The widemouth gambusia is a species of fish in the family Poeciliidae of the order Cyprinodontiformes. It is endemic to Mexico, specifically to the Baños del Azufre near Teapa, Tabasco. The Baños del Azufre are sulfidic springs that contain high concentrations of toxic hydrogen sulfide. This prevents most animals from living in them; the only other fish found in the toxic sections of Baños del Azufre is the sulphur molly.