Taxonomy & naming
Sternarchorhynchus roseni was described by Francisco Mago-Leccia in 1994 and 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 Gymnotiformes are defined by an electric organ and a single long ribbon-like anal fin used for propulsion, and the Apteronotidae are set apart within the order by an electric organ derived from modified nerve tissue rather than muscle, giving them the fastest, highest-frequency discharges of any knifefish group.
The genus Sternarchorhynchus is the most species-rich genus within Apteronotidae, and S. roseni has been placed by researchers within the informal "Sternarchorhynchus curvirostris group" on the basis of anal- and pectoral-fin coloration. Despite sharing the common name "knifefish", these South American fish are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance in body shape is convergent, not a sign of kinship. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for the valid name.
Morphology
As in other members of its genus, Sternarchorhynchus roseni has the elongated, tube-snouted head typical of the group, a slender laterally compressed body, and no dorsal or true tail fin — propulsion instead comes from a long anal fin rippling in travelling waves that lets the fish move forward or backward with equal ease. The known reference specimen, a female held at the Los Angeles County Museum (LACM 43252-3), measured 15 in in total length, the largest size documented for the species. The genus is generally described as monochromatic dark brown, and the fish is scaleless like all gymnotiforms.
Running the length of the body is the electric organ, paired with sensory pores across the skin that read the field it produces. Males of Sternarchorhynchus species are reported to develop external teeth during the breeding season, a feature tied to territorial and reproductive behavior rather than to feeding. The species has also been noted, at genus level, to be capable of regenerating a lost tail.
Habitat
Sternarchorhynchus roseni is known from the Orinoco basin of Venezuela, with its type locality in the Río Apure at Jarina, near San Fernando de Apure — placing it, on current evidence, as a narrow-range endemic of the Río Apure system rather than a species with a broad Orinoco-wide distribution. As with other tube-snouted ghost knifefishes, it is presumed to inhabit river channels and margins, likely among submerged roots, sand and leaf litter, though detailed field observations specific to this species are not documented in available sources.
Genus-level accounts describe Sternarchorhynchus species as primarily crepuscular, emerging to feed as light fades, in warm, soft to moderately mineralised, near-neutral river water. That dim, often turbid or tannin-stained environment is where the electric sense does its work: where vision is of limited use, an electric field lets the fish navigate, avoid obstacles, and detect prey and rivals by the way they distort it.
Feeding
Sternarchorhynchus roseni is presumed, on the strength of its tube snout and its placement within a genus built around this feeding mode, to be a specialised predator of small invertebrates probed out of sediment, root tangles and crevices — a "grasp-suction" style of prey capture has been described for the Sternarchorhynchus curvirostris group to which this species has been assigned, using the elongated snout to reach into confined spaces before drawing prey in.
Related congeners in the genus are reported to accept frozen and live foods such as tubifex and bloodworms readily in captivity, feeding mostly after dusk when they become active. No aquarium-specific feeding record exists for S. roseni itself; this account reflects genus-level behavior and should be read as inference rather than direct observation of the species.
Mating
As in other Apteronotidae, courtship in Sternarchorhynchus is thought to be mediated substantially by the wave-type electric organ discharge, which in the family carries information about a fish's identity, sex and social status and in well-studied relatives shifts frequency during social and courtship encounters — an electrical exchange running alongside physical approach in the dark. Male Sternarchorhynchus developing external teeth during the breeding season points to territorial, competitive behavior around spawning, and the genus has been described as territorial and rather aggressive.
No courtship behavior specific to Sternarchorhynchus roseni has been documented in the sources available for this account. What can be said with confidence is drawn from electrophysiology and genus-level natural history rather than from direct observation of this species spawning.
Breeding
Breeding biology for Sternarchorhynchus roseni is essentially undocumented — it is not a species reported in the aquarium trade, let alone bred there, and no scientific account of its spawning has turned up in available sources. Like other Apteronotidae it is presumed to be an egg-layer with no substantial parental care, based on what is known for the family generally, but this is inference rather than a confirmed record for the species.
Data sparse: rather than construct a breeding protocol that has no basis in the literature, this account notes plainly that reproduction in the wild, and any prospect of captive breeding, remains unknown for this narrow-range Orinoco endemic.
In the aquarium
Sternarchorhynchus roseni is not an established aquarium fish; it does not appear to be part of the ornamental trade, and the notes here draw on genus-level care information for related Sternarchorhynchus species rather than on any record specific to S. roseni. Congeners in the genus have been kept in large aquaria (minimum around 150 US gal), pH roughly 6.5–7.0, temperatures 73–82 °F with 79 °F cited as optimal, well-oxygenated and gently flowing, with subdued lighting and secure hiding places such as pipes or root tangles — conditions consistent with its dim, crepuscular native habitat.
As with all gymnotiforms, any specimen kept would need particular care around water quality and medication: being scaleless, these fish are sensitive to ammonia and nitrate, and to copper-based and other harsh treatments, which should be dosed at reduced strength. Genus relatives are described as peaceful toward small tankmates and easily fed on frozen and live foods once settled. Given the total absence of a trade or husbandry record for this specific species, any aquarist encountering it should treat it as a specialist proposition requiring mature, stable, well-oxygenated water rather than a beginner's fish.
Conservation
Sternarchorhynchus roseni is assessed on the IUCN Red List as Least Concern. It is known from the Río Apure system within the Orinoco basin of Venezuela, and on current evidence appears to be a narrow-range, single-river-system endemic, though no population trend, harvest pressure or specific threat has been documented that would argue against the listing.
No specific conservation program has been documented for this species in available sources. Given the narrow known range on record, this Least Concern listing should be understood as reflecting an absence of documented decline rather than a dense body of dedicated population study.