Serrasalmus is the classic piranha genus of South America, a group of deep-bodied, laterally compressed characins carrying a single row of tightly interlocking, razor-edged teeth built for slicing flesh. The atlas covers 34 species, sized from about 4.5 in to 16.5 in, drawn from across the continent's major river basins — records include Brazil, Venezuela, Peru, Argentina, Bolivia, Colombia, Guyana, and Paraguay, tracing the Amazon, Orinoco, and neighboring drainages where the genus is most diverse. Most species travel in loose shoals and are opportunistic predators and scavengers, feeding on fish, fins, invertebrates, and carrion; their reputation as indiscriminately dangerous is considerably overstated in popular culture, though the bite and dentition are genuinely formidable.
Serrasalmus rhombeus, the black piranha, is the best known species to aquarists and is one of the most widely kept large predatory characins in the specialist trade, prized for its aggressive character and impressive dentition; other species such as Serrasalmus sanchezi (the green tiger piranha) and Serrasalmus manueli (Manuel's piranha) are also sought after for their striking coloration. Keeping any Serrasalmus demands a large, secure tank and careful stocking, since most species are intolerant of tankmates and, in several cases, of each other outside a properly conditioned shoal. Conservation status across the genus is generally favorable — the atlas records a majority of Least Concern and unevaluated species, with only isolated Endangered and Critically Endangered listings — consistent with piranhas being widespread, adaptable predators across most of their South American range.