Taxonomy & naming
Serrasalmus compressus was described in 1991 by Michel Jégu, Astrogildo Leão and Ricardo Santos, part of a wave of Serrasalmus species-level revisions in the Amazon basin during that period. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, and to the genus Serrasalmus, the most speciose genus of true piranhas, distinguished from the shoaling genus Pygocentrus by generally more solitary, territorial habits and, in many species, a more laterally compressed body.
GBIF and FishBase both confirm the species and its type locality in the Rio Madeira basin, a major southern tributary of the Amazon. As with much of the genus, the Catalog of Fishes remains the reference point for the currently valid combination; this account keeps the genus as Serrasalmus per that authority and does not attempt to reinterpret the taxonomy from older or informal sources.
Morphology
Serrasalmus compressus shows the classic piranha build: a deep, strongly laterally compressed (hence the specific epithet) body, an underslung lower jaw, and a single row of interlocking, triangular, razor-edged teeth adapted for slicing rather than crushing. FishBase records a maximum size of 7.5 in standard length, though aquarium and hobbyist sources report specimens reaching roughly 8–10 in in captivity — a modest size within Serrasalmus, well short of the largest species in the genus.
Detailed published descriptions of adult colouration and pattern for this species are sparse beyond the original taxonomic description and FishBase's summary data; the cache used for this article does not include a full colour account, so keepers should expect the general silvery, dark-flecked Serrasalmus look typical of Rio Madeira piranhas rather than a distinctive, well-documented colour form.
Habitat
The species is native to the Rio Madeira basin and its tributaries in the Brazilian Amazon, one of the largest and most biodiverse sub-basins of the Amazon system. FishBase gives a natural temperature range of roughly 73–81 °F for the species, consistent with the broader pattern of warm, lowland Amazonian river conditions.
Detailed data on pH, hardness and specific microhabitat (main channel, floodplain, blackwater vs. whitewater tributary) were not found in the available sources for this species specifically; keepers should default to the general soft, mildly acidic-to-neutral water typical of Rio Madeira piranhas rather than assume extreme blackwater conditions without direct evidence.
Feeding
Serrasalmus compressus is a carnivorous opportunist, consistent with the genus as a whole: aquarium sources describe it taking pellets, fresh and frozen meaty foods, consuming a portion within two to three minutes when fed in small, multiple meals. As with other true piranhas, fin-nipping and predation on smaller fish are part of its natural feeding behaviour, not an aquarium aberration.
In the aquarium, a varied diet of fish fillet, prawn, mussel and quality carnivore pellets is appropriate; live "feeder" fish should be avoided on general disease and nutrition grounds. Given its predatory nature, any tankmates need to be too large or too fast to be treated as prey.
Mating
Published courtship and pairing behaviour specific to Serrasalmus compressus is essentially undocumented. Aquarium sources note that this species is prone to territorial aggression and stress when kept alone, and that group or paired housing with adequate space is advised over solitary keeping — but this reflects general husbandry guidance rather than an observed courtship sequence.
No external sexual dimorphism has been documented for this species in the sources available; data is sparse enough that this account does not speculate further on sexing or pairing behaviour.
Breeding
As in other true piranhas (Serrasalmus and Pygocentrus), the expected mode for this species is substrate spawning: a pair clearing and defending a nest site among plants or debris, with adhesive eggs guarded and fanned, often primarily by the male, until hatching within a few days. However, aquarium and forum sources consulted for this species specifically report that spawning in captivity is rarely documented, and that breeding substrate choice and fecundity data are sparse in the aquarium literature for Serrasalmus compressus in particular.
Given that gap, this account does not claim confirmed captive breeding for the species — only that its expected reproductive mode, by analogy with its genus, is a guarded substrate nest rather than egg-scattering, mouthbrooding or bubble-nest building. Prospective breeders should treat this as an underdocumented area rather than a solved one.
In the aquarium
Care sources describe Serrasalmus compressus as naturally living in small groups in the wild but prone to aggression and stress when kept as a lone solitary individual without adequate space — hobbyist guidance suggests a large tank, cited at roughly 185 US gal and up, for a small group, with heavy cover and enough room to establish separate territories. A stressed or lonely individual is reported as more susceptible to disease, so adequate tank size and cover matter as much for this species as for its shoaling relatives.
As with other true piranhas, the jaws are genuinely capable of a serious bite, and fish should be moved by container rather than net. Tankmates should be limited to species too large or fast to be seen as prey, and fin-nipping toward slower tankmates is a realistic risk. Finally, piranhas of this genus are restricted, permit-controlled or banned outright in many U.S. states and countries, so keepers must check local and state law before acquiring one, and must never release a piranha into open water.
Conservation
Serrasalmus compressus has not been formally assessed by the IUCN Red List; its status is Not Evaluated. This is common among Serrasalmus species restricted to specific Amazon sub-basins that have not yet been the subject of a dedicated conservation assessment, rather than any indication that the species is known to be at risk.
As a Rio Madeira basin endemic, the species sits within a system that has faced substantial pressure in recent decades from large hydroelectric dam construction (notably the Santo Antônio and Jirau dams) and associated habitat change; that broader context is a reasonable long-term watch item for Rio Madeira fish generally, though no species-specific conservation data for Serrasalmus compressus was found in the sources consulted for this article.