Taxonomy & naming
Mylossoma duriventre was described by Georges Cuvier in 1818 as Myletes duriventris, one of the earliest formally named members of the pacu-and-silver-dollar assemblage that would later be split into the modern genera of family Serrasalmidae. It sits in the genus Mylossoma, a small group of laterally compressed, herbivorous-to-omnivorous characins distinguished from the true piranhas (Pygocentrus, Serrasalmus) by their molariform crushing teeth rather than blade-like cutting teeth, and from the pacus proper (Colossoma, Piaractus) by their smaller adult size and more discoid body shape.
Serrasalmidae has undergone heavy taxonomic revision in recent decades, with silver-dollar lineages formerly lumped under genera such as Myleus split out into Myloplus, Tometes and Ossubtus, and pacu lineages separated from Colossoma. Mylossoma itself has remained comparatively stable, but a 2018 taxonomic revision restricted the name Mylossoma duriventre, in the strict sense, to populations of the Paraná-Paraguay-Uruguay basin, with related Amazonian and Orinoco populations sometimes referred to this species in older literature but treated with more caution today. The common names "silver mylossoma" and "silver dollar" both describe its flattened, coin-like silver profile, though the latter name is shared loosely across several genera in the family and is not a reliable identifier on its own.
Morphology
Mylossoma duriventre has the classic silver-dollar build: a strongly compressed, almost circular to oval body, a small head, and a short-based dorsal fin set well back, giving it a disc-like silhouette in the water. FishBase records a maximum length of about 10 in standard length and a maximum weight around 1 kg, modest by the standards of its pacu relatives. The body is bright silver overall, often with a faint olive or yellowish cast on the back and clear to lightly dusky fins; the anal fin base is notably long, a feature shared across the genus.
The mouth is small and set with rows of blunt, molar-like teeth adapted for crushing seeds, nuts and plant material rather than slicing flesh — a key distinguishing feature from the sharp-toothed true piranhas with which serrasalmids are sometimes lazily grouped in the popular imagination. There is no reliably documented external difference between the sexes in this species.
Habitat
Mylossoma duriventre inhabits river channels, floodplain lakes and seasonally inundated forest within its native range, with the strict taxonomic sense of the species now understood to be centred on the Paraná-Paraguay-Uruguay basin of South America; related populations occur more broadly across Amazonian and Orinoco drainages. FishBase describes it as a freshwater, benthopelagic species that is potamodromous — it migrates within river systems, timing its movements to the flood pulse and depending on seasonally flooded forest and floodplain habitat for feeding and, most likely, spawning.
Water conditions across its range are warm and span soft to moderately hard water, with FishBase citing a temperature range of roughly 72–82 °F, a pH range of about 5.0–7.8, and hardness up to 20 dH — a wider tolerance than the narrow blackwater stereotype often assumed for Amazonian characins. As a floodplain species, it relies on the seasonal rise and fall of river levels, moving into flooded forest to feed on fallen fruit and seeds during high water and retreating to the main river channel and connected lakes during the dry season.
Feeding
Mylossoma duriventre is a frugivore-leaning omnivore. FishBase assigns it a trophic level around 2.8, consistent with a diet built substantially around plant material — chiefly seeds and fruit that fall into the water from the flooded forest canopy — which the fish crushes with its blunt, molar-like teeth. In this role it functions as a seed disperser within its floodplain ecosystem, swallowing and later passing seeds from fruiting trees during the high-water season, a pattern well documented across the pacu-and-silver-dollar lineages of Serrasalmidae more broadly.
Some sources note that related serrasalmids will also take insects, small invertebrates and other incidental animal matter, so the diet should be considered omnivorous with a strong plant bias rather than strictly herbivorous. In the aquarium it is an easy feeder, taking a varied diet of vegetables, fruit, sinking pellets and flake, with occasional protein such as bloodworm or brine shrimp; a plant-forward diet best matches its natural feeding ecology.
Mating
Detailed courtship behaviour for Mylossoma duriventre is not well documented in the available literature. What is established is that the species is potamodromous, meaning reproduction is tied to river migration rather than to a fixed territorial pairing behaviour of the kind seen in substrate-spawning piranhas. Spawning is understood to be linked to the seasonal flood pulse, with adults moving within the river system as water levels rise, a pattern shared with its pacu relatives and with the migratory characin fisheries of South American rivers generally.
No external sexual dimorphism has been documented for this species; sexes cannot be reliably distinguished by colour or body shape from available sources.
Breeding
Mylossoma duriventre is a migratory floodplain spawner, not a species that breeds in the home aquarium. Like its larger pacu relatives, it times reproduction to the flood pulse, and where it is propagated at all this is done commercially, at fish-farm scale, typically using hormone-induced spawning protocols rather than natural pairing in captivity — the same approach used for large-scale aquaculture of related Serrasalmidae. There is no meaningful hobbyist track record of home breeding for this species, and prospective keepers should not expect to spawn it in a home tank.
Eggs and early development have not been documented in the sources available here; what can be said with confidence is that reproduction depends on the seasonal hydrology of its native floodplain systems, a life-history pattern that simply does not translate to static aquarium conditions.
In the aquarium
Mylossoma duriventre is one of the more forgiving members of the pacu-and-silver-dollar family for a home aquarist, precisely because it stays comparatively small — a published maximum around 10 in rather than the near-metre size of true pacus. It is nonetheless a shoaling, active swimmer that should be kept in a group in a large, long aquarium with open swimming space, and its disc-shaped, bright-silver body makes it an attractive, easy-care fish once given adequate room; aquarium-trade sources describe it as popular for exactly this combination of good looks and undemanding care.
Because it feeds heavily on plant material in the wild, it should be expected to graze soft aquarium plants, so keepers should plan around tough, unpalatable or artificial vegetation rather than a delicate planted layout. Water should be kept warm, in the roughly 72–82 °F range documented on FishBase, with soft-to-moderately-hard water and a pH from about 5.0 up to nearly neutral-to-slightly-alkaline conditions; strong filtration is worthwhile given its active swimming and plant-heavy diet. As with all Serrasalmidae, this is a South American floodplain native and should never be released into local waterways.
Conservation
Mylossoma duriventre is assessed by the IUCN Red List as Least Concern, reflecting its wide distribution across South American floodplain systems and no evidence of significant population decline. It is a comparatively minor and lightly documented species relative to its more heavily fished and farmed pacu relatives, and specific threat data tied to this species alone is sparse in the sources available here.
As a floodplain-dependent, migratory species, it shares the general long-term pressures facing South American river fish across its range — damming and altered flood hydrology, deforestation of floodplain forest that supplies its seed-and-fruit diet, and water-quality change — even though none of these currently push the species into a threatened category.