Taxonomy & naming
Cyphocharax sanctigabrielis was described by Marcelo Rodrigues de Melo and Richard P. Vari in 2014, in a paper published in the Brazilian journal Zoologia (SciELO). It belongs to the family Curimatidae, one of several detritivore-heavy families — alongside Prochilodontidae, Anostomidae and their relatives — that make up the quiet, algae- and sediment-grazing side of Characiformes, standing in obvious contrast to the predatory Serrasalmidae piranhas that dominate the popular idea of a "characin." The genus Cyphocharax is large and still actively revised, and the Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for which combination is currently valid; nothing in the cited literature suggests this species has been moved out of Cyphocharax since its description.
The species epithet sanctigabrielis is a Latinised reference to São Gabriel da Cachoeira, the Amazonas municipality on the upper rio Negro nearest the type locality — a naming convention common among characins described from a single well-documented site rather than a wide range. As a species described only in 2014 from a handful of specimens, it has no vernacular or trade name; it is known solely by its scientific name.
Morphology
The type series described by Melo and Vari ranges from 1.5–2.5 in standard length (roughly 1.5–2.5 in), with the holotype measuring 2.5 in SL — a small fish even by the modest standards of the curimatid grazers. No detailed account of colouration, fin counts or other diagnostic morphology beyond the original taxonomic description is available in the sources consulted here, and this article does not attempt to reconstruct one from memory. What is documented is size: this is not a fish that grows to anything resembling piranha, pacu or even silver-dollar scale — it stays firmly in the small-headwater-characin bracket.
Habitat
Cyphocharax sanctigabrielis is known only from Igarapé Nouba Uba, a small blackwater stream in the upper rio Negro drainage near São Gabriel da Cachoeira, Amazonas, Brazil (type locality approximately 00°00.321′N, 66°55.357′W). The species appears to be restricted to the upper rio Negro above its rapids, a zone that isolates the fish fauna there from the main river below — a pattern seen in a number of upper-Negro headwater endemics.
The type locality is a shallow, slow-flowing forest stream over fine sand, and the water is extreme blackwater in the classic upper rio Negro style: tea-dark, tannin-stained, very soft and acidic, with pH recorded between 3.6 and 5.8 and very low mineral content and conductivity. This places it among the most acidic water conditions documented for any fish in this atlas, and it should not be generalised to other Cyphocharax or curimatid species without their own sourcing.
Feeding
No diet study specific to Cyphocharax sanctigabrielis is available in the sources consulted. The genus Cyphocharax as a whole, and the family Curimatidae generally, are characteristically detritivore-omnivore grazers, feeding on organic sediment, biofilm and algae scraped from submerged wood, sand and leaf litter rather than hunting live prey — the opposite ecological role from the piranhas and dorado that share this atlas's broader "Piranhas & Pacus" grouping. It is reasonable to expect this species follows that family-wide pattern given its small size and blackwater headwater habitat, but that inference is not a documented fact for this species specifically, and no aquarium feeding data exists because the species is not established in the trade.
Mating
No courtship or spawning behaviour has been documented for Cyphocharax sanctigabrielis. The original description is a taxonomic account based on preserved museum material and does not report field observations of reproductive behaviour, and no subsequent study appears to have filled that gap. Nothing is known of sexual dimorphism in this species either — the type series was not described with distinguishing male/female characters in the sources reviewed here.
Breeding
There is no published breeding record for Cyphocharax sanctigabrielis, in the wild or in captivity. The species has never been kept or bred in the aquarium hobby to any documented extent, and this account will not assign it a breeding mode by inference from relatives — unlike the true piranhas (nest-guarding substrate spawners) or the silver dollars (egg-scatterers), curimatid reproduction in general is comparatively poorly documented even at genus level. The honest state of knowledge is simply: unknown.
In the aquarium
Cyphocharax sanctigabrielis has no aquarium history. It is not collected or traded, was only described in 2014 from a remote upper rio Negro headwater stream, and there are no husbandry reports to draw on. Given its small size (under 3 in) and its extreme, very soft, very acidic blackwater origin, any speculative care would need to mirror true upper-Negro blackwater conditions — heavy tannin staining, minimal mineral content, low pH — but that is an inference from habitat data, not a tested aquarium record, and this species should not be presented as an available or recommended aquarium fish.
Conservation
Cyphocharax sanctigabrielis has not been evaluated by the IUCN Red List and carries a Not Evaluated (NE) status; no search of the Red List returns a species-specific assessment. This is unsurprising for a species described as recently as 2014 from a single stream system, and it should not be read as reassurance — a fish known from one small headwater tributary above the rio Negro rapids is inherently exposed to any single-site pressure (local land-use change, mining-related water quality impacts, or hydrological disruption) even though none has been specifically documented against this species. As with many recently described, narrow-range upper-Negro endemics, the honest summary is that its conservation status is simply unassessed rather than confirmed safe.