Taxonomy & naming
Cyphocharax plumbeus was described by Carl H. Eigenmann and Rosa Smith Eigenmann in 1889. It belongs to the family Curimatidae — the curimatas, a large Neotropical group of small to medium, toothless, deep-grazing characiforms — placing it well apart from the predatory piranhas (Serrasalmidae) and other groups more commonly associated with the "Piranhas & Pacus" umbrella. The genus Cyphocharax comprises dozens of similar-looking, silvery species distinguished mainly by fine details of scale counts, fin-ray formulae and mouth structure, which makes field identification difficult and likely under-recognises the group's true diversity.
The specific epithet plumbeus is straightforward Latin, and the species is best known simply by its scientific name; no established English common name is documented for it in the literature consulted here. As with much of Curimatidae, taxonomic revision within the family is ongoing, and the Catalog of Fishes (Eschmeyer, California Academy of Sciences) remains the reference point for the currently valid combination — retained here as Cyphocharax plumbeus.
Morphology
Cyphocharax plumbeus is a modestly sized, laterally compressed characin reaching a documented maximum of 7 in standard length, per FishBase. Like other curimatids it lacks the interlocking, blade-like teeth of the true piranhas and their pacu relatives — the mouth is small, subterminal to slightly ventral, and adapted for grazing rather than biting, in keeping with the family's detritivorous habit.
Colouration follows the plain, silvery-grey pattern typical of the genus (the epithet plumbeus itself means "lead-coloured"), with a slim, streamlined body built for moving in loose aggregations over sediment rather than for bursts of predatory speed. No distinct sexual dimorphism in body shape or colour is documented for this species.
Habitat
The species is native to the Amazon and Tocantins River basins of South America, where FishBase describes it as a freshwater, benthopelagic fish of tropical lowland systems. It is characteristic of slow-moving water — floodplain lakes, backwaters and vegetated margins — rather than fast, oxygen-rich channels, consistent with the sediment- and biofilm-grazing habit typical of Cyphocharax.
A habitat survey of the Mamirauá Sustainable Development Reserve, in the middle Solimões region of Western-Central Amazonia, recorded water temperatures of 80–89 °F in the floodplain habitats where Cyphocharax species occur, and noted that pH across Amazon streams in the region varies widely — roughly 3.8–4.9 in general blackwater-influenced systems, with the Rio Negro running as low as 3.6–5.8. No pH or hardness figures specific to C. plumbeus itself were found in the sources reviewed; the aquarium-care ranges given below are drawn from a related Cyphocharax species and should be treated as an approximation, not a confirmed figure for this species.
Feeding
Cyphocharax plumbeus is a grazer, not a predator or scavenger of flesh. Curimatids as a family feed on detritus, biofilm, algae and fine organic material sifted from sediment and submerged surfaces, and nothing in the sources reviewed here suggests C. plumbeus departs from that pattern. This places it at the opposite end of the family Characiformes' dietary spectrum from the true piranhas, and closer to the ecological role of the larger migratory grazers such as Prochilodus, though at a much smaller adult size.
Care notes for the related species Cyphocharax multilineatus describe an omnivorous aquarium diet of sinking pellets, flakes and occasional live or frozen foods — a reasonable proxy for feeding C. plumbeus in captivity, though it is not confirmed data for this species specifically.
Mating
No courtship or spawning behaviour has been documented for Cyphocharax plumbeus in the sources available for this account. Curimatids are not a commonly bred aquarium group, and species-specific breeding accounts are correspondingly rare in both the scientific and hobby literature. Nothing here should be read as filling that gap with assumption.
Breeding
Breeding data specific to Cyphocharax plumbeus could not be confirmed from the sources reviewed for this article, and the fishi-pedia care note for the related species C. multilineatus explicitly states that specific breeding data for C. plumbeus was not found in the aquarium literature it surveyed either. In the wild, curimatids and related detritivorous characins are generally understood to be open-water or floodplain egg-scatterers with no parental care, but that pattern is not confirmed for this species and is offered here only as family-level context, not as a documented fact about C. plumbeus.
The species is not known to be bred in the aquarium hobby; it is essentially absent from captive-breeding accounts, and prospective keepers should not expect to reproduce it in a home tank.
In the aquarium
Cyphocharax plumbeus is not an established aquarium trade fish, and no dedicated species-level care guide was found among the sources reviewed. Based on the documented adult size of 7 in SL and the benthopelagic, grazing habits typical of its genus, a keeper attempting this species would need a spacious tank with a soft or fine substrate to graze over, since detritivorous curimatids do poorly when their natural sifting behaviour is denied by coarse gravel or bare glass.
As a proxy only, the related species Cyphocharax multilineatus is documented as tolerating 73–81 °F and pH 5.5–7.5 with hardness around 8–20 dGH, taking pellets, flakes and live foods readily. Those figures are not confirmed for C. plumbeus itself, and given the Amazon floodplain temperatures recorded at Mamirauá (80–89 °F) the real range for this species may run warmer. Like most curimatids it is a peaceable shoaling grazer with no fin-nipping or predatory tendency documented, and would be expected to do best in a group rather than alone, though this too is inference from family-level behaviour rather than species-specific data.
Conservation
The IUCN Red List assesses Cyphocharax plumbeus as Least Concern, an assessment dated 19 October 2020, reflecting its wide distribution across the Amazon and Tocantins basins and the absence of documented major threats. FishBase similarly rates the species as having low vulnerability to fishing pressure (12 out of 100) and medium resilience, with a minimum population-doubling time of 1.4–4.4 years.
As a small, non-predatory grazer with no significant aquarium trade or targeted fishery documented in the sources reviewed, C. plumbeus does not carry the conservation pressures associated with heavily fished or heavily collected characins elsewhere in this atlas. Broader Amazonian pressures — damming, deforestation-linked sedimentation and floodplain habitat change — remain long-term watch items for the basin generally, but nothing in the available sources ties a specific threat to this species.