The Anostomidae are a family of ray-finned fishes that belong to the order Characiformes. Closely related to the Chilodontidae and formerly included with them, the Anostomidae contain about 150 described species. Commonly known as anostomids, they are found in freshwater habitats from the Río Atrato in northernmost South America to warm-temperate central Argentina; they are of Amazonian origin, with few found west of the Andes (mainly in Colombia and Venezuela). Their scientific name approximately means "mouth on top", from Ancient Greek áno- (ἄνω) "up" (as an adverb) + stóma (στόμᾶ) "mouth", in reference to the arrangement of these fishes' mouth opening.