Anostomids have elongated bodies ranging from 15 to 60 cm (5.9 to 23.6 in) in length; their shape varies between fusiform and deeper-bodied, but even the latter are only moderately laterally. They have elongated, tapering heads with rather long, straight snouts, and small apical to upturned mouths immediately at or near the snout tip. This family contains many headstanders, which habitually swim with their heads pointing from 45° up to 90° downwards; most feed on plants near the bottom, while others also eat detritus and invertebrates picked up from river- or lakebeds. Adults guard the eggs after spawning. Anostomidae are generally considered edible, and some of the larger species are caught for food on a regular basis, much like large Leuciscinae (which are superficially similar Cypriniformes) are in the temperate Northern Hemisphere.

Their jaws are rather short, with the maxillary bone small and excluded from the mouth opening, while the ascending process of the premaxilla is triangular in overall shape and robustly developed. One row of six or eight curved teeth occur in each jaw, arranged by length in a step-like fashion, with the front teeth being the longest; the pharyngeal teeth are enlarged and have two or more cusps each.