Taxonomy & naming
Sternarchella calhamazon was formally described in 2013 by Lundberg, Cox Fernandes, Campos-da-Paz and Sullivan, in a paper that singled it out as, by their sampling, the most abundant apteronotid species in the Amazon's principal river channels — a striking statement for a fish that had gone unnamed for so long. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes, the New-World electric knifefishes. Like its relatives it is a bony fish but an unusual one: the Apteronotidae are set apart from other gymnotiforms by an electric organ built from modified nerve cells rather than muscle tissue, which is what allows them to generate the fastest, highest-frequency discharges in the order.
The genus Sternarchella sits within Apteronotidae alongside better-known genera such as Apteronotus (the black and brown ghost knifefishes of the aquarium trade) and the tube-snouted Sternarchorhynchus. Sternarchella calhamazon is one of several species in the genus distinguished mainly by fine anatomical detail — caudal peduncle shape, the size and shape of the electric organ, elongation of the hemal spines, and the arrangement of small intermuscular bones adjacent to the electric organ — differences invisible without dissection or careful comparison, which is likely part of why the species escaped formal recognition for so long. As with all valid names in the family, the Catalog of Fishes (Eschmeyer, CAS) is the taxonomic authority of record. These New-World gymnotiforms are not related to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance in body shape is convergent, not a sign of kinship.
Morphology
Sternarchella calhamazon is the smallest species in its genus, reaching a maximum recorded total length of about 6.5 in — modest even by ghost-knifefish standards, and far smaller than trade species like the black ghost. It follows the standard apteronotid body plan: a slim, laterally compressed, blade-like body with no dorsal fin and no true tail fin, propulsion coming instead from a long anal fin that runs along most of the underside and drives the fish forward or backward with equal facility. The skin is scaleless, like all gymnotiforms.
The electric organ running through the body is the feature that defines the genus and species-level distinctions within it — its size, shape and the bone structure around it are the primary characters separating S. calhamazon from its congeners. That organ produces an extraordinarily fast wave-type discharge, reported at roughly 772 to 2,180 Hz, among the fastest biological oscillations documented in any animal. Sensory pores over the skin read the resulting electric field, giving the fish a picture of its surroundings that substitutes for vision in the dark water it inhabits.
Habitat
The type locality is in the río Madeira in Pará, Brazil, roughly 22 mi above its confluence with the main Amazon, where the original specimens were collected from a deep channel some 14 to 16 metres down. That depth is characteristic: S. calhamazon is a fish of the Amazon's deep river channels rather than its floodplain lakes or marginal vegetation, and it is reported as widespread and abundant across deep channels throughout the wider Amazon basin.
Living at that depth, in fast-flowing, sediment-laden water far from the light, makes an electric sense essential rather than optional — vision is of little use tens of metres down in a turbid river, and electrolocation lets the fish navigate, find food and detect other fish regardless. This is a genuinely deep-water Amazonian species, and nothing in the available literature suggests it occurs outside that setting.
Feeding
Sternarchella calhamazon is documented as omnivorous, an unusual note within a family whose members are mostly regarded as small-prey carnivores. Stomach content studies found planktonic organisms alongside fish scales, sometimes in distinct stacks, suggesting the species picks up scales opportunistically rather than as its primary food. Its diet composition has been reported to track the availability of food resources in its deep-channel habitat rather than following one fixed prey type — a flexible, opportunistic feeding strategy suited to a demanding stretch of river.
As with other apteronotids, prey and food particles are almost certainly located using electrolocation as much as any other sense, given the depth and turbidity of the channels the species lives in. It has also turned up in broader trophic-ecology surveys of lowland Amazon fish assemblages, underscoring its place as a routine, if inconspicuous, part of the deep-channel food web rather than a specialist predator of any one prey type.
Mating
No courtship or spawning behaviour has been documented for Sternarchella calhamazon specifically; the species is known almost entirely from taxonomic and ecological survey work, not from observation of live fish over time. What can be said follows from its family. In apteronotids generally, the wave-type electric organ discharge doubles as a social signal as well as a sensing tool, carrying information about a fish's identity, sex and readiness to spawn — best studied in the related genus Apteronotus, where males and females shift discharge frequency during courtship in an electrical exchange. Given S. calhamazon's unusually fast discharge, it is reasonable to assume a comparable role for its EOD in signalling to conspecifics in the dark, deep channels it inhabits, though this has not been directly studied in the species.
Data is sparse on every other aspect of its reproductive behaviour, and nothing should be inferred beyond what the family's biology suggests.
Breeding
There is no documented breeding record for Sternarchella calhamazon, in the wild or in captivity — it is essentially unknown outside taxonomic and survey collections, and has no established presence in the aquarium trade to draw hobbyist observation from. As an apteronotid, it can be inferred to be an egg-layer that spawns among cover rather than a livebearer or mouthbrooder, with no meaningful parental care after spawning, matching the pattern documented in its better-known relatives. Beyond that inference, the honest position is that its reproductive biology is data sparse and unrecorded.
In the aquarium
Sternarchella calhamazon has no meaningful presence in the aquarium hobby. It is a deep-channel Amazon specialist, collected mainly for scientific survey and taxonomic work rather than the ornamental trade, and nothing in the available literature suggests it has ever been kept or bred in a home aquarium. Its natural habitat — flowing water 14 metres or more deep, in the Amazon's main channels — is also not something an aquarium can meaningfully replicate.
What can be said follows from its family and its biology rather than from hobbyist experience: like all gymnotiforms it is scaleless and would need careful, reduced-dose medication and clean, low-nitrate water if it were ever kept; like other apteronotids it would be most active in dim light and would need secure cover to feel safe. Anyone who does encounter this species — most likely as a wild-caught specimen mixed in with shipments of more common ghost knifefish — should treat it as a demanding, poorly understood fish rather than a casual purchase, and prioritise water quality and shelter over display.
Conservation
Sternarchella calhamazon has not been formally assessed by the IUCN Red List; its status is Not Evaluated. Nothing in the literature suggests it is a species of conservation concern — quite the opposite, the original description flags it as one of the most abundant apteronotids in the Amazon's principal channels, and it has since turned up widely across deep channels throughout the basin in survey work, indicating a broad range and healthy populations rather than a narrow-range endemic under pressure.
That said, an unassessed species is not the same as a confirmed-safe one, and deep-channel Amazon habitat is not immune to the basin-wide pressures facing the region — damming, sediment change, and pollution among them. Given the lack of a formal assessment or any documented population decline, the appropriate stance is simply to note the gap rather than assign a status the data does not support.