Taxonomy & naming
Cyphocharax nigripinnis was described by Richard P. Vari in 1992, as part of his major systematic revision of the family Curimatidae published in Smithsonian Contributions to Zoology. The holotype, cataloged as MZUSP 42025, is a 2 in standard-length specimen collected from the Rio Xeruini, a tributary within the Rio Branco system in Amazonas state, Brazil. It sits in the genus Cyphocharax, one of several curimatid genera Vari's revision helped stabilize, within the family Curimatidae — the toothless-mouthed detritivorous characins closely allied to Prochilodontidae and Curimatidae's other headwater and floodplain grazers, all under the order Characiformes.
The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the reference point for the genus and species combination used here; there is no indication in available records of a subsequent generic reassignment, so Cyphocharax nigripinnis stands as originally described. The species epithet nigripinnis is straightforward Latin — niger (black) plus pinna (fin) — most plausibly a reference to dark pigmentation on one or more fins noted in the type description, though the cached record does not preserve Vari's original diagnostic wording in enough detail to confirm which fin(s) are meant.
Morphology
Cyphocharax nigripinnis is a small fish by any measure: the holotype measured 2 in standard length, and the species is best treated as reaching roughly 2 in SL at maximum, consistent with the small-bodied end of the genus. Like other Cyphocharax and curimatids generally, it has a fusiform, moderately compressed body, a small subterminal or ventrally positioned mouth without functional teeth, and the generalized silvery countershading typical of small Amazonian shoaling characins — the toothless mouth is the key functional trait distinguishing curimatids from the predatory or plant-shredding serrasalmids covered elsewhere in this atlas.
Detailed meristic and pigmentation data (fin-ray counts, scale counts, the specific dark-fin marking implied by the name) rest in Vari's 1992 original description and are not independently confirmed in the sources available here; this account does not reproduce numbers it cannot verify.
Habitat
The species is known from the Rio Xeruini, a tributary of the Rio Branco within the greater Amazon basin in Amazonas state, Brazil — clearwater-to-blackwater tributary habitat typical of the upper Rio Branco drainage. As a curimatid, it is reasonable to expect the species in slower, soft-bottomed sections of river and tributary channel where fine sediment, submerged wood and leaf litter accumulate, since that is exactly the substrate curimatids graze; but the cached record does not extend beyond the type locality, so broader range and specific microhabitat use should be treated as inferred from family-level ecology rather than documented for this species.
No aquarium-trade or expanded field-survey water-chemistry data is available for this species specifically; general Amazon tributary conditions in this region run warm and soft-to-moderately acidic, but assigning precise figures to Cyphocharax nigripinnis without species-specific data would be guessing.
Feeding
Curimatidae as a family are detritivorous grazers, feeding on the slime film, algae, biofilm and fine organic detritus coating submerged wood, leaf litter and sediment rather than hunting prey or browsing living plant tissue. Cyphocharax nigripinnis, sharing the family's toothless, ventrally oriented mouth, almost certainly follows this pattern, working over surfaces in slow water rather than chasing food in open channels.
No species-specific dietary study or aquarium feeding account is available in the cached record, so this section reflects family-level ecology rather than direct observation of C. nigripinnis.
Mating
No courtship or pairing behavior has been documented for Cyphocharax nigripinnis in the available record. The species is not established in the aquarium trade, and no field or captive breeding account describing spawning behavior, pair formation, or sexual dimorphism could be confirmed from the cache — the honest position is that this remains unrecorded rather than assumed to follow any particular pattern.
Breeding
There is no confirmed breeding record for Cyphocharax nigripinnis, in the wild or in captivity. It is essentially unknown in the aquarium hobby, and unlike the migratory Prochilodus and Semaprochilodus food-fish curimatids or the farmed pacus, there is no indication this species has ever been bred commercially or by hobbyists. Rather than default to a generic open-water egg-scattering mode for the family, this account states plainly that breeding biology for this specific species is undocumented in the sources reviewed.
In the aquarium
Cyphocharax nigripinnis is not a fish anyone will realistically be offered — it does not appear in the aquarium trade, and no aquarium-care account for the species could be confirmed in the cached research (one hobby source that might have covered husbandry was unreachable). Given its small size (around 2 in) and its family's peaceful, grazing habits, a wild-caught specimen turning up as bycatch in a South American tributary shipment would likely suit a quiet, well-planted, soft-water community tank with other small peaceful characins rather than anything resembling the piranha or pacu end of this atlas — but that is an inference from family biology, not a documented care record, and should be treated accordingly.
Conservation
The IUCN Red List assesses Cyphocharax nigripinnis as Least Concern, consistent with a widespread pattern among small Amazon tributary curimatids that lack evidence of population decline or concentrated threats. The species is known from Amazon basin tributary habitat in Brazil that remains largely intact relative to more heavily impacted parts of South America, and there is no record in the cached sources of it being targeted by fisheries or the aquarium trade — its conservation profile is essentially that of an obscure, stable, single-region species rather than one facing active pressure.