Taxonomy & naming
Sternarchorhynchus schwassmanni was described by de Santana and Vari in 2010, in a major revision of the genus Sternarchorhynchus published in the Zoological Journal of the Linnean Society, which raised the genus from a handful of recognised species to more than thirty through detailed comparative and phylogenetic work. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes, a group of bony fish defined by a ribbon-like anal fin used for locomotion and by an electric organ used for sensing and signalling rather than by any resemblance to the unrelated Asian featherback and clown knifefishes (Chitala, Notopterus), which belong to an entirely different order.
The species name honours Horst O. Schwassmann, an American-based ichthyologist recognised for his contributions to understanding the biology of electric knifefishes. Within Apteronotidae, the genus Sternarchorhynchus is set apart by its long, gently downward-arched tubular snout, and it is by a wide margin the most species-rich genus in the family — more than two-thirds of its species are restricted to the Amazon basin, with the remainder, including S. schwassmanni, found in the Orinoco, the Golfo de Paria drainages, and a scatter of other basins such as the Essequibo, Maroni and Paraná. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for the valid name and type locality.
Morphology
Like other members of its genus, Sternarchorhynchus schwassmanni has the elongated, laterally compressed, blade-like body typical of Apteronotidae, extended at the front into a long, slender, tubular snout that gives the genus its common trade name of "tube-snouted" or "elephantnose" knifefish (a name it shares only in outline, not in relation, with the unrelated African elephantnose fishes of the genus Gnathonemus). As in all ghost knifefishes there is no dorsal fin and no true tail fin; movement is generated by undulations of a single long anal fin running along most of the underside, letting the fish glide forward or backward with equal control.
The electric organ, positioned along the body, and the sensory pores that read its self-generated field are diagnostic of the family. Apteronotidae are distinguished within Gymnotiformes by an electric organ built from modified nerve tissue rather than muscle, producing a fast, continuous wave-type discharge and giving the group the most refined electrolocation of any knifefish family. The skin is scaleless, as in all gymnotiforms. Specific size data for S. schwassmanni is data sparse, but relatives in the tube-snouted group of Sternarchorhynchus and related Apteronotidae reach up to roughly 19.5 in total length; this species should be assumed to fall in a comparable range pending confirmed measurements.
Habitat
Sternarchorhynchus schwassmanni is known from the Orinoco River system and from smaller rivers draining into the Golfo de Paria, on the border region of Venezuela and Trinidad — part of a broader distribution pattern in which this genus's non-Amazonian species cluster around the Orinoco and Golfo de Paria drainages, alongside smaller numbers in the Essequibo, Maroni and Paraná basins. As with its relatives, it is a fish of flowing Neotropical rivers rather than still water.
Apteronotidae in general favour slow-to-moderate river channels with dark, muddy or sandy substrates and dense cover from submerged vegetation, roots and leaf litter, and are active mainly at night. That nocturnal habit is inseparable from their electric sense: in turbid or tannin-stained water where vision is of limited use, a self-generated electric field is an effective way to navigate, avoid obstacles and locate prey. Detailed habitat data specific to S. schwassmanni beyond its basin-level distribution is data sparse.
Feeding
As a member of the tube-snouted Sternarchorhynchus group, S. schwassmanni is presumed to share the family's carnivorous, nocturnal foraging habits: hunting small invertebrates — worms, aquatic insect larvae and small crustaceans — hidden in sediment or among submerged roots, located largely through electrolocation rather than sight. The elongated snout characteristic of the genus is thought to aid in probing narrow spaces and substrate for such prey, though detailed dietary studies specific to this species are data sparse.
Because the species is essentially unknown in the aquarium trade, there is no hobbyist feeding record to draw on. What can be said with confidence, extrapolated from the family, is that any captive individual would need to be fed after dark on small meaty foods, in keeping with its nocturnal, electroreceptive hunting style.
Mating
No species-specific courtship or spawning observations for Sternarchorhynchus schwassmanni are documented in the available literature. What is well established for Apteronotidae generally, and studied in detail in laboratory-favoured relatives such as the brown ghost knifefish (Apteronotus leptorhynchus), is that the wave-type electric organ discharge carries information about a fish's species, sex and physiological state, and that during courtship males and females can shift their discharge frequencies toward one another in a kind of electrical duet, while rivals produce distinctive interruptions on encounter. It is reasonable to expect S. schwassmanni to use its electric discharge in a broadly similar way, given the shared electrosensory architecture of the family, but this has not been directly documented for the species.
Given how rarely Sternarchorhynchus species are encountered even by researchers, let alone observed spawning, this remains an area where the honest answer is that courtship and pairing behaviour are poorly known and not something to speculate about further.
Breeding
Breeding biology for Sternarchorhynchus schwassmanni is data sparse to the point of being effectively undocumented. As with most Apteronotidae outside the handful of species maintained for research (chiefly Apteronotus leptorhynchus and A. albifrons), there is no aquarium or field breeding record for this species. It can be inferred from the family that it is an egg-layer, likely spawning among cover such as roots or submerged vegetation, with no meaningful parental care afterward — but this is an inference from relatives, not a direct observation of S. schwassmanni.
This species has essentially no presence in the aquarium trade, so there is no captive-breeding history to describe. The honest summary is: egg-laying is assumed based on family-wide biology, and the reproductive details are unknown.
In the aquarium
Sternarchorhynchus schwassmanni is not a fish encountered in the aquarium hobby. It is a narrow-range, deep-channel South American species collected mainly by researchers rather than for the ornamental trade, and there is no established husbandry record to draw on. Aquarists occasionally encounter other, more accessible members of the tube-snouted Sternarchorhynchus group under trade names like "elephantnose knifefish," and the general care principles for those relatives — very large, mature, quiet aquaria with soft acidic-to-neutral water in the mid-20s °C, subdued lighting, secure hiding places such as wide tubes or driftwood caves, and scrupulous water quality given the species' scaleless skin and sensitivity to ammonia, nitrate and copper-based medications — would apply if this species were ever kept, but none of that is a claim about S. schwassmanni specifically.
Given the complete absence of trade or husbandry history, the responsible statement for this species is simply that it should not be expected in aquarium retail, and that any specimen encountered would demand the specialist, large-tank conditions typical of deep-river Apteronotidae rather than treatment as a typical community fish.
Conservation
Sternarchorhynchus schwassmanni has not been formally assessed by the IUCN Red List; like many species in this large, recently revised genus, it currently lacks a conservation status and would be best regarded as Data Deficient pending assessment. It is known only from the Orinoco and Golfo de Paria drainage complex, a distribution pattern that, in narrow-range Neotropical river endemics generally, carries some vulnerability to habitat disturbance, damming, pollution and deforestation within its home rivers — but no documented population trend or specific threat has been recorded for this species.
As with much of the genus, the most useful conservation statement is one of humility: S. schwassmanni was only described in 2010, is not targeted by the aquarium trade, and remains poorly surveyed. Its status is better described as unknown than as either secure or threatened.