Taxonomy & naming
Sternarchorhynchus hagedornae was described by de Santana & Vari in 2010 and placed in 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 set apart by an electric organ and a long ribbon-like anal fin used for propulsion in place of a normal tail. Within the order, the Apteronotidae are distinguished by an electric organ built from modified nerve cells rather than muscle, giving them the fastest, highest-frequency discharges of any knifefish family.
The genus Sternarchorhynchus is recognisable by its long, tubular, downturned snout, used to probe for food rather than to bite. Despite the shared common name, these New-World knifefishes are not related to the Asian featherback or clown knifefishes (Chitala, Notopterus); the resemblance in body shape is convergent, not a sign of kinship. The species epithet honours Mary Hagedorn, a marine biologist at the Smithsonian Institution. The Catalog of Fishes is the authority for the valid name.
Morphology
Sternarchorhynchus hagedornae is a small, laterally compressed knifefish with the elongated, tubular snout characteristic of its genus, used to probe crevices and sediment for prey rather than for direct sensing at the tip. As in other Apteronotidae, there is no dorsal fin and no distinct tail 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 ease. The species is scaleless, like all gymnotiforms.
Size differs between the sexes: males reach a maximum of about 10 in total length and females about 8 in, a modest difference reported directly from type and voucher material rather than from aquarium observation. An electric organ runs along the body beneath the skin, paired with sensory pores that read the electric field it produces — the sensory system this fish relies on far more than vision in the fast, often turbid water it inhabits.
Habitat
The species is known from the Quebrada Pachija, part of the Río Manu basin in Peru, an Amazonian tributary system. Its recorded habitat is an open-gallery, high-flow stream with rocky rapids — swifter, more oxygenated water than the sluggish backwaters and floodplain channels favoured by many other gymnotiforms.
As with other Apteronotidae, its electric sense is best understood as a substitute for vision in water where sight is of limited use, whether because of turbidity, shade from gallery-forest cover, or nocturnal activity. Occurrence records from the Amazon basin in Peru are consistent with a distribution centred on the Manu drainage rather than a wide, continent-spanning range.
Feeding
Sternarchorhynchus species forage for aquatic insect larvae and small burrowing invertebrates, probing sediment, gravel and crevices in swift water with the long tubular snout. The snout shape suggests a specialised, close-range foraging style — worked into tight spaces among rocks and debris rather than open pursuit of prey in the water column.
As in other ghost knifefishes, electrolocation almost certainly plays a central role in finding buried or hidden prey in fast, often dim water, though the cache does not document a study specific to this species' feeding behaviour. Nothing is documented in the available sources about diet or feeding in aquarium conditions; this is a data-sparse area for the species.
Mating
No species-specific account of courtship in Sternarchorhynchus hagedornae is documented in the available sources. As in other Apteronotidae, the electric organ discharge is understood across the family to serve as more than a sensing tool — a wave-type signal that can carry information about a fish's identity, sex and condition, with courtship in well-studied relatives such as the brown ghost knifefish involving shifts in discharge frequency between paired fish. Whether this pattern holds for S. hagedornae specifically has not been documented.
Given how little is recorded of this species beyond taxonomy and distribution, any detail of mating behaviour beyond the general electric-signalling pattern shared across the family would be speculation; the honest position is that this is unstudied.
Breeding
Breeding biology for Sternarchorhynchus hagedornae is not documented in the available sources. Across the Apteronotidae generally, reproduction is by egg-laying, spawning is thought to occur among cover such as roots and crevices, and no substantial parental care has been described for the family's better-known species. Whether this species has ever been bred in captivity is unrecorded — it is not established in the aquarium trade, and no husbandry or spawning account exists to draw on.
The fair summary for this species is rarely studied, poorly documented, and, as far as available sources show, not bred in aquaria.
In the aquarium
Sternarchorhynchus hagedornae is not an aquarium fish in any meaningful sense — it does not appear to be part of the ornamental trade, and no husbandry information is documented in the available sources. Like other scaleless gymnotiforms it would be expected to share the family's general sensitivities: vulnerability to ammonia and nitrate, and a need for reduced doses of copper-based or other harsh medications, should it ever be kept.
Given its narrow known range in a fast-flowing, rocky Amazonian stream, any speculative care would call for well-oxygenated, flowing, dimly lit water — but this is inference from its habitat and its family, not documented husbandry, and the species should be treated as effectively unavailable and unstudied in captivity.
Conservation
Sternarchorhynchus hagedornae is assessed by the IUCN as Least Concern. It is known from the Río Manu basin in Peru, an area that includes significant protected forest, which may help buffer the localized habitat it depends on from some of the pressures — deforestation, mining, and water-quality decline — that threaten other Amazonian streams.
As with many narrow-range Apteronotidae, its status reflects limited assessed threat rather than abundant data on population trends; single-basin endemics like this one remain more exposed to local habitat disturbance than their Least Concern listing might suggest on its own.