Cypholebias is a genus of annual killifish in the family Rivulidae, native to seasonal wetlands of the Rio Uruguay drainage in Argentina and Uruguay. Like other annual killifish, Cypholebias lives in temporary pools that form during the rainy season and dry out completely for part of the year; adults complete their entire life cycle within a single wet season, and the population survives the dry months as drought-resistant eggs buried in the mud, which hatch once the rains refill the pool. The two species the atlas covers, Cypholebias cinereus and Cypholebias robustus, both reach roughly 2.5–3 in, a sizeable build for an annual killifish.
Annual killifish of this kind have a dedicated following among specialist killifish keepers, who reproduce the wild life cycle in miniature: fish are spawned into a peat substrate, the peat is dried and stored through a diapause period, and it is then rewetted to hatch the next generation, a technique that lets hobbyists exchange dried eggs internationally by mail. The genus is not a mainstream aquarium fish outside that community. Both Cypholebias species carry an elevated IUCN threat status in the atlas's records, consistent with the broader conservation picture for South American annual killifish, whose temporary-pool habitats are easily lost to wetland drainage and conversion to agriculture.