Taxonomy & naming
Cyphocharax spilurus was described by the English ichthyologist Albert Günther in 1864. It belongs to the family Curimatidae — the toothless characins, a large Neotropical group of detritivorous and algivorous fishes distinguished from their close relatives the Prochilodontidae and Anostomidae by a small, subterminal, near-toothless mouth adapted for sifting fine organic matter rather than grazing algae off surfaces or biting plant material. The genus Cyphocharax itself is large and taxonomically active, with dozens of described species spread across South America, and the Catalog of Fishes (Eschmeyer, California Academy of Sciences) remains the governing authority for which combinations are currently valid within it.
As with many curimatids, C. spilurus is a modestly studied species outside of faunal surveys and museum-based revisions; there is no notable synonymy history captured in the available sources for this account, and the species is best treated here simply under its current combination, Cyphocharax spilurus.
Morphology
Cyphocharax spilurus is a small, laterally compressed characin reaching a documented maximum of about 4 in standard length, well within the modest size range typical of the genus. Like other curimatids it has a somewhat humped dorsal profile, a small, low-set, nearly toothless mouth positioned for feeding along the substrate, and a slender, silvery body built for maintaining position in moving water rather than for speed or predation.
No distinctive colour pattern or fin elaboration is documented for this species in the available sources beyond the plain silver body typical of the genus; it is not a species known for striking markings, and detailed morphometric or colour-pattern description is sparse in the literature available here.
Habitat
Cyphocharax spilurus is native to the coastal river systems of the Guianas, spanning from the Essequibo basin (Guyana) to the Mana River, together with the Cuyuni River shared by Guyana and Venezuela and the upper Rio Branco in Brazil. Within this range it occupies rapids and creeks with sandy or rocky bottoms, the kind of flowing, well-oxygenated stretches typical of Guiana Shield drainages rather than still floodplain water.
Water conditions across its range are tropical and moderately warm, with a temperature range of roughly 68–82 °F and a pH spanning about 6.0–7.8 — slightly acidic to neutral rather than the extreme soft blackwater sometimes assumed for Guiana Shield fish. It is a social, schooling species, consistent with its role as a substrate-grazing shoaler moving over open sand and rock rather than sheltering in dense cover.
Feeding
Cyphocharax spilurus is a bottom-feeding detritivore, consistent with the toothless-mouth body plan shared across Curimatidae. It sifts fine organic material — detritus, biofilm and associated microfauna — from sandy and rocky substrates in the rapids and creeks it inhabits, rather than taking plant matter, algae scraped from hard surfaces, or animal prey in any significant way.
In an aquarium setting this diet translates to sinking foods that reach the substrate: quality bottom-feeder wafers or pellets, blanched vegetable matter and fine particulate foods, offered in a way that lets a shoal work the tank floor as it would a riverbed. Data on captive feeding response specific to this species is limited, so this follows from its documented wild diet and the general husbandry pattern for detritivorous curimatids rather than direct aquarium reports.
Mating
Available sources do not document courtship behaviour, pairing, or sexual dimorphism for Cyphocharax spilurus. FishBase notes that the species spawns during the rainy season in flooded areas, which places it among the many Neotropical characins whose reproduction is tied to seasonal flood-pulse hydrology rather than year-round or aquarium-triggered spawning, but no detail on courtship display or mate selection is available in the cache for this account. Data sparse — no external sexual dimorphism is documented for this species.
Breeding
Cyphocharax spilurus is a seasonal spawner tied to the rainy-season flood pulse, spawning in flooded areas rather than at a fixed nest site — a pattern shared with many curimatids and other floodplain-dependent Neotropical characins, and distinct from the substrate-nesting behaviour of true piranhas or the farmed, hormone-induced spawning of the large migratory food-fish characins. No parental care is documented, consistent with the broadcast-spawning pattern typical of the family.
This species is not established in the aquarium trade and there are no documented accounts of it being bred in captivity. Given its reliance on seasonal flooding as a spawning cue, captive breeding would likely be difficult to replicate without simulating that flood-pulse trigger, but this is inference rather than a documented outcome — no aquarium breeding reports exist in the sources available for this account.
In the aquarium
Cyphocharax spilurus is not a fish with an established aquarium presence, but the available notes describe it as suitable for aquaria when it is available: a peaceful, schooling bottom-feeder that should be kept in a group rather than singly, over a sandy or rocky substrate that lets it forage naturally. No aggression or fin-nipping behaviour is noted for the species, which fits its detritivorous feeding mode and sets it apart from the piranha reputation that dominates this family's public image.
A modest adult size of around 4 in means this is not a fish that will outgrow a reasonably sized community tank the way a pacu or a large predatory characin would; the practical challenge for a prospective keeper is more likely to be sourcing the species at all, since it has no meaningful footprint in the ornamental trade. Warm, slightly acidic to neutral water in the range documented for its native range, good water flow, and a sifting substrate are the relevant husbandry notes drawn from its natural history.
Conservation
Cyphocharax spilurus is assessed as Least Concern by the IUCN Red List, an assessment dated 19 October 2020. The Red List notes that no species-specific conservation actions are directed at it and that taxonomic certainty within the genus is limited, with more data needed on the species' precise distribution and any threats it may face.
Its range across the Guiana Shield's coastal rivers and the upper Rio Branco has historically seen comparatively lower habitat pressure than more heavily developed parts of South America, though the Least Concern status reflects an assessment based on limited targeted study rather than an exhaustive population survey. There is no indication in available sources that the species is targeted by the aquarium trade or by fisheries at any scale that would affect its conservation status.