Fishes of this family are characterized by very elongate (pike-like) bodies covered with relatively small scales.
All teeth are conical and strong canines are present on the premaxilla, anterior part of the maxilla and the dentary. Small conical teeth are present on the ectopterygoid and minute conical teeth have been detected on the mesopterygoid of some species.
Other exclusive features of the group are: first infraorbital covering almost completely the maxilla when the mouth is closed; a branch of the laterosensory canal on the premaxilla; and rhinosphenoid bone in close contact with parasphenoid. The anal fin is falcate, never bearing hooks in sexually mature males and the origin of the dorsal fin is much nearer to caudal base than the tip of the snout. See Menezes (1969), Menezes (1992), Menezes & Géry (1983), Toledo-Piza & Menezes (1996) and Lucena & Menezes (1998).
The single genus Acestrorhynchus is currently represented by 15 species ranging from about 63 Acestrorhynchus minimus to 400 mm Acestrorhynchus falcirostris in standard length.
Acestrorhynchid species are entirely confined to South America and the greatest species diversity occurs in the Amazon and Orinoco basins. Three species occur further south in the São Francisco, Paraná, Paraguay and La Plata drainages. They are found in a variety of habitats, but primarily live in lakes, lagoons, areas near shore, and the smallest species are especially found in small streams (igarapés) of the Amazon basin (personal observation and see also Britski et al., 1986).
The peculiar dentition makes acestrorhynchid species very specialized predators among characiforms, most species feeding primarily on fishes. See Menezes, 1969a, Nico & Taphorn, 1985 and Amaral, 1990. After the major revision of Acestrorhynchus and the description of some new species (Menezes & Gery, 1983; Toledo-Piza & Menezes, 1996) not many new species are expected to be found.
Acestrorhynchids are not commercially important as food fishes and two of the smallest species (A. nasutus and A. minimus) might be eventually found in aquarium shops.