Nematocharax is a genus of freshwater ray-finned fishes belonging to the family Acestrorhamphidae, the American characins. The species are endemic to Brazil. The generic name alludes to νήματος (nḗmatos), "threaded", referring to the long, thread-like fins; and Charax, a common name for genera in the order Characiformes, from χάραξ (chárax), meaning a pointed stake in a palisade, referring to their dentition.

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