Pterolebias is a genus of annual killifish in the family Rivulidae, native to seasonal floodplain habitats across Brazil, Argentina, Bolivia, and Paraguay. The genus's 2 species in the atlas reach 3–4.5 in, notably large for annual killifish, with males typically showing elongated, flowing dorsal and anal fins - the trait behind the common name of the long-finned killifish (Pterolebias longipinnis). As annual fish, they inhabit temporary pools that dry seasonally, with eggs surviving the dry period buried in the substrate and hatching when the rains return.
Both species have a following among specialist killifish keepers who maintain the annual life cycle in captivity, incubating eggs through a dry diapause period before hatching them in fresh water - a demanding but well-established practice within the killifish hobby. Both Pterolebias longipinnis and P. phasianus carry a Least Concern IUCN status, consistent with a genus adapted to a naturally boom-and-bust seasonal habitat rather than one under specific documented human pressure.