Taxonomy & naming
Cyphocharax muyrakytan was described in 2018 by Bortolo, Lima and Melo in the journal Copeia (106(2):346–352), one of many recent additions to a genus that has expanded considerably as Amazonian curimatids have been re-examined river system by river system. It belongs to the family Curimatidae — the toothless, detritivorous "curimatas" — within the order Characiformes, a family that, along with Hemiodontidae, Prochilodontidae and the pacu- and piranha-bearing Serrasalmidae, makes up the broader assemblage of non-tetra characins covered here.
The species epithet muyrakytan derives from the Tupi word muyrakyta, referring to the muiraquitã — a small amulet carved in the shape of a sitting frog from green stone (often nephrite or jade), traditionally associated with the extinct Tapajó culture that once inhabited the lower Tapajós region where the type series was collected. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the reference point for the validity of the name; as a 2018 description with no subsequent synonymy noted in available sources, Cyphocharax muyrakytan stands as currently accepted.
Morphology
Cyphocharax muyrakytan is a small fish even by the standards of its genus, with a maximum recorded standard length of 2 in. The original description characterises the body as light-coloured with an overall silvery hue, lacking the dark longitudinal stripes, blotches or humeral spots that mark many congeners and relatives, and it carries a distinctly straight body profile — a feature the describing authors used, along with other meristic and morphometric details, to separate it from similar-looking Cyphocharax species in the same drainage.
Like other curimatids, it almost certainly shares the family's toothless, protrusible mouth adapted for grazing organic material and fine sediment from surfaces rather than biting prey, though the original description's full morphological detail was not available in the sources consulted here. No published account of external sexual dimorphism exists for this species.
Habitat
The species is known only from the lower Rio Tapajós and its Rio Arapiuns tributary, both clearwater systems draining into the Amazon in the Brazilian state of Pará. FishBase lists its habitat as floodplain tributaries — benthopelagic, freshwater and tropical — consistent with the general ecology of small Curimatidae, which typically occupy slower-flowing, vegetated or sediment-rich margins of Amazonian rivers and their seasonally flooded tributaries rather than open river channel.
No specific temperature or pH data for this species were located in the sources consulted; the lower Tapajós and Arapiuns are clearwater tributaries of the Amazon, generally warm and circumneutral, but a keeper or researcher should not assume precise parameters without further documentation, and none is asserted here.
Feeding
No diet study specific to Cyphocharax muyrakytan was found in the sources reviewed for this article. Curimatidae as a family are characteristically toothless detritivores and biofilm grazers, feeding by sifting fine organic sediment and algal film from surfaces rather than taking discrete prey items, and the small size and generalist body plan of C. muyrakytan are consistent with that pattern. This should be read as an inference from family-level biology rather than a documented fact for this particular species; data on its actual gut contents or foraging behaviour is sparse to nonexistent in the available literature.
Mating
Nothing has been published on courtship or pairing behaviour in Cyphocharax muyrakytan. The species was described in 2018 from preserved museum material and has not, as far as the sources consulted show, been kept or observed alive in captivity, so there is no aquarium or field account of spawning behaviour to draw on. No sexual dimorphism has been documented.
Breeding
Breeding biology for Cyphocharax muyrakytan is undocumented. It has not been established in the aquarium trade, and the sources consulted found no captive-breeding reports, hormone-induced spawning records, or field observations of reproduction for this specific species. Many small Curimatidae are presumed to be open-water or scatter-spawners typical of the broader characin group, but that mode has not been confirmed for C. muyrakytan itself, and this article does not assign one. This is a clear case where the honest answer is that the biology is simply not yet known.
In the aquarium
Cyphocharax muyrakytan is not an aquarium fish. It was described only in 2018 from a restricted stretch of the lower Rio Tapajós and Rio Arapiuns, it does not appear in the ornamental trade, and no husbandry information — tank size, water chemistry, tankmates, feeding regime — has been published or observed for it. Any care guidance offered for this species would be invented rather than documented, so none is given here. If it is ever collected for the hobby, its very small adult size (around 2 in) and its relatives' schooling, detritivorous habits suggest it would suit a peaceful, planted community rather than anything resembling piranha- or pacu-style care, but this is inference from the genus, not a confirmed account of the species.
Conservation
Cyphocharax muyrakytan is assessed by the IUCN Red List as Endangered (EN), with the assessment dated 23 November 2020 and applied under criteria B1ab(iii)+2ab(iii) — indicating a very restricted geographic range combined with an observed or projected decline in the extent or quality of its habitat. That restricted range is precisely the lower Rio Tapajós and Rio Arapiuns, an area that has faced mounting pressure from damming, deforestation-linked sedimentation, mining and agricultural expansion across the wider Tapajós basin in recent years.
Because the species is known from so narrow a range and has no presence in the aquarium or food-fish trade, its conservation outlook rests entirely on the health of that specific stretch of river system rather than on any collection pressure. It is a useful reminder that many recently described Amazonian characins carry real, documented extinction risk despite being essentially unknown outside the primary taxonomic literature.