Taxonomy & naming
Myloplus lobatus was described by the French ichthyologist Achille Valenciennes in 1850. It sits in the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes, a family that has been heavily revised in recent decades as ichthyologists split the old, broadly defined genus Myleus into several narrower genera. Many silver dollars once listed under Myleus, including this species, are now placed in Myloplus, alongside related genera such as Tometes and Ossubtus; hobby literature and older references may still use the superseded combination "Myleus lobatus," but the Catalog of Fishes (Eschmeyer, California Academy of Sciences) recognises Myloplus lobatus as the valid current name.
Like other silver dollars, M. lobatus is easily confused in the trade with related Myloplus and Metynnis species sold under the same generic "silver dollar" label; positive identification generally rests on fin shape, body proportions and dentition rather than colour alone, none of which are reliably distinguishable from a typical retail tag.
Morphology
Myloplus lobatus has the classic silver dollar profile: a strongly laterally compressed, nearly circular body that gives the group its common name, a small terminal mouth adapted for grazing rather than biting flesh, and a bright, mirror-like silver flank. FishBase records a maximum standard length of 9.5 in for the species, a solidly medium-to-large silver dollar — notably bigger than the small Metynnis species often sold under the same trade name, and a size that should factor into stocking decisions from the outset.
As in most Serrasalmidae, the dorsal profile is deep and the anal fin long-based, and overall body shape converges strongly on that of true piranhas despite the very different diet and temperament — the family's shared "disc with fins" body plan is a hydrodynamic and schooling adaptation, not a sign of shared predatory habits.
Habitat
Myloplus lobatus is native to the Amazon and Orinoco river basins of South America, where it inhabits river channels and, seasonally, the flooded forest and marginal vegetation zones typical of Amazonian floodplain hydrology. Like many Serrasalmidae, it likely follows the seasonal flood pulse, moving into inundated forest to feed on fruit, seeds and submerged vegetation during high water and retreating to main channels and floodplain lakes as water levels fall, though detailed field studies specific to this species are limited.
Water across its native range is generally warm and can vary from soft and acidic blackwater to more moderate clearwater conditions depending on the specific tributary; keepers should aim for stable, warm water in the pH 5–7 range rather than assume a single fixed water type.
Feeding
Myloplus lobatus is a herbivore, grazing on soft aquatic and marginal vegetation, algae, and fallen fruit and seeds in the flooded forest, with the classic phytophagous (plant-eating) dentition documented for the Serrasalminae grazing lineage that includes Myloplus, Tometes and related genera. This is a real ecological role, not an occasional preference — vegetable matter forms the bulk of the natural diet.
In the aquarium this translates directly: offer high-quality herbivorous flake or pellet food plus regular fresh vegetables such as blanched spinach, lettuce, courgette or peas, supplemented with some algae wafers and only modest amounts of protein. Keepers should not expect this species to leave live plants alone — see "In the aquarium" below.
Mating
Detailed courtship behaviour for Myloplus lobatus has not been well documented, either in the wild or in the aquarium; the cached sources describe general silver dollar husbandry rather than species-specific pairing behaviour. As with most Serrasalmidae silver dollars, spawning is thought to be triggered by a rise in temperature and softer, more acidic water conditions that mimic the seasonal flood, consistent with the group's floodplain ecology, but this has not been confirmed specifically for M. lobatus. There is no documented external sexual dimorphism for this species — data is sparse, and keepers should not expect a reliable visual method for sexing individuals.
Breeding
Silver dollars in the genus Myloplus are egg-scatterers: a spawning pair (or group) releases eggs over fine-leaved plants or similarly structured cover, with no nest built and no parental care afterward — the eggs and resulting fry are left to fend for themselves. Reported hobby breeding of this genus is occasional rather than routine, and it is generally associated with soft, acidic water that encourages spawning behaviour.
Species-specific breeding reports for Myloplus lobatus in the aquarium are scarce in the available sources; the general silver dollar pattern above is the best-documented basis for what to expect, but a keeper attempting to breed this particular species should treat the details as provisional rather than proven.
In the aquarium
Myloplus lobatus is a schooling fish and should be kept in a genuine group rather than as a single specimen, in a large aquarium that gives it the open swimming space it uses actively; at a documented maximum of 9.5 in SL, this is not a fish for a small or heavily furnished tank, and adults need serious floor space and volume. A robust, hard-scaped setup — driftwood, rockwork, smooth river stones — suits this species far better than a planted aquascape, because it is a committed plant-shredder that will graze soft-leaved aquatic plants down to bare stems in short order; keepers who want greenery in the tank should stick to tough, unpalatable species or plastic decor.
Water should be kept warm, in roughly the 75–82 °F range with pH around 5–7, with good filtration and stable parameters — silver dollars are active, somewhat skittish fish that do best without sudden changes or excessive handling. Diet should stay vegetable-forward (see "Feeding"), and tankmates should be chosen with the species' size and activity level in mind; despite belonging to the same family as piranhas, M. lobatus is a peaceful community fish when kept in a proper group and is not a fin-nipper or predator.
Conservation
Myloplus lobatus is assessed by the IUCN Red List as Least Concern, reflecting its wide distribution across the Amazon and Orinoco basins and a lack of evidence for significant population decline. As with many widely distributed Amazonian and Orinocan characins, it faces the general long-term pressures affecting the region's freshwater habitats — deforestation, damming and water-quality change — but it is not currently considered threatened, and the cached sources do not indicate any species-specific conservation concern or notable reliance on wild collection for the aquarium trade.