Taxonomy & naming
Cyphocharax naegelii was described by the Austrian ichthyologist Franz Steindachner in 1881. It belongs to the family Curimatidae — the "toothless characins" or curimatas — within the order Characiformes, a family distinguished from the piranhas, pacus and silver dollars of Serrasalmidae by the near-total absence of functional jaw teeth and a gut adapted to processing fine organic material rather than flesh or plant matter. The genus Cyphocharax is one of several curimatid genera (alongside Curimata, Steindachnerina and Psectrogaster) recognised by the Catalog of Fishes (Eschmeyer, California Academy of Sciences) as the current authority for valid names in the family.
Curiculatid taxonomy has been repeatedly revised as museum collections and molecular work sort out a family whose species are notoriously similar in external appearance — deep-bodied, silvery and largely field-indistinguishable without close examination of mouth position and scale counts. C. naegelii is known with confidence from the Upper Paraná basin in Brazil; no reliable common name has become established for it in English-language sources, hobby or otherwise, which itself reflects how far outside the aquarium trade this species sits.
This fish was long listed as Cyphocharax nagelii; Eschmeyer's Catalog of Fishes now treats that name as a synonym of Cyphocharax naegelii, the valid name followed here.
Morphology
Like other Curimatidae, Cyphocharax naegelii has a moderately deep, laterally compressed, silvery body typical of a mid-water-to-bottom-foraging characin, with a small, subterminal or ventrally positioned mouth suited to browsing surfaces rather than biting prey. The jaws lack the functional dentition seen in predatory or omnivorous characins; feeding is accomplished instead with pharyngeal structures adapted to processing detritus, algae and fine organic sediment, a hallmark of the family.
FishBase records a maximum published length of 7.5 in total length for the species, with specimens up to 9 in TL recorded in Brazilian field studies and a maximum recorded weight of about 90 g. That places C. naegelii solidly among the larger curimatids — a substantial, plainly built river fish rather than a small tetra-sized shoaler.
Habitat
Cyphocharax naegelii is documented from the Upper Paraná River basin in Brazil, part of the broader Paraná-Paraguay drainage that runs through the subtropical southern reaches of South America rather than the equatorial Amazon. Curimatids in this basin are typically found in main river channels and their floodplain-connected habitats, where they graze detritus and algae from submerged surfaces and soft substrate.
Specific water-chemistry data for C. naegelii is sparse in the sources available. As an Upper Paraná basin species, it inhabits the cooler, more seasonal subtropical waters characteristic of that drainage rather than the warm, stable conditions typical of Amazonian blackwater — a distinction worth flagging for anyone extrapolating generic "South American characin" care parameters onto it.
Feeding
Cyphocharax naegelii is an omnivorous grazer in the mould of the Curimatidae generally: FishBase and family-level accounts describe the group as feeding on detritus, algae, biofilm and fine organic sediment scraped or sifted from submerged surfaces and the riverbed, rather than hunting live prey or taking large food items. This toothless, browsing feeding mode is the defining ecological trait of the family and the reason curimatids are informally called "toothless characins."
No aquarium feeding record specific to this species is documented in the sources available; by analogy with related Cyphocharax species kept occasionally in the hobby, a detritivore/omnivore diet of algae wafers, blanched vegetables, and fine sinking foods would be the expected approach, but this is inference from the genus rather than a confirmed record for C. naegelii itself.
Mating
No courtship or pairing behaviour specific to Cyphocharax naegelii is documented in the sources available. Data is sparse to the point that even basic reproductive biology — spawning triggers, aggregation behaviour, or seasonal timing — is not established for this species in the literature consulted here.
Breeding
Breeding for Cyphocharax naegelii is not documented in the sources available, and the species has no established aquarium-breeding record. A related congener, C. multilineatus, is noted in aquarium literature as an egg-scatterer occasionally spawned in soft, acidic water among fine-leaved vegetation with no parental care, which is consistent with the general Curimatidae pattern of open-water or substrate egg-scattering without brood care. Whether C. naegelii follows the same pattern has not been confirmed, and no record of it being bred in the aquarium hobby exists in the sources reviewed — this account states that gap rather than assuming egg-scattering applies here by default.
In the aquarium
Cyphocharax naegelii is essentially absent from aquarium literature; the sources available describe fisheries and museum-taxonomy data, not tank-keeping experience. What can be said with confidence is scale: at up to 7.5–9.1 in TL, this is a substantial river fish, considerably larger than the small tetras most hobbyists associate with Neotropical characins, and any prospective keeper should plan tank size around that real adult length rather than around unrelated smaller species in the same order.
As a detritivorous grazer from a cooler subtropical basin, C. naegelii would be expected to want a large, well-filtered aquarium with a sifting substrate and a varied diet of algae- and detritus-based foods, kept in a shoal as is typical for Curimatidae in the wild — but this is a reasonable inference from its biology and family, not a documented hobby account. There is no basis in the available sources for stocking, tankmate or breeding advice specific to this species.
Conservation
The IUCN Red List assesses Cyphocharax naegelii as Least Concern, with an assessment dated November 7, 2018. This reflects the species' presence in a well-studied, actively fished basin — the Upper Paraná — without evidence of significant population decline or range restriction driving a threatened listing.
The Upper Paraná basin as a whole faces long-term pressure from damming, water-quality change and habitat modification associated with a heavily developed river system, and curimatids in general are of some importance to regional subsistence and small-scale fisheries; however, no source reviewed here ties a specific conservation concern to C. naegelii beyond its current Least Concern status.