Taxonomy & naming
Sternarchorhynchus oxyrhynchus was described by Müller & Troschel in 1849 and belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Like all Gymnotiformes it is a bony fish but an unusual one, defined by an electric organ and a long ribbon-like anal fin rather than by the fin arrangement of typical aquarium fish. Apteronotidae are distinguished within the order by a neurogenic electric organ, built from modified nerve-cell axons rather than muscle, which produces the fastest and most refined wave-type discharges of any knifefish family.
The genus Sternarchorhynchus is a large, taxonomically active group of tube-snouted Apteronotidae found across Amazonian and Orinoco river systems; phylogenetic and revisionary work on the genus has continued to clarify species boundaries. The common name "knifefish" is shared with the unrelated Asian featherback and clown knifefishes (Chitala, Notopterus), which belong to a different order entirely — the resemblance is convergent, not a sign of kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
The most obvious feature of Sternarchorhynchus oxyrhynchus is its snout: elongated and tubular, projecting well forward of the mouth, which gives the fish its elephant-nose trade name. The body is elongate and laterally compressed in typical ghost-knifefish fashion, tapering to a thin tail, with no dorsal fin and no distinct caudal fin; locomotion comes from a long anal fin run as a travelling wave along the underside of the body, letting the fish move forward or backward with equal control. Reported maximum size is around 18.5 in total length, with some trade sources citing fish up to about 19.5 in.
As in other Apteronotidae, the electric organ runs the length of the body and the skin is dotted with electroreceptor pores that read the field it produces. The species is scaleless, a trait shared across the family that makes the skin sensitive to poor water quality and to certain medications. Detailed data on sexual differences in body form are not documented for this species; in related Apteronotidae, sexes are difficult to distinguish externally and are more reliably told apart by electric-organ-discharge frequency than by shape.
Habitat
Sternarchorhynchus oxyrhynchus is native to northern South America, recorded from Venezuela, the Guianas and the Brazilian Amazon. FishBase and GBIF occurrence records place it as a benthopelagic freshwater fish of slow-moving tropical rivers, streams and their tributaries, generally over soft mud or sand substrates rather than gravel or rock.
Waters in this range are warm and typically soft to moderately hard, with a near-neutral to slightly acidic pH, and often turbid or tannin-stained — conditions in which eyesight is of limited use and an electric sense becomes the primary way to read the environment. The species is understood to be nocturnal, resting by day and becoming active after dark, in keeping with the general pattern of Apteronotidae. Beyond these broad strokes, detailed habitat and behavioural data for this particular species are sparse.
Feeding
Diet in the wild is not well documented for Sternarchorhynchus oxyrhynchus specifically; FishBase notes its natural feeding ecology as largely unknown, though its elongated snout and benthic habits point to it probing sediment and crevices for small invertebrates in the manner typical of tube-snouted Apteronotidae, likely locating prey by electrolocation in the dark rather than by sight.
In the aquarium the species is reported as carnivorous, favouring live and frozen tubifex worms as a preferred food, and accepting bloodworm, chopped earthworm, brine shrimp and blackworm; newly acquired fish are generally weaned onto frozen foods over time. As with other nocturnal knifefish, feeding is best offered after lights-out, when the fish becomes active and forages over the substrate.
Mating
As in other Apteronotidae, the electric organ discharge in Sternarchorhynchus is understood to carry more than navigational information — it is a wave-type signal capable of encoding species identity, sex and social context, and in the well-studied congener Apteronotus leptorhynchus males and females are known to modulate discharge frequency during courtship and rival encounters. It is reasonable to expect a broadly similar role for electric signalling in courtship across the family, including this genus, though this has not been specifically documented in Sternarchorhynchus oxyrhynchus.
Beyond that family-level pattern, specific courtship behaviour for this species — how individuals locate and approach one another, or what physical displays if any accompany the electric signalling — is not documented in available sources. Data sparse.
Breeding
There is no documented account of Sternarchorhynchus oxyrhynchus being bred in captivity; one hobby source states plainly that no successful aquarium spawning has been reported. Like most Apteronotidae in the trade, individuals available to aquarists are believed to be wild-caught rather than captive-produced.
As an egg-laying gymnotiform it can be assumed, by analogy with better-studied relatives, to scatter eggs among cover such as roots or sediment with no substantial parental care, but this has not been confirmed for the species itself. The honest position for the aquarist is that breeding biology here is essentially unknown; nothing should be inferred beyond the general egg-laying pattern of the family.
In the aquarium
Sternarchorhynchus oxyrhynchus is considered a fish for moderate to advanced keepers. Sources recommend a minimum of roughly 55 US gallons (about 55 US gal) with efficient filtration, a soft sand or mud substrate rather than gravel, and low or minimal lighting to suit its nocturnal habits; hiding spots such as driftwood, rockwork or dense planting give it the security to rest through the day. Water is best kept warm, in the range of about 73–82 °F, with a near-neutral to slightly acidic pH and moderate hardness.
Being scaleless, it shares the family's sensitivity to salt and to harsh medications, and stable, well-filtered water is important to its health. It is generally described as peaceful toward other species but territorial and sometimes aggressive toward its own kind, so conspecifics need adequate space or should be kept singly in smaller setups. Reported lifespan in the trade runs from roughly 8 to 15 years across sources. As with all deep-snouted Apteronotidae, feeding requires attention: offer meaty foods after dark and watch that a long-snouted fish is actually getting food into its narrow mouth rather than losing it to faster tankmates.
Conservation
Sternarchorhynchus oxyrhynchus is assessed by the IUCN as Least Concern, last evaluated in 2020, reflecting a range that spans Venezuela, the Guianas and the Brazilian Amazon rather than a narrow single-river endemism. It is not currently considered a species of conservation concern.
As with other wide-ranging Amazonian gymnotiforms, the main long-term pressures across its range are habitat degradation from deforestation, damming and pollution rather than any threat specific to this species. Because aquarium specimens appear to be wild-collected rather than farmed, keeping demand modest and favouring reputable suppliers is a reasonable precaution even though the species is not currently at risk.