Nematocharax is a small genus of characins (tetras) native to coastal river drainages in Brazil. As in the related genus Nematobrycon, the genus name points to threadlike, elongated fin rays that develop in males, a feature tied to the sexual dimorphism seen across this style of tetra. The atlas covers 2 species, Nematocharax costai and N. venustus, both small fish in the 2 in range, typical of the compact characins found in Atlantic-forest and coastal Brazilian streams.
Data on Nematocharax in the aquarium hobby are sparse; these are not widely traded fish, and most available information concerns their taxonomy and native range rather than tank care, so any husbandry approach should follow general best practice for small Brazilian stream characins - soft, warm, well-oxygenated water with cover. Conservation status is mixed within the genus: one species is assessed as Least Concern, and the other has not yet been formally evaluated.