Taxonomy & naming
Myloplus schomburgkii was described by the Scottish naturalist William Jardine in 1841 and has long circulated in the aquarium trade under the older combination Myleus schomburgkii, a name still used by several retailers and care-sheet sites. It belongs to the family Serrasalmidae — the piranhas, pacus and silver dollars — within the order Characiformes. Serrasalmidae taxonomy has been revised substantially in recent decades: the old, broad genus Myleus was split, and many of its silver-dollar-type species, including this one, were moved into Myloplus. GBIF lists the current valid combination as Myloplus schomburgkii (Jardine, 1841), and that is the name used here.
Aquarium sources caution that more than one species may be circulating under the name M. schomburgkii, since populations from different river systems show geographic variation in body proportions and colour intensity; a formal taxonomic review may eventually split the name further. The species is also frequently confused in the trade with the redhook myleus, Myloplus rubripinnis, which shares a similar disc shape but lacks the diagnostic black vertical bar.
Morphology
Like other Serrasalmidae in the silver-dollar lineage, M. schomburgkii has a strongly laterally compressed, near-circular "disc" body shape, a small terminal mouth and a dorsal fin set well back on the body. Its most distinctive field mark is a broad black vertical bar crossing the mid-flank, set against a body that ranges from bright silver to warm gold depending on age, mood and population — a pattern that gives rise to its common names (black-barred silver dollar, black-band myleus). A dark spot near the gill cover (the "black ear" of one common name) is also frequently present.
Reported adult size varies widely between sources: SeriouslyFish gives a conservative maximum standard length of around 4.5 in, while other accounts, including FishBase-derived figures, put wild adults at 16.5–17.5 in. This is an unusually wide spread even for a variable species, and it likely reflects a combination of measurement type (standard length versus total length), population variation, and possibly more than one species being reported under the same name. Prospective keepers should plan around the larger, well-supported figure rather than assume the fish will stay small. As in other serrasalmids, mature males develop a two-lobed anal fin, a feature used to sex adult fish (see "Mating").
Habitat
Myloplus schomburgkii is native to northwestern and central South America, recorded from the middle and lower Amazon River basin, the Nanay River, and the upper Orinoco River basin, spanning Brazil, Peru and Venezuela, with a possible presence in Suriname. Within this range it inhabits tropical river channels and associated floodplain habitat typical of lowland Amazonian and Orinocan drainages.
Water across its range is generally warm and on the soft, slightly acidic side: cited parameters run roughly 23-27 degrees Celsius, pH 6.0-7.0, with hardness up to about 10 degrees H. These are moderate, not extreme, blackwater conditions, and they are broadly consistent with the wider pattern of soft, mildly acidic Amazonian tributary water rather than the very low pH and near-zero hardness seen in the darkest blackwater systems.
Feeding
M. schomburgkii is fundamentally herbivorous, and every source consulted agrees on this point: despite its close kinship with the piranhas, this fish is a plant-and-algae grazer, not a predator. In the aquarium it needs a diet dominated by vegetable matter — blanched courgette (zucchini), cucumber, peas, leafy greens, algae wafers and spirulina-based foods — supplemented with a smaller amount of protein such as bloodworm or brine shrimp.
The practical consequence for keepers is that this species will not coexist with live aquarium plants; a hungry group of silver dollars can strip a planted tank to bare stems in short order. Its jaws and dentition, while adapted for grazing rather than hunting, are described as capable of a surprisingly painful bite, so careful handling is warranted even though the fish is not aggressive toward tankmates in the way a true piranha can be.
Mating
Documentation of courtship behaviour in M. schomburgkii itself is sparse. The clearest sexing cue reported across serrasalmid silver dollars, including this species, is that mature males develop a two-lobed (bilobed) anal fin as they reach breeding condition, a trait absent or far less pronounced in females. Beyond this anatomical marker, specific pairing or courtship behaviour for M. schomburgkii is not documented in the sources reviewed here, and this article does not speculate beyond what is recorded.
Breeding
Myloplus schomburgkii is, by the pattern typical of silver dollars in this family, an egg-scatterer that spawns over fine-leaved aquatic plants, with no parental care of eggs or fry once spawning is complete. Reports on captive breeding of this exact species are conflicting: at least one aquarium source states there are no documented captive breeding reports for M. schomburgkii specifically, while accounts of related silver-dollar species describe successful spawns in soft, acidic water (roughly KH 4-8, 27-28 degrees Celsius) producing very large clutches of 1,500-2,000 eggs that hatch in about three days, with fry free-swimming within roughly a week.
Given the conflicting picture, keepers should treat M. schomburgkii as a species that is, at best, only occasionally bred in the home aquarium, and should not expect the reliable, repeatable spawns seen in some other characins. Set up correctly — soft, acidic, warm water and a well-conditioned group — a spawn is plausible by analogy with its close relatives, but it is not something to count on.
In the aquarium
This is a shoaling fish that should be kept in a group, and tank size needs to be planned around its larger reported adult size rather than the more optimistic 4.5 in figure: juveniles can be housed in a four-foot aquarium, but mature fish are best given a minimum of roughly six feet in length by two feet in width and depth. Given this size trajectory, M. schomburgkii is not a fish for a modest community tank — it needs serious long-term space.
Because it is a determined plant-eater, this species belongs in a robust, hard-scaped setup with driftwood and rockwork rather than a planted aquascape; any live plants offered will most likely be eaten rather than decorative. Diet must be vegetable-forward (see "Feeding"), and strong filtration is warranted given the fish's adult bulk and appetite. Despite its herbivorous diet, handle with care: its bite is reported as capable of causing real pain, so use a container rather than bare hands when moving it.
Conservation
Myloplus schomburgkii has not been formally assessed by the IUCN Red List and currently carries a status of Not Evaluated. This is a common situation for Serrasalmidae species outside the handful of large, heavily fished or farmed pacus, and it does not by itself indicate any particular level of concern or scarcity — it simply means no full Red List assessment has been published.
No specific population pressures are documented in the sources reviewed for this article. As with many mid-sized Amazonian and Orinocan characins, general watch items for the wider region include habitat pressure from damming, deforestation-linked sedimentation and water-quality change, though none of this is documented specifically for M. schomburgkii.