Nematocharax

{{Short description|Genus of fishes}}

{{Automatic taxobox

| image = Nematocharax costai (UFRJ 8216-l).png

| image_caption = Nematocharax venustus

| taxon = Nematocharax

| authority = S. H. Weitzman, Menezes & Britski, 1986

}}

Nematocharax is a genus of freshwater fish in the family Characidae. The species are endemic to Brazil. The generic name alludes to {{lang|grc|νήματος}} (nḗmatos), "threaded", referring to the long, thread-like fins; and Charax, a common name for genera in the order Characiformes, from {{lang|grc|χάραξ}} (chárax), meaning a pointed stake in a palisade, referring to their dentition.{{cite web | url = https://etyfish.org/acestrorhamphidae/ | title = Family ACESTRORHAMPHIDAE Eigenmann 1907 (American Tetras) | access-date = 15 April 2025 | author1 = Christopher Scharpf | author2 = Kenneth J. Lazara | name-list-style = amp | work = The ETYFish Project Fish Name Etymology Database | publisher = Christopher Scharpf and Kenneth J. Lazara | date = 23 March 2025}}