Taxonomy & naming
Sternarchorhynchus stewarti was described by de Santana & Vari in 2010 as part of a sweeping revision of the genus Sternarchorhynchus, published in the Zoological Journal of the Linnean Society. That single paper described 22 new species and raised the genus total to 32, reflecting how poorly sampled these deep-channel Amazonian electric fishes had been until recently. S. stewarti was placed directly in Sternarchorhynchus with no earlier combination to its name.
The genus belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. These are bony fish, but unusual ones: Gymnotiformes are set apart by an electric organ and a single long anal fin used for locomotion, and the Apteronotidae in particular carry an electric organ built from modified nerve cells rather than muscle, giving them the fastest, highest-frequency discharges in the order. Despite the shared common name, gymnotiform knifefishes are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance is convergent, not a matter of kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
Sternarchorhynchus is the tube-snouted genus within the ghost knifefishes, named for the elongated, downward-tapering snout that gives the group its rhynchus ("snout") epithet — an adaptation for probing into sediment and crevices. Like its relatives, S. stewarti has a blade-like, laterally compressed body, no dorsal fin, and no true tail fin; propulsion comes from a single long anal fin thrown into travelling waves, letting the fish move forward or backward with equal ease. It is scaleless, as all Apteronotidae are.
FishBase records a maximum total length of 9 in for S. stewarti, a modest size for the family. Running the length of the body is the electric organ, and the skin carries the sensory pores that read the field it produces — in Sternarchorhynchus this is a fast, tone-like wave-type discharge, reported for the genus in the roughly 944–1992 Hz range, among the highest frequencies known in the order. Detailed data on sexual dimorphism have not been published for this species.
Habitat
Sternarchorhynchus stewarti is known from South America, from rivers of southeastern Peru and eastern Ecuador, placing it in the western headwater reaches of the Amazon and Orinoco drainages. It is a freshwater, benthopelagic fish of tropical rivers, living and foraging near the bottom of flowing channels rather than in still water.
No species-specific temperature or pH data have been published, but the pattern across Apteronotidae is consistent: warm (roughly 23–28 degrees Celsius), soft to moderately mineralised, near-neutral to acidic river water, often turbid or tannin-stained. That darkness suits an animal that navigates primarily by electrolocation rather than sight — conditions where eyes are of limited use and an electric field is the more reliable sense.
Feeding
No dedicated feeding study has been published for Sternarchorhynchus stewarti, and its diet is data sparse. Its elongated, tube-like snout is characteristic of substrate-probing feeding, and related ghost knifefishes with similar snout shapes are understood to hunt small benthic invertebrates — aquatic insect larvae, worms and small crustaceans — buried in sediment or tucked among roots, located largely through electroreception rather than sight.
As in other Apteronotidae, feeding activity in the wild is expected to be concentrated after dark, when the fish's electric sense gives it an advantage over sighted predators and prey alike. Nothing further can be stated with confidence without over-reaching the source material.
Mating
Courtship biology has not been documented for Sternarchorhynchus stewarti specifically, but the broader pattern in Apteronotidae is well established through electrophysiology, chiefly in the brown ghost knifefish (Apteronotus leptorhynchus). In that species, the wave-type electric organ discharge carries information about identity, sex and reproductive readiness, and males and females shift their discharge frequencies during courtship in a kind of electrical duet; rival fish produce distinctive interruptions when they meet. Given that S. stewarti shares the same wave-type discharge system, its courtship very likely involves comparable electric signalling, though this has not been directly studied in the species.
Beyond that inference, nothing is published on pairing behaviour, spawning sites, or timing for this species. It should be treated as data sparse rather than assumed to match any particular protocol.
Breeding
Sternarchorhynchus stewarti is not a species with any documented aquarium or captive breeding history; it is essentially unknown in the trade. Like other Apteronotidae, it is presumed to be an egg-layer, but the mode of reproduction, spawning triggers, and any parental care have not been described for this species and should be considered poorly documented.
Across the family, where breeding has been observed at all it has tended to involve mature fish scattering eggs among cover such as roots or crevices, with no substantial parental care afterward. For S. stewarti there is no basis to go beyond that general family pattern — the honest position is that its breeding biology is effectively unrecorded.
In the aquarium
Sternarchorhynchus stewarti is not an aquarium fish in any meaningful sense; it belongs to a large group of deep-channel Amazonian Apteronotidae that are rarely if ever collected for the trade, in contrast to the familiar black ghost (Apteronotus albifrons) or brown ghost (A. leptorhynchus). Any care guidance has to be extrapolated from the family rather than from direct experience with this species.
Were it ever kept, the general Apteronotidae rules would apply: it is scaleless and would need great care with medications, avoiding copper-based treatments and reducing standard doses, along with sensitivity to ammonia and nitrate that calls for mature filtration and clean, warm, soft, gently-moving water. As a presumed nocturnal, electrolocating predator with a probing snout suited to picking invertebrates out of sediment, it would need dim lighting, secure cover, and tankmates too large to be treated as prey. None of this has been tested for S. stewarti specifically, and it should not be treated as an aquarium candidate on the strength of this entry.
Conservation
Sternarchorhynchus stewarti is assessed as Least Concern on the IUCN Red List. No detailed threat assessment or population trend has been published in the material reviewed here.
As with many narrow-range Amazonian and Orinoco headwater fishes, the general pressures facing the region — deforestation, mining-related sediment and mercury pollution, and river modification — are the ones most likely to matter to species like this over time, even where a Least Concern rating currently applies. Given how recently S. stewarti was described (2010) and how little has been published on it since, its true status is better understood as an open question than a settled one.