Acestrorhynchus is a genus of slender, torpedo-shaped predatory characins, often grouped with the piranhas and their relatives, native to South American river systems across Brazil, Peru, Colombia, Venezuela, Guyana, Bolivia, Ecuador, and Argentina. The atlas covers 14 species ranging from about 2.5 in up to 17.5 in, and nearly all share the same hunting body plan: an elongated, streamlined body, a large mouth armed with fang-like teeth, and a forked tail built for fast pursuit rather than sustained cruising. They are open-water ambush and pursuit predators, feeding mainly on smaller fish, and their common name, freshwater barracuda, borrowed by species such as Acestrorhynchus falcatus and A. falcirostris, reflects that same predatory silhouette rather than any close relationship to the marine barracudas.
The genus is more a curiosity for predatory-fish specialists than a mainstream aquarium group, since its members need long, open swimming space and a diet of live or appropriately sized prey fish rather than typical community-tank fare, and they can be nervous, fast-moving tankmates unsuited to smaller setups. Named species in the atlas include the red-tail barracuda (A. altus), striped barracuda tetra (A. isalineae), pike characin (A. microlepis), dwarf redtail barracuda (A. nasutus), and Pantanal pike characin (A. pantaneiro). Most of the genus is assessed as Least Concern, with only a couple of species listed as Data Deficient, suggesting a group that is widespread and reasonably well studied across its South American range.