Taxonomy & naming
Sternarchorhynchus inpai was described by de Santana and Vari in 2010 as one of twenty-two new species erected in a single revisionary study of the genus Sternarchorhynchus, which brought the genus to thirty-two recognized species. It belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Like all gymnotiforms it is a bony fish, but an unusual one: the order is defined by its electric organs and by a long ribbon-like anal fin used for propulsion instead of a normal tail. Within Apteronotidae the electric organ is built from modified nerve cells rather than muscle, giving these fish an especially fast, high-frequency wave-type electric organ discharge that they use for electrolocation — sensing prey, obstacles and other fish in dark or turbid water — and for communication with each other.
The species epithet inpai honours INPA, the Instituto Nacional de Pesquisas da Amazônia in Manaus, reflecting the institution's role in Amazonian ichthyological research. Despite the shared common name "knifefish", Sternarchorhynchus and the other Gymnotiformes are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus), which belong to an entirely different order of bonytongues; the similar blade-bodied shape is convergent, not a sign of kinship. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Sternarchorhynchus species are recognisable within the ghost knifefishes by their elongated, tubular snout, a feature shared across the genus and reflected in the common English term "tube-snout knifefish" used for its relatives. The body is blade-like and strongly compressed from side to side in typical apteronotid fashion, with no dorsal fin and no conventional caudal fin; locomotion comes from a long anal fin run in travelling waves along the underside of the body, letting the fish move forward or backward with equal control. FishBase records a maximum length of 8.5 in total length for this species, modest compared with the black ghost knifefish but consistent with other members of the genus.
As in other Apteronotidae, the skin is scaleless, and the body carries the electric organ along its length together with the sensory pores that detect the field it produces. Detailed information on external sexual differences is not documented for this species; visible dimorphism has not been established in the sources available.
Habitat
Sternarchorhynchus inpai is known from Brazil, within the Amazon basin, and its original description places it among the many narrow-range species uncovered by the 2010 revision of the genus. It is a benthopelagic fish, living and foraging near the bottom of the water column rather than at the surface, in the kind of dark, turbid, sediment-rich river habitat typical of Amazonian channels — conditions in which vision is of limited use and an electric sense becomes the primary way of reading the environment.
Data on the precise river systems, depths and microhabitats occupied by this species are sparse beyond the basin-level record from FishBase; as with many of the Sternarchorhynchus species described in the same 2010 paper, detailed field ecology has not been widely published.
Feeding
FishBase records a trophic level of about 3.3, placing Sternarchorhynchus inpai as a carnivore, consistent with the feeding ecology of ghost knifefishes generally, which hunt small invertebrates and other prey in the sediment and among cover by night using electrolocation to detect the faint electrical signatures of buried or hidden animals. Specific dietary items and foraging behaviour have not been documented for this species individually; data are sparse beyond its broad trophic classification.
Mating
As in other Apteronotidae, the wave-type electric organ discharge in Sternarchorhynchus is understood to carry information beyond simple electrolocation — signalling identity, sex and readiness to spawn to other fish sharing the same water, a phenomenon best studied in relatives such as the brown ghost knifefish, where males and females shift discharge frequency in a courtship duet. Whether Sternarchorhynchus inpai shows comparable electric courtship behaviour has not been documented; it is inferred from the shared physiology of the family rather than direct observation of this species.
No species-specific account of courtship or spawning behaviour for S. inpai exists in the available literature. Data are sparse.
Breeding
Sternarchorhynchus inpai is not known to have been bred in captivity, and it has no established presence in the aquarium trade. Like other Apteronotidae, the genus is presumed to be egg-laying, but there is no documented account of spawning behaviour, egg placement or parental care for this species. As with most of the genus, breeding remains entirely undescribed outside the possibility that it follows the general gymnotiform pattern of eggs scattered among cover with no substantial care afterward.
In the aquarium
Sternarchorhynchus inpai is not established in the aquarium hobby; it is essentially a fish of the ichthyological literature rather than the fishkeeping trade, and there is no meaningful body of hobbyist husbandry experience to draw on. Should specimens ever appear in the trade, the general precautions that apply to all ghost knifefishes would hold: as a scaleless gymnotiform it would be expected to be sensitive to ammonia, nitrite and nitrate, intolerant of copper-based medications, and to need dim lighting, secure cover and warm, soft, gently-flowing water to feel settled, since it is a nocturnal, electrosensory hunter rather than a fish that relies on sight. None of this is confirmed husbandry data for the species itself, and it should be treated as inference from its relatives rather than a tested care protocol.
Conservation
Sternarchorhynchus inpai is assessed by the IUCN as Vulnerable, an assessment made on 7 November 2018 under criterion D2, which applies to species with a very restricted area of occupancy or number of locations that leaves them susceptible to sudden threats. This pattern is common among the many narrow-range Sternarchorhynchus species described in the 2010 revision, several of which are known only from limited stretches of Amazonian river systems in Brazil.
Specific pressures on this species are not detailed in the sources available, but Amazonian basin species with restricted ranges are generally exposed to habitat alteration from damming, deforestation, mining-related pollution and mercury contamination. No population trend or targeted conservation measures are documented for S. inpai specifically.