A new species of the live-bearing fish genus Poeciliopsis from northern Mexico (Cyprinodontiformes, Poeciliidae)

: Poeciliopsis jackschultzisp. nov., is described based on seven specimens (17.9-26.7 mm SL) from the Rio Concepcion (also known as Rio Magdalena), Sonora, Mexico. The new species belongs to the Leptorhaphis species group and can be distinguished from other members of this group by features of the skeleton and colouration. The new species is sympatric with P. occidentalis, a hybridogenetic all-female biotype P. monacha-occidentalis, and hybrids between P. monacha-occidentalis females and P. jackschultzi males. The distribution of P. jackschultzi is highly restricted, and the main habitat, spring-fed marshy streams and pools, is susceptible to loss and degradation in a desert environment with increasing human water demand.