The Monterrey platyfish (Xiphophorus couchianus) is a species of freshwater fish in family Poecilidae of order Cyprinodontiformes. A live-bearer, it is native to the vicinity of Monterrey, Mexico. IUCN lists the Monterrey platyfish, formerly widespread in Mexico, as Critically Endangered, upgraded from Endangered in 1996. The fish's population, numbering fewer than 250 individuals, is falling rapidly and is confined to a very small area, occurring only in fragmented pockets of habitat populated by few individuals. It is additionally suffering from environmental degradation.