| Heterandria formosa, Poeciliidae, Girardinus, Limia, Cyprinodontiformes|
Heterandria is a genus of livebearing fishes within the family Poeciliidae. Most species occur in Guatemala and its surroundings, particularly Mexico, but the midget livebearer (H. formosa) comes from the southeastern United States.
Though many Poecilidae are familiar aquarium fishes, e.g. guppies, mollies, platys and swordtails, species within Heterandria are not commonly kept as fish. Somewhat more frequently found in aquaria is H. formosa, perhaps because it is one of the smallest known fish species in the world; its diminutive males are probably the smallest fish easy to keep as a pet. Species in this genus resemble egg-laying Cyprinodontoidei such as Fundulidae (topminnows) at first glance, and are thus sometimes called "killifish" though this is technically erroneous.
FishBase currently recognize 10 species in this genus, but based on genetics, external characters, morphometrics and meristics H. formosa (the type species of the genus) is not closely related to the remaining, which should be moved to their own genus, Pseudoxiphophorus. There are probably more remaining undiscovered as these fishes are rather inconspicuous. However, it is not very likely that many species remain unknown to science as this is genus is only found in a rather restricted region, and only one new species has been discovered since 1980.Heterandria anzuetoi D. E. Rosen & R. M. Bailey, 1979
Heterandria attenuata D. E. Rosen & R. M. Bailey, 1979
Heterandria bimaculata (Heckel, 1848) (Twospot livebearer)
Heterandria cataractae D. E. Rosen, 1979
Heterandria dirempta D. E. Rosen, 1979
Heterandria formosa Girard, 1859 (Dwarf livebearer, least killifish)
Heterandria jonesii (Günther, 1874) (Barred livebearer, barred killifish)
Heterandria litoperas D. E. Rosen & R. M. Bailey, 1979
Heterandria obliqua D. E. Rosen, 1979
Heterandria tuxtlaensis McEachran & T. J. DeWitt, 2008