Taxonomy & naming
Sternarchorhynchus higuchii 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 the rest of the order 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 fins and scales that mark most freshwater aquarium fish. The Apteronotidae are set apart within Gymnotiformes by a neurogenic electric organ, built from modified nerve cells rather than muscle, which produces the fastest and most stable wave-type discharges of any knifefish family.
The genus Sternarchorhynchus is the "tube-snouted" lineage of ghost knifefish, named for an elongated, tubular snout quite different from the blunter head of the familiar black ghost. The species epithet honours Horácio Higuchi of the Museu Paraense Emílio Goeldi. As with all gymnotiforms, these New-World fish are unrelated to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus); the shared "knifefish" name reflects convergent body shape, not kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
Sternarchorhynchus higuchii reaches a recorded maximum of about 9.5 in total length, modest even by the standards of the tube-snouted ghost knifefishes. As in other members of the genus, the head is drawn out into a slender, elongated snout, and the body is scaleless, laterally compressed and blade-like, tapering to a whip-thin tail with no distinct caudal fin and no dorsal fin at all. Locomotion comes from a long anal fin running beneath most of the body, thrown into travelling waves that let the fish move forward or backward with equal control — useful in the tight spaces of the debris and root tangles these fish favour.
The electric organ runs the length of the body beneath the skin, paired with an array of electroreceptor pores, and produces a wave-type discharge — a near-continuous, high-frequency signal characteristic of the family, generated by nerve tissue rather than muscle. Beyond the type description and the diagnostic length and snout proportions used to distinguish it from congeners, detailed morphological data for this species is sparse.
Habitat
Sternarchorhynchus higuchii is known from tropical South America, recorded from Brazil, and is treated by the IUCN as a putative narrow-range endemic — a fish restricted to a limited stretch of habitat rather than broadly distributed across the Amazon basin. Like other Sternarchorhynchus it is a benthopelagic, freshwater species associated with the deeper channels of Amazonian rivers, a habitat niche shared across the tube-snouted ghost knifefishes.
As with its relatives, this is warm, typically soft and often turbid or tannin-stained water, where visibility is poor and an electric sense does the work that eyes cannot. Fine-grained habitat detail — depth, substrate, current, associated vegetation — has not been published for this particular species beyond its general placement in deep river channels; much of what can be said follows from the pattern shown by better-studied congeners rather than direct observation of S. higuchii itself.
Feeding
No species-specific dietary study has been published for Sternarchorhynchus higuchii. Ghost knifefishes in general are nocturnal carnivores that hunt small invertebrates — aquatic insect larvae, worms and small crustaceans — using electrolocation to detect prey hidden in sediment or tucked among roots and debris in the dark. The elongated, tubular snout typical of Sternarchorhynchus is consistent with probing into narrow crevices and substrate for buried prey, a common feeding style among tube-snouted gymnotiforms, though this remains an inference from the genus rather than a documented observation of this species.
Because it is essentially unknown in the aquarium trade, there is no hobbyist feeding record to draw on either. Data sparse.
Mating
Nothing specific has been published on courtship or spawning behaviour in Sternarchorhynchus higuchii. Across the ghost knifefishes generally, the wave-type electric organ discharge is understood to carry information beyond simple electrolocation — signalling identity, sex and reproductive state to other fish, with courtship in well-studied relatives such as Apteronotus involving shifts in discharge frequency during encounters between males and females. It is reasonable to expect a broadly similar role for electric signalling in this species, but that has not been demonstrated for S. higuchii itself, and the point should be read as inference from the family rather than a documented fact.
Breeding
Breeding biology in Sternarchorhynchus higuchii is essentially undocumented. Gymnotiforms in general are egg-layers, and where breeding has been observed in related ghost knifefishes it involves eggs scattered among cover such as roots or crevices, with no substantial parental care afterward. This species has not been recorded breeding in captivity — it is not established in the aquarium trade at all — and no protocol or spawning account exists in the literature reviewed here. Data sparse; parental care is not documented for this species.
In the aquarium
Sternarchorhynchus higuchii is not a fish of the aquarium hobby. The tube-snouted Sternarchorhynchus species are deep-channel Amazonian fish rarely if ever seen in the trade, and this species in particular — narrow-ranged and assessed as Critically Endangered — should not be sought as an aquarium subject. The general husbandry lessons that apply to its better-known relatives (a scaleless fish sensitive to copper-based medications and to ammonia and nitrate, needing dim, cover-rich, warm and gently flowing water, and active mainly after dark) would presumably apply if it were ever kept, but there is no documented aquarium care history for this species to draw on. Any specimen encountered would be far better served by conservation attention than by collection.
Conservation
Sternarchorhynchus higuchii is assessed as Critically Endangered on the IUCN Red List, under criteria B2ab(ii,iii,v), in an assessment dated 7 November 2018. The IUCN notes it as a putatively narrow-range endemic restricted to a limited area of Brazil, the kind of single-basin specialist that is disproportionately exposed to localized habitat change, water quality decline and other river pressures even when the wider Amazon basin remains extensive.
As with many gymnotiforms, the species is not tracked in the aquarium trade and faces no meaningful collection pressure from the hobby; its conservation concern stems from habitat rather than exploitation. Given how little natural-history data exists for the species beyond its original description and Red List assessment, further field survey work would be needed to clarify the precise threats and population trend behind its Critically Endangered status.