Grijalva River
The sulphur molly ("Poecilia sulphuraria"), locally known as "molly del Teapa", is a critically endangered species of fish in the family Poeciliidae. It is endemic to Mexico, specifically to the Baños del Azufre (Grijalva River basin) near Teapa, Tabasco. The Baños del Azufre are sulfidic springs that contain high concentrations of toxic hydrogen sulfide (). "Poecilia sulphuraria" has apparently evolved the ability to tolerate the toxic conditions. A few other "Poecilia" species are known from similar habitats in Mexico.