Gnatholebias W. J. E. M. Costa, 1998 Pterolebias is a genus of killifish from the family Rivulidae which are native to temporary swamps and ponds in South America.

It includes two groups, which sometimes are regarded as separate genera: Pterolebias (sensu stricto) from the southern Amazon and Paraguay (including the Pantanal) river basins, and Gnatholebias from the Orinoco (including the Llanos) river basin.

[2] Depending on the exact species, these annual killifish reach up to 7–12 cm (2.8–4.7 in) in total length.

[3] There are four recognized species in Pterolebias according to FishBase,[3] but two of these are sometimes placed in a separate genus, Gnatholebias.

The two groups are relatively distantly related and if kept in a single genus Pterolebias is paraphyletic.