The Monterrey platyfish (Xiphophorus couchianus) is a species of freshwater fish in family Poecilidae.

A live-bearer, it was native to a very small section of the San Juan River system (itself part of the Rio Grande basin) in the vicinity of the city of Monterrey, Mexico.

[2][3] The specific name refers to the American soldier and naturalist Darius N. Couch (1822–1897) who collected the type on a self financed expedition to Mexico.

It has large black blotching, unlike the typical, unspotted form from the Huasteca Canyon.

[5] The Monterrey platyfish shares the title as northernmost naturally distributed Xiphophorus with the closely related northern platyfish (X. gordoni) and marbled swordtail (X. meyeri), which are two species that also are restricted to northeastern Mexico and seriously threatened.