Piaractus is a genus of large, deep-bodied pacus in the piranha family Serrasalmidae, distributed across major South American river basins in Bolivia, Brazil, Colombia, Venezuela, Argentina, Ecuador, Paraguay and Peru. The atlas covers 3 species, and they are genuinely big fish, ranging from 19.5 in up to 34.5 in as recorded here. Unlike their piranha relatives, Piaractus species are primarily fruit-, seed- and plant-eaters, using rows of blunt, molar-like teeth to crack open nuts and seeds that fall into the water from riverside forest, a role that makes them important seed dispersers within their ecosystems.
Two species carry substantial economic and cultural weight in South America: Piaractus brachypomus (pirapitinga) and Piaractus mesopotamicus (pacu) are both widely farmed food fish and are also sold young in the aquarium trade under names like 'red pacu', though they grow far too large and too fast for almost any home aquarium and are routinely rehomed or released once owners realise their adult size. The third species, Piaractus orinoquensis (Venezuelan pacu), rounds out the genus. The IUCN picture is mixed, with one species Near Threatened, one Vulnerable and one not yet evaluated, reflecting pressure from overfishing and habitat change across their river ranges; none currently carry a CARES designation.