Taxonomy & naming
Sternarchorhamphus muelleri was described by Franz Steindachner in 1881 and is the sole member of its genus, placed in the subfamily Sternarchorhamphinae within the family Apteronotidae, the ghost knifefishes, in the order Gymnotiformes — the New-World electric knifefishes. Like every gymnotiform it is a bony fish but an unusual one, defined by an electric organ and a single long ribbon-like anal fin rather than by scales, a dorsal fin, or a conventional tail.
Apteronotidae is set apart within Gymnotiformes by an electric organ built from modified nerve tissue rather than muscle, which produces a fast, continuous wave-type discharge — the most refined electrolocation system in the order. The family's common name, "ghost knifefish", and the superficial resemblance of its members to the unrelated Asian featherback and clown knifefishes (Chitala, Notopterus) is convergence, not kinship; those are bonytongues in an entirely different lineage. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name Sternarchorhamphus muelleri.
Morphology
The defining feature of Sternarchorhamphus muelleri is its snout: elongated and tubular, curving downward into a small terminal mouth, a shape shared with only a handful of other apteronotids (the tube-snouted Sternarchorhynchus) and adapted for probing into sediment and crevices for buried prey. The body is the typical ghost-knifefish blade — deep and strongly compressed side to side, tapering to a slender tail with no separate tail fin and no dorsal fin at all. FishBase records a maximum total length of about 18 in, making it one of the larger apteronotids.
As in the rest of the family, propulsion comes almost entirely from a very long anal fin running beneath the body, rippled in travelling waves that let the fish move forward or backward with equal ease. The skin is scaleless and carries the sensory pores that read the electric field generated along the body. It is a benthopelagic fish, living and foraging near the river bed. Sexes are not distinguished by any documented external character; dimorphism data is sparse for this species.
Habitat
This is a fish of the deep channels of major Amazonian rivers, recorded across an unusually wide span of the basin — the middle and lower Madeira, the Juruá, Ucayali, Negro, Branco, Trombetas and Capim rivers, the main Amazon channel itself, and the Araguari–Macari–Amapá system near the river's mouth — as well as the Orinoco basin to the north, from its lower reaches up through the Apure and into the upper Orinoco. The distribution crosses the Vaupés Arch, the low sedimentary divide that separates the Amazon and Orinoco drainages, making it one of the relatively few gymnotiforms found on both sides.
Adults are associated with deep river channels rather than shallow margins, while the floodplain várzea and its floating meadows appear to serve as a nursery habitat for eggs and young. Like other apteronotids it is a fish of warm, dim, often turbid or tannin-stained water where an electric sense does far more work than eyesight.
Feeding
Sternarchorhamphus muelleri forages along the river bed for aquatic insect larvae, using its long, curved, tubular snout to probe into the substrate and among cover where prey hides. As in other ghost knifefishes, this benthic hunting is guided largely by electrolocation: the fish's own weak electric field is distorted by anything nearby, letting it detect buried or hidden prey in the dark or turbid water it inhabits without relying on sight.
Specific dietary data beyond this benthic insect-larvae foraging pattern is sparse for the species; detailed stomach-content or feeding-behaviour studies do not appear in the sources reviewed here, and nothing is documented about its feeding in aquaria, where it is essentially unknown in the trade.
Mating
As in other Apteronotidae, the wave-type electric organ discharge of Sternarchorhamphus muelleri very likely carries information used in courtship and individual recognition — this is a well-established pattern across the family, in which discharge frequency and waveform encode species, sex and identity, and rivals or prospective mates exchange signals electrically before any physical approach. No species-specific courtship description exists in the sources reviewed here, so this should be read as inference from the family's general biology rather than an observed account for S. muelleri.
The use of várzea floodplain floating meadows as an apparent nursery for eggs and larvae suggests spawning takes place in or near these seasonally flooded margins rather than in the deep channels adults otherwise occupy, but the details of pairing, timing and site selection are not documented.
Breeding
Sternarchorhamphus muelleri is oviparous, like all apteronotids, but its breeding biology is poorly documented and it is not known to be bred in captivity — this is a wild-collected, deep-channel species essentially absent from the aquarium trade. The one specific clue in the record is that floodplain várzea floating-meadow habitat appears to function as a nursery for eggs and larvae, implying that spawning is tied to the seasonal flood pulse rather than happening in the main channel.
No parental care is documented, consistent with the rest of the family. Given the total absence of aquarium-breeding reports, this account prefers to say plainly that the species' reproduction is data sparse rather than to construct a protocol that does not exist in any source.
In the aquarium
Sternarchorhamphus muelleri is not an aquarium fish in any practical sense — it is a deep-channel Amazonian and Orinocan species known mainly from ichthyological survey and systematics work, not from the ornamental trade, and no husbandry record for it exists in the sources reviewed here. Any aquarist who did encounter one would need to apply the general rules for ghost knifefishes: it is scaleless and therefore sensitive to ammonia, nitrate, and to copper-based or harsh medications, which should be avoided or heavily reduced; it is a nocturnal, electrolocating benthic predator with a long, delicate tubular snout, needing a large, dimly lit tank with soft substrate and secure cover rather than bright light and bare décor.
Its specialised tube-snout, its large adult size (to roughly 17.5 in total length), and its deep-channel habits make it a poor fit for typical home aquaria even among ghost knifefish specialists. This is a species to know about and respect in its native rivers, not one to expect to keep.
Conservation
The IUCN Red List assesses Sternarchorhamphus muelleri as Least Concern. It is the only species in its genus, and its documented range is unusually broad for a gymnotiform, spanning the Amazon basin from the Madeira and Juruá in the west to the Amazon's mouth in the east, and reaching north across the Vaupés Arch into the Orinoco basin as far as the upper Orinoco and Apure rivers. No specific threat assessment is detailed in the available sources; the wide, multi-basin distribution is itself the basis for a stable, low-concern status.
As with other wide-ranging Amazonian and Orinocan fish, the general pressures on the region — damming, deforestation, and pollution including mercury from mining — are the backdrop threats to watch, but nothing in the record singles out S. muelleri as a species under active decline.