temporal variation in their attributes and biological processes. Mugil curema has also shown particularities in the southeastern Gulf of California, which should be considered. In total, 626 individuals were collected from February 2015 to August 2016. The gonad development pattern was asynchronous and divided into six ovarian and five testicular phases. The sex succession as size increases, the presence of only males in smaller sizes, some aspects of the ovarian structure, and the eosinophilic cells in the ovarian stroma suggest that M. curema could be a protandrous hermaphroditic species. Thus, the size at sexual maturity was smaller in males (18.26 cm in total length) than in females (22.08 cm). This information is greatly relevant for fishery management measures and the sustainable use approach and, at the same time, arouses interest in future research.