Taxonomy & naming
Pygocentrus piraya was described by Georges Cuvier in 1819, one of the earliest formally named piranhas, and it has carried several historical combinations in the literature, including Serrasalmus piraya and Serrasalmo piranha, before settling in the genus Pygocentrus alongside P. nattereri, P. cariba and P. ternetzi. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises Pygocentrus piraya (Cuvier, 1819) as the valid combination; it belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes.
The piraya is set apart from its congeners chiefly by its restricted distribution and its size: it is endemic to the rio São Francisco basin of eastern Brazil, a system isolated from the Amazon and Paraná-Paraguay drainages, and it grows larger than any other recognised Pygocentrus species. The common name "piraya" is itself a regional Brazilian-Portuguese rendering of the same Tupi root behind "piranha" — pira (fish) plus a form referring to teeth or cutting.
Morphology
The piraya shares the classic Pygocentrus silhouette: a deep, laterally compressed, almost diamond-shaped body, a blunt head with a strongly underslung lower jaw, and a single row of interlocking, tricuspid, razor-edged teeth in both jaws that shear rather than tear. As in other piranhas, teeth are replaced in sets rather than singly, so the bite stays functional through the fish's life.
FishBase records a maximum length of 13.5–15 in standard length and a weight up to 3.2 kg, making the piraya the largest confirmed member of its genus — noticeably bigger than the red-bellied piranha's more typical wild size. Colouration follows the general Pygocentrus pattern of a silvery body with a deepening, ruddy wash on the throat, belly and lower fins in mature fish, though the piraya's colouring and body proportions are documented mainly through aquarium-trade and fishery accounts rather than a dedicated colour study; data on precise ontogenetic colour change is comparatively sparse.
Habitat
Pygocentrus piraya is endemic to the rio São Francisco basin in eastern Brazil, including tributaries such as the rio das Velhas and the rio Grande, and it has also been documented in the rio de Contas system of Bahia, a separate coastal drainage near the São Francisco's mouth. This is a comparatively narrow range for the genus — most other Pygocentrus species range across the much larger Amazon, Orinoco or Paraguay-Paraná systems — and it reflects the São Francisco's long geological isolation from neighbouring basins.
SeriouslyFish reports a temperature range of 68–82 °F, pH 6.0–8.0 and general hardness of roughly 36–357 ppm, a broader and more neutral-to-alkaline tolerance than the softer, more acidic water typically associated with Amazonian Pygocentrus populations. The São Francisco is a warm-temperate-to-tropical river with strong seasonal flow variation, and as with other piranhas the species is expected to use flooded marginal vegetation and submerged structure for cover, though detailed habitat-use studies specific to the piraya are limited.
Feeding
SeriouslyFish and diet studies from the rio de Contas describe Pygocentrus piraya as an opportunistic carnivore/omnivore, consistent with the rest of its genus: live fish, aquatic invertebrates and insects, along with nuts, seeds and fruit taken from overhanging or fallen vegetation. A comparative wild-diet study along the rio de Contas in Bahia examined P. piraya alongside the sympatric Serrasalmus brandtii and found both species carnivorous and opportunistic in their feeding, rather than specialised hunters.
As in other true piranhas, fin- and scale-nipping — taking a bite from a passing fish rather than killing it outright — is a documented part of the feeding repertoire and a major reason the genus has an outsized reputation relative to its everyday behaviour. In captivity, the piraya takes bloodworm, earthworm, prawn and fish strips readily; keepers are cautioned against relying on live "feeder" fish, which carry disease and quality risks, and against feeding it fatty, poorly balanced meat as a diet staple.
Mating
Specific courtship behaviour for Pygocentrus piraya has not been documented in the cache's sources, and no dedicated study of its mating display appears to exist in the literature reviewed here. Given its close relationship to P. nattereri, a shoal-based pairing pattern — a ripe pair separating from the group and becoming territorial around a chosen substrate site as water conditions shift — is plausible, but this should be treated as an inference from its congener rather than a documented fact specific to the piraya.
External sexual dimorphism has not been reported for this species; as in other Pygocentrus, gravid females may appear fuller-bodied when in spawning condition, but no reliable colour or fin-based method for sexing the piraya is documented.
Breeding
Breeding in Pygocentrus piraya is unrecorded in captivity according to SeriouslyFish, which notes that the wild spawning pattern likely follows the same substrate-nesting mode documented in P. nattereri — a pair clearing and defending a nest site amid flooded marginal vegetation during seasonal water-level changes, with adhesive eggs laid on the substrate and guarded at the nest. As in other true piranhas, this would make it a substrate egg-layer rather than a mouthbrooder or bubble-nest builder, but for the piraya specifically this is an inference from its genus, not a directly observed spawning event.
Given the lack of aquarium breeding reports, prospective keepers should not expect to reproduce this species at home; the trade in P. piraya is understood to rely substantially on wild-collected or regionally sourced fish rather than captive-bred stock, unlike P. nattereri, which is bred commercially.
In the aquarium
The piraya's size is the first consideration for any keeper: at up to 13.5–15 in and over 3 kg, it is the largest Pygocentrus species and needs a genuinely large aquarium, well beyond what suffices for the more commonly kept red-bellied piranha. As a shoaling fish, it should be kept in a real group rather than alone — a solitary piraya in a bare tank is a stressed, defensive animal, not a tamer one — with dense cover from driftwood, roots or robust plants and dim, low-disturbance lighting to help a nervous shoal settle.
Aquarium-trade sources note that the species produces substantial waste at its adult size and needs strong filtration and a committed water-change routine; reported lifespan in good conditions is around 10 years. Mature individuals can become cannibalistic toward tankmates, including conspecifics, so stocking density and space matter as fish grow. As with all Pygocentrus, the jaws are genuinely powerful and the fish should be moved by container rather than net; keepers must also check local and state law, since piranhas of this genus are restricted, permit-controlled or banned outright in many U.S. states and countries, and a piraya must never be released into open water.
Conservation
Pygocentrus piraya is assessed by the IUCN Red List as Least Concern, with a stable population and no major identified threats, reflecting the fact that it remains widespread and abundant within its native rio São Francisco basin. Its single-basin endemism, however, makes it inherently more exposed than wide-ranging congeners such as P. nattereri to basin-scale pressures — damming, water abstraction and habitat alteration along the São Francisco, one of Brazil's most heavily engineered river systems — even though the species is not currently classified as threatened.
Some countries and jurisdictions impose regional restrictions on Pygocentrus piraya out of concern over its potential as an invasive predator if released outside its native range, a precaution applied across the genus rather than one specific to any documented established population of this species. Because captive breeding has not been reported, aquarium demand for the piraya likely draws on wild or regionally collected stock from the São Francisco system.