Taxonomy & naming
Mylossoma aureum was described by Johann Baptist von Spix and Louis Agassiz in 1829, part of the same expedition-era body of work that produced early descriptions of many Amazonian fishes collected during Spix's Brazilian travels. It belongs to the family Serrasalmidae — piranhas, pacus and silver dollars — within the order Characiformes, and to the genus Mylossoma, a small group of deep-bodied, round-toothed pacu relatives that the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises as distinct from the larger food-fish pacu genera Colossoma and Piaractus and from the true silver dollars now placed in Myloplus and related genera following the split of the old, broadly defined Myleus.
In the aquarium trade Mylossoma aureum is very commonly sold simply as "silver dollar," a name it shares loosely with several other deep-bodied serrasalmids, and the trade name "golden pacu" adds further confusion by implying a relationship to Piaractus brachypomus, the true pacu food-fish. The genus name Mylossoma is retained here as the valid combination; no correction or resplitting of this particular species is indicated by the available record.
Morphology
Mylossoma aureum has the classic serrasalmid "dollar" shape: a strongly laterally compressed, disc-like body, a small head, and a long-based, sickle-shaped anal fin typical of the family. FishBase records a maximum published length of 8 in total length for the species, modest by pacu standards but still a substantial, deep-bodied fish once mature — nothing like the tiny juveniles sold in shops.
The defining feature that separates it from a true piranha at a glance is the dentition: rather than a single row of interlocking, triangular cutting teeth, Mylossoma aureum carries rows of blunt, rounded, molar-like teeth adapted for crushing hard seeds and fruit rather than shearing flesh. Colouration is a bright, often golden-tinged silver overall, which is very likely the basis for the "golden pacu" trade name, though the cache does not document a formal description of fin colouration or any reliable field marks beyond general body shape and size.
Habitat
Mylossoma aureum is native to the Amazon and Orinoco river basins, with documented occurrence records spanning Bolivia, Brazil, Colombia, Ecuador, Peru and Venezuela, including the Japurá River. FishBase describes the species as benthopelagic and potamodromous — an active migrant within fresh water rather than a sedentary resident — occupying tropical freshwater habitats across this very wide South American range.
Recorded water conditions sit in a broad tropical band of roughly 72–82 °F. The cache does not provide specific pH or hardness figures for this species; given its potamodromous, floodplain-linked biology it likely experiences the same seasonal swings between whitewater, clearwater and blackwater conditions typical of the Amazon and Orinoco systems, but that should be treated as inference from the wider basin rather than a documented figure for this species specifically.
Feeding
FishBase characterises Mylossoma aureum as an omnivore with a marked tendency toward herbivory, taking vegetal matter alongside invertebrates. This fits the wider pacu pattern of seed- and fruit-eating in flooded forest during high water, using blunt molariform teeth to crush hard plant material that many other fish cannot process — a role that makes pacu-group fishes important seed dispersers across their range, though the cache does not document a specific dispersal study for this species.
In the aquarium this diet translates directly: a varied, plant-forward menu of vegetables, fruit and quality pellets, supplemented with some protein, mirrors the wild pattern far better than a meat-heavy or feeder-fish-based diet. Keepers should expect the blunt crushing teeth to make short work of tough foods that soft-toothed community fish cannot manage.
Mating
FishBase notes that Mylossoma aureum undertakes reproductive migrations, moving to spawn during the flood season in white-water rivers and associated wetlands — the same long-distance, flood-pulse-triggered migratory pattern documented for the larger pacu genera. No pairing behaviour, courtship display or external sexual dimorphism is documented in the cache for this species; migratory serrasalmids of this kind typically spawn in aggregations rather than forming discrete pairs, but that detail is not confirmed here and should not be assumed.
Breeding
Mylossoma aureum is a migratory food-fish in reproductive terms, not a home-aquarium breeder. FishBase describes it as undertaking flood-season reproductive migrations into white-water rivers and wetlands, releasing large numbers of eggs broadcast into open water; the species is described as highly fecund and fast-growing, with correspondingly high early-life mortality typical of a broadcast-spawning migratory strategy. This is the same reproductive pattern documented for its larger relatives Colossoma and Piaractus, which are farmed and hormone-induced (via hypophysation) for spawning at commercial aquaculture scale across South America.
The cache does not document any hobbyist or commercial home-aquarium spawning of Mylossoma aureum specifically, and given the migratory, flood-pulse-dependent nature of its reproduction, it should be considered essentially unbred in captivity outside of large-scale aquaculture contexts. Prospective keepers should not expect to breed this species in a home tank.
In the aquarium
Mylossoma aureum reaches roughly 8 in total length — a genuinely deep-bodied, disc-shaped fish once grown, even though it stays well short of the metre-plus size of the giant food-fish pacus. It should still be housed with real swimming room: a large, long aquarium with strong filtration to handle its bioload and a robust diet of vegetables, fruit and pellets, matching the omnivorous-to-herbivorous diet documented on FishBase.
Like other serrasalmids in the pacu and silver-dollar group, it is typically kept in company rather than alone, and its blunt but powerful crushing jaws mean that soft-leaved aquarium plants are at real risk of being shredded — plan on tough, unpalatable or artificial plantings rather than a heavily planted display. As with any Neotropical fish of this family, it should never be released into local waterways if a keeper can no longer accommodate it; feral pacu-group fish are a documented invasive concern in several regions outside their native range.
Conservation
The IUCN Red List assesses Mylossoma aureum as Least Concern, with an assessment dated 21 December 2020, reflecting its very wide native distribution across the Amazon and Orinoco basins (spanning Bolivia, Brazil, Colombia, Ecuador, Peru and Venezuela) and no immediate documented threat to the species as a whole.
The cache does not document specific fisheries pressure, habitat threats or trade-collection data for this particular species beyond its wide range and stable LC status. Broader pressures on Amazon and Orinoco freshwater systems — damming, deforestation-linked sedimentation and water-quality change — are relevant long-term watch items across this range generally, though none are documented in the cache as specific to Mylossoma aureum.