Taxonomy & naming
Sternarchorhynchus mareikeae was described by de Santana and Vari in 2010 and belongs to the family Apteronotidae, the ghost knifefishes, in the order Gymnotiformes — the New-World electric knifefishes. Within the family it sits in the genus Sternarchorhynchus, a group of tube-snouted ghosts placed in the subfamily Sternarchorhamphinae. The genus name combines Sternarchus (an older genus name for related electric fish) with the Greek rhynchos, snout, referring to the long, downward-curving tubular snout that sets these fish apart from other apteronotids. The species epithet mareikeae honors the German biologist Mareike Roeder.
As a member of Gymnotiformes, S. mareikeae shares the order's defining trait: nearly all species, this one included, generate a weak electric organ discharge (EOD) around the body, used for electrolocation in the dark and for communication with other knifefish. Within Apteronotidae the electric organ is built from modified nerve cells rather than muscle, producing a fast, continuous wave-type discharge — the most refined electrosensory system in the order. The New-World knifefishes are not related to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus), a case of convergent body shape rather than kinship. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Like other ghost knifefishes, Sternarchorhynchus mareikeae has a blade-shaped, laterally compressed body with no dorsal fin and no true tail fin; a single long anal fin running most of the underside provides propulsion, allowing the fish to glide forward or backward with equal control. The skin is scaleless, a trait shared across the family that makes these fish sensitive to poor water quality and to certain medications.
The genus's hallmark is its snout: long, tubular and distinctly decurved, an adaptation for probing into sediment and crevices on the riverbed in search of buried prey. FishBase records males reaching about 7.5 in total length and females a smaller 5.5 in, a size difference that appears to be a genuine sexual dimorphism in this species rather than measurement noise, though the underlying biology of that difference is not documented. As in other Apteronotidae, an electric organ runs along the body beneath sensory pores that detect the self-generated field, giving the fish a functional picture of its surroundings independent of eyesight.
Habitat
Sternarchorhynchus mareikeae is known only from its type locality in Brazil; no other populations have been documented, and the species appears to be a narrow-range endemic rather than a widely distributed fish. Data on the specific river or drainage beyond "Brazil" is sparse in the sources available.
The genus as a whole is found in tropical freshwater river basins across South America, where its tube-snouted members forage over the riverbed. Members of the family favor warm, flowing, often dimly lit or tannin-stained water, conditions in which an electric sense is a far more useful tool than eyesight — consistent with the nocturnal, sediment-probing habits typical of the genus.
Feeding
Specific dietary data for Sternarchorhynchus mareikeae is not available in the sources reviewed, but the genus's feeding ecology is reasonably well characterized: Sternarchorhynchus species use their long, decurved snout to probe into the riverbed and among debris, taking aquatic insect larvae and other small invertebrates that burrow into the substrate. Prey is located primarily by electrolocation, detecting the faint electrical signature of animals hidden from sight in sediment or cover.
As with other apteronotids, feeding activity in this genus is expected to be concentrated after dark, when the fish's electric sense gives it a clear advantage over sight-hunting competitors. No aquarium feeding data exists for this species, as it is not known to be kept in captivity.
Mating
No species-specific courtship or spawning behavior has been documented for Sternarchorhynchus mareikeae. In ghost knifefishes generally, the wave-type electric organ discharge functions as more than a sensory tool: it carries information about a fish's identity, sex and reproductive state, and in the best-studied genus, Apteronotus, males and females are known to shift their discharge frequency during courtship in a kind of electrical exchange. It is reasonable to expect a broadly similar role for electric signalling in Sternarchorhynchus, but this has not been confirmed for the genus or for this species, and the point should be treated as inference from relatives rather than established fact.
Data on spawning behavior, timing, or site selection in S. mareikeae is sparse to nonexistent in the available literature.
Breeding
Breeding biology for Sternarchorhynchus mareikeae is essentially undocumented. Like other Apteronotidae, it is presumed to be an egg-layer, but no observations of spawning, egg deposition, or parental behavior have been published for this species. Ghost knifefishes are only rarely bred even in captivity, and this species has no aquarium history at all, so nothing further can be said with confidence — data sparse, and parental care is not documented in either direction.
In the aquarium
Sternarchorhynchus mareikeae is not known to be present in the aquarium trade. Most Sternarchorhynchus species are deep-channel Amazonian and South American river fish rarely, if ever, collected for the hobby, in contrast to the popular black ghost (Apteronotus albifrons) and its close relatives.
Were a tube-snouted Sternarchorhynchus ever to appear in captivity, the general care principles that apply across ghost knifefishes would be the starting point: warm, soft, near-neutral to acidic water; dim lighting and secure cover to suit a nocturnal, electrosensory fish; scrupulous water quality given the species' scaleless skin; and great caution with medications, avoiding copper-based treatments and reducing standard doses. Given the total absence of husbandry data for this specific species, none of this should be taken as tested guidance — it is inference from the family, not from experience with S. mareikeae itself.
Conservation
Sternarchorhynchus mareikeae is assessed as Vulnerable (VU) on the IUCN Red List, under criterion D2, reflecting its very restricted range — it is known only from its type locality in Brazil, with no other confirmed populations. A species known from a single location is inherently exposed to any localized habitat change, whether from pollution, damming, or land-use change in that river system, even though no specific threat has been documented in the assessment summary available.
Because the species has not been recorded elsewhere despite museum and survey work in South American river basins, its Vulnerable status is driven by range restriction rather than by observed population decline. Further survey work across nearby drainages would help clarify whether the species is truly this narrowly distributed or simply under-recorded.