Poeciliopsis prolifica, or the blackstripe livebearer, is a species of small freshwater fish in the family Poeciliidae.

[5] The species is endemic to Mexico where it is only found on the eastern side of the Gulf of California, between the states of Sonora and Nayarit.

It is a shallow-water, freshwater fish, tolerant of brackish water and found at depths of less than 2 m (7 ft).

Its habitat includes streams, brackish lagoons, estuaries and mangrove areas, with sand, mud or gravel bottoms.

[6] This fish is found in a limited part of Mexico and is very specific in its depth requirements, so it probably occupies a total area of less than 2,000 km2 (772 sq mi).