Taxonomy & naming
Sternarchorhynchus britskii was described by Ricardo Campos-da-Paz in 2000, in a revisionary paper on the genus Sternarchorhynchus that also described a second new species; the type locality is the upper Rio Paraná, Brazil. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: they are defined by an electric organ run the length of the body and by a single long anal fin used for locomotion in place of a normal tail and dorsal fin.
Within Apteronotidae, the family is set apart by a neurogenic electric organ — derived from modified nerve cells rather than muscle — that produces the fastest, most refined wave-type discharges of any electric fish. Sternarchorhynchus is one of the most species-rich genera in that family, and S. britskii is placed in the S. curvirostris species-group alongside S. curvirostris and S. roseni, distinguished from relatives chiefly by anal- and pectoral-fin colour pattern and fin-ray counts. These New-World knifefishes 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 is the authority for the valid name.
Morphology
Sternarchorhynchus britskii has the elongated, laterally compressed body typical of the genus, with a greatest body depth around 6.9–7.9 times the total length and a head length roughly 4.7–5.2 times the total length — a slim, blade-like fish rather than a deep-bodied one. The mouth is terminal at the end of a distinctively elongated, tubular snout, the feature that gives the genus its common informal name of "tube-snouted knifefish"; the snout and jaws are structurally modified for a grasp-and-suction feeding action on small prey worked out of the substrate.
Fin-ray counts are diagnostic within the genus: the anal fin — the fish's sole means of propulsion, rippled in travelling waves to move it forwards or backwards with equal ease — carries 166–178 soft rays, the pectoral fins 14–15 rays, and there are 80–90 vertebrae and 11–13 transverse scale rows above the lateral line. As in other Apteronotidae there is no dorsal fin and no separate tail fin. The species is scaleless over most of the body, and reaches a recorded maximum of about 10 in total length. Running beneath the skin along the body is the electric organ, paired with sensory pores that read the field it produces.
Habitat
The species is known from the Paraná River basin of South America, a large freshwater system draining parts of Brazil, Paraguay and Argentina. FishBase describes it as a benthopelagic fish of tropical freshwater, consistent with the genus's general habit of living in deeper river channels — often five metres or more down — where little or no light penetrates.
Detailed habitat data for this particular species is sparse, but the wider Apteronotidae to which it belongs are found through the humid Neotropics from Panama to northern Argentina, almost always in flowing water rather than still swamp, and typically in warm, dim conditions where a refined electric sense — rather than eyesight — does the work of finding prey and avoiding obstacles.
Feeding
FishBase places Sternarchorhynchus britskii at a trophic level of about 3.3, consistent with a diet of invertebrates and small fish rather than detritus or plant matter. The elongated, tubular snout and the modified jaw and suspensorium described in the genus's revisionary literature point to a specialised feeding method: probing into soft sediment, root tangles or leaf litter to grasp and suck up small buried prey, likely aquatic insect larvae and other benthic invertebrates, in the manner typical of tube-snouted Sternarchorhynchus species.
As in other Apteronotidae, feeding is almost certainly nocturnal and guided chiefly by electrolocation: the fish's weak electric field is distorted by anything nearby with different conductivity than the surrounding water, letting it detect prey hidden from sight in dark, turbid river channels. Specific dietary items for S. britskii have not been documented in the available literature; this account should be read as inference from the genus rather than direct observation of this species.
Mating
No courtship or spawning behaviour has been documented for Sternarchorhynchus britskii specifically. What is known comes from the biology of Apteronotidae generally: the wave-type electric organ discharge is not just a sensing tool but a social signal, encoding a fish's identity, sex and reproductive state, and in well-studied relatives such as the brown ghost knifefish (Apteronotus leptorhynchus) males and females shift their discharge frequencies during encounters in a kind of electrical duet. It is reasonable to expect similar electric signalling plays a role in this species' courtship, but that has not been confirmed by direct study.
FishBase records no maturity or spawning data for S. britskii, and the species' deep-channel, largely inaccessible habitat means courtship in the wild has essentially never been observed by researchers. This account is deliberately conservative rather than speculative on this point.
Breeding
Breeding biology for Sternarchorhynchus britskii is essentially undocumented — data sparse. The species is not established in the aquarium trade, has no aquarium-breeding record, and FishBase lists no reproductive guild or maturity data. Based on the wider family, it is presumed to be an egg-layer, as all Apteronotidae are, but the location, timing and any parental involvement in spawning are unknown for this species.
Given how rarely even the popular, widely traded ghost knifefishes (such as the black ghost) are bred in captivity, and that S. britskii is essentially never seen in the hobby, there is no realistic prospect of aquarium breeding data emerging soon. Prefer this honest gap over any invented protocol.
In the aquarium
Sternarchorhynchus britskii is not a hobby fish. It does not appear in the aquarium trade, has no husbandry record, and — like other deep-channel Sternarchorhynchus species — would be a poor candidate for captivity even if it were available: it is adapted to deep, dark river channels and its tube-snout feeding apparatus is highly specialised for probing sediment for buried prey, not for accepting typical aquarium foods.
What can be said generally, extrapolated from its Apteronotidae relatives, is that any electric knifefish of this kind would need warm, soft, near-neutral to acidic water, dim lighting and secure cover, plus real caution with medications: like other Gymnotiformes it is scaleless, which in related species brings sensitivity to ammonia, nitrate, and copper-based or harsh treatments. This is offered as background biology, not as a stocking recommendation — this is a museum-and-literature species, not an aquarium one.
Conservation
Sternarchorhynchus britskii is assessed by the IUCN Red List as Data Deficient, reflecting how little is known of its population size, trend or the extent of threats it faces; the assessment was last updated in May 2022. This status is typical for the genus, most of whose ~35 described species are known only from limited museum collections in deep, poorly surveyed river channels across the Neotropics.
Its range within the Paraná River basin means it is potentially exposed to the pressures common across that heavily dammed and developed system — altered flow regimes, water-quality decline and habitat modification — but no species-specific population data exists to confirm an effect. Given the Data Deficient status, no elevated conservation concern is claimed here beyond what the assessment itself states.