Taxonomy & naming
Serrasalmus maculatus was described by the Austrian ichthyologist Rudolf Kner in 1858, the same year and describer as the red-bellied piranha Pygocentrus nattereri, during the wave of nineteenth-century descriptions built from Central European museum collections of Brazilian material. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, and to the large genus Serrasalmus, whose roughly thirty valid species are notoriously difficult to tell apart and have a long history of taxonomic revision; a 2020 mitochondrial genetic study found evidence of a cryptic species complex within material identified as S. maculatus across the Amazon, Paraguay-Paraná and other river systems, meaning some populations currently carrying this name may eventually be split out.
The species epithet maculatus is Latin for "spotted" or "marked," referring to the dark blotching on the flanks. In the aquarium trade it is sold under the common name "maculatus piranha" and is sometimes confused with other small-to-medium spotted Serrasalmus species; as with the genus generally, reliable identification depends on close attention to body shape, humeral spot and dentition rather than colour pattern alone.
Morphology
Serrasalmus maculatus has the classic piranha build: a deep, laterally compressed body, a blunt underslung jaw, and a single row of interlocking, razor-edged triangular teeth that shear rather than crush. FishBase records a maximum of 13.5 in total length in females and 10.5 in in males, making this a solidly mid-sized member of the genus — larger than many dwarf Serrasalmus but well short of the biggest black piranhas. Maturity is reached around 4.5 in.
The body carries dark spotting and mottling across silvery flanks, consistent with the "maculatus" (spotted) epithet, though exact pattern and intensity vary with age, mood and population. Sexual dimorphism is minimal; the clearest external cue reported by breeders is that females become noticeably plumper when in spawning condition, but there is no reliable colour or fin difference between the sexes outside that window.
Habitat
The species occurs across the Amazon River basin, the Paraguay-Paraná basin and the Uruguay River, giving it a broad South American range spanning both tropical Amazonian drainages and the more subtropical Paraná-Paraguay-Uruguay system. Within that range it is pelagic and typically encountered in small groups in ponds and creeks with dense marginal vegetation rather than in open river channel.
Because the Paraná-Paraguay-Uruguay portion of its range runs subtropical, water temperatures there are seasonally cooler than in the Amazon proper; aquarium care guides commonly cite a working range of roughly 75–86 °F and pH 5.5–7.5, which is consistent with warm, soft-to-neutral, mildly acidic South American floodplain water rather than extreme blackwater conditions. As with most Serrasalmus, cover — submerged wood, roots and thick vegetation — appears to matter for this naturally cautious, shoal-adjacent fish.
Feeding
Diet shifts with age: juveniles feed mainly on crustaceans and insects, while adults take a mix of fin and flesh scraps from other fish along with substantial scavenging of carrion, consistent with a field study of the species in a Brazilian hydroelectric reservoir that confirmed opportunistic carnivory and scavenging as the dominant natural feeding strategy. This is the pattern typical of Serrasalmus generally — a fin-nipper and flesh-taker more than a fish-killer, with the dramatic "feeding frenzy" behaviour tied to scarcity or a concentrated food source rather than everyday hunting.
In the aquarium, S. maculatus takes fish fillet, frozen fish such as smelt, shrimp, mussel, earthworms, mealworms, insects and quality pellets, and can be weaned onto dead foods without difficulty. Live "feeder" fish should be avoided as a routine diet on general disease and nutrition grounds; the fish will still take live prey opportunistically given the chance, and smaller tankmates are at real risk of fin-nipping or predation.
Mating
Serrasalmus maculatus is a continuous spawner rather than a strict seasonal breeder, though mating activity is reported to coincide with the rainy season, when rising water and increased food availability signal favourable conditions. Ahead of spawning, males establish and defend territories and display to prospective mates; a paired male and female become noticeably more territorial and aggressive around the chosen site, a behaviour FishBase also notes extends into active attacks on intruders once eggs are being guarded.
External sexual dimorphism is minimal outside spawning condition; as in other piranhas, a gravid female typically appears fuller-bodied, and most breeders rely on behavioural cues — territorial pairing, deepening colour, courtship display — rather than fixed physical differences to identify a compatible pair.
Breeding
This is a substrate-spawning egg-layer, not a mouthbrooder or bubble-nest builder. A pair clears and defends a nest site among plants or fine substrate, and the female deposits adhesive eggs that are fertilised and then guarded and fanned at the site, most often by the male. Seriously Fish describes S. maculatus as one of the easier Serrasalmus species to breed in the aquarium, and eggs are reported to hatch within a few days under warm conditions typical of the genus.
Parents — and particularly the guarding male — become markedly aggressive in defence of the nest, to the point of attacking anything that approaches, which is a significant practical consideration for anyone attempting to breed the species in a shared or community setup. As with most Serrasalmus, this is a species best conditioned and spawned in a dedicated tank rather than a mixed display.
In the aquarium
Serrasalmus maculatus is a solitary predator by disposition, and most care guides recommend keeping it alone rather than in a group. Group-keeping is possible but genuinely contested among experienced keepers: some maintain larger groups successfully with heavy cover and generous space, while others report unpredictable aggression and losses, and AquaInfo's guidance reflects that split by calling group-keeping rare and only advisable with real room to spare. A solo specimen needs a minimum tank of roughly 120×17.5 in footprint, while a group setup is recommended at 150×19.5 in or larger plus around 150 additional litres per extra fish, always with dense cover from driftwood, roots or robust planting.
Water should be kept warm (roughly 75–86 °F) with a tolerant pH range around 5.5–7.5 to 6.0–7.8 depending on source, prioritising stability and good oxygenation over chasing an exact number. The jaws are genuinely capable of serious injury, so the fish should be moved by container rather than net, and hands kept clear at feeding time. Tankmates should be limited to species too large or fast to be seen as prey or fin-nipping targets — many keepers simply house the species alone. As with every piranha, check state and local law before acquiring one, since the genus is restricted or outright banned in many U.S. states and countries, and never release a piranha into open water.
Conservation
Serrasalmus maculatus is assessed by the IUCN Red List as Least Concern, consistent with its wide distribution across the Amazon and Paraguay-Paraná-Uruguay basins and its continued presence in the aquarium trade and in regional fisheries studies. It does not currently face the kind of localized, single-river pressure that threatens many narrow-range Neotropical characins.
The clearest open question is taxonomic rather than conservation-status: genetic work has flagged a cryptic species complex within material identified as S. maculatus across separate river basins, which means the "true" range and population picture for this name specifically may be refined as that work matures. General Amazonian and Pantanal-region pressures — damming, deforestation-linked sedimentation and water-quality change — remain long-term watch items for the basins it inhabits, even though the species itself is not currently considered threatened.