Taxonomy & naming
Rhabdolichops navalha was described by Correa, Crampton & Albert in 2006, one of three new Rhabdolichops species named together from the lowland Central Amazon in a paper published in Copeia. It belongs to the family Sternopygidae — the glass and rattail knifefishes — within the order Gymnotiformes, the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: they are defined by an electric organ and a ribbon-like anal fin rather than by the fin arrangement of typical aquarium fish, and nearly all of them generate a weak electric organ discharge (EOD) that they use both to electrolocate prey and obstacles in the dark and to communicate with each other.
Within the family, R. navalha is phylogenetically nested with R. stewarti, R. eastwardi, R. caviceps and R. troscheli, and the original description singled it out on the basis of an unusual electric organ. Despite the shared common name "knifefish", the Gymnotiformes are entirely unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus) — those are bonytongues from a different order, and the resemblance in body shape is convergent, not a sign of kinship. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Rhabdolichops species are built for open water: a very long, slender, laterally compressed body with a semi-transparent, glassy quality typical of the genus, tapering into an elongated tail. As in every Sternopygidae, there is no dorsal fin and no ordinary tail fin — locomotion comes almost entirely from a single, very long anal fin that runs along most of the underside of the body, thrown into travelling waves that drive the fish forwards or backwards with equal ease. The skin is scaleless.
The feature that distinguishes R. navalha from its closest relatives is its electric organ: rather than running the full length of the tail as in most Sternopygidae, the organ's posterior margin ends abruptly partway down the body, and the tissue beyond that point is rigid and non-electrogenic rather than tapering off gradually. This wave-type electric organ produces a continuous, near-sinusoidal discharge, the signature "hummer" pattern of the family, used for electrolocation and communication. Reported size for the species is in the region of 12 in total length, broadly typical for the genus, though comprehensive size data for R. navalha specifically is sparse.
Habitat
Rhabdolichops navalha is known from the lowland Central Amazon basin in Brazil, recorded from low-conductivity blackwater systems — the soft, acidic, tannin-stained rivers typical of much of the Amazon interior. Species in this genus, along with the related Distocyclus, are generally open-water or deep-channel fish rather than the root-tangle and leaf-litter specialists seen among Sternopygus and Eigenmannia, and detailed habitat data specific to R. navalha remains sparse beyond its documented blackwater, low-conductivity range.
Blackwater of this kind is warm, extremely soft and nearly opaque with dissolved tannins, conditions where eyesight is of limited use and an electric sense becomes the primary way to navigate and find food. This is consistent with the broader pattern across Gymnotiformes, whose distribution is confined entirely to Neotropical fresh waters of South and Central America — the Amazon, Orinoco, Guianas, Paraná–Paraguay and, for a few species, the trans-Andean Magdalena and Maracaibo systems.
Feeding
Specific dietary data for Rhabdolichops navalha is limited, but the original description notes it feeding on aquatic invertebrates including copepods, consistent with the broader pattern in Sternopygidae of nocturnal micro-predation on small invertebrates located by electrolocation rather than sight. Like other glass and rattail knifefishes, it is best understood as a dark-water hunter that reads the electrical distortions produced by prey and obstacles rather than relying on vision.
Across the family, this translates in captivity to a preference for small live and frozen meaty foods offered after dark, though husbandry information for R. navalha itself is essentially undocumented — it is not an established aquarium species, and generalisations here are drawn from its better-known Sternopygidae relatives rather than from direct observation of this species.
Mating
No specific courtship or mating behaviour has been documented for Rhabdolichops navalha. Across Sternopygidae generally, the wave-type electric organ discharge that the family uses for electrolocation also carries information used in courtship and rivalry — most thoroughly documented in the glass knifefish Eigenmannia, where males and females hold sex-specific discharge frequencies and use the well-studied jamming avoidance response to keep their signals distinct from one another and from rivals. It is reasonable to expect a broadly similar electric-signalling basis to courtship in Rhabdolichops, but this has not been specifically studied or reported for R. navalha, and the point should be read as a family-level pattern rather than a confirmed fact about this species.
Breeding
Breeding biology for Rhabdolichops navalha is undocumented; this is a data-sparse, non-aquarium species with no reported spawning observations, wild or captive. Sternopygidae in general are egg-layers that scatter adhesive eggs among plant roots or floating vegetation, typically cued to the warm, soft, higher-water conditions of the wet season, with little to no parental care afterwards — a pattern well established in Eigenmannia, the family's most frequently bred genus in captivity. Whether R. navalha follows this pattern closely has not been confirmed; nothing beyond the general family pattern can be stated with confidence for this species.
In the aquarium
Rhabdolichops navalha is not an established aquarium fish and is essentially unknown in the hobby; there is no reliable record of it being kept or traded. What follows is drawn from the general requirements of Sternopygidae rather than from direct experience with this species. Being scaleless, family members require careful use of medications — no copper-based treatments, and reduced doses of anything else — along with vigilant control of ammonia and nitrate, to which scaleless fish are unusually sensitive. As nocturnal, electrolocating predators they need dim lighting and secure cover to feel settled by day, and they are generally not safe with bite-size fish or shrimp that can be hunted after dark.
Water should be warm (around 73–82 °F), soft to moderately mineralised, and near-neutral to acidic, ideally with the tannin-stained, dimly lit character of the fish's blackwater home, which also suits its electric sense better than brightly lit, clear-water setups. Given how little is documented about this species specifically, and its apparent restriction to remote blackwater habitat, it is best treated as a fish for specialist or research contexts rather than a realistic community or display aquarium candidate.
Conservation
Rhabdolichops navalha is assessed as Least Concern on the IUCN Red List. As with many gymnotiforms, this reflects the species occupying suitable Central Amazon blackwater habitat that remains extensive rather than any detailed population survey, and narrow-range or single-basin endemics in this family are generally the ones most exposed to habitat change, damming, pollution and deforestation pressure across the Amazon.
There is no evidence of significant trade or collection pressure on this species — it does not appear to be part of the ornamental fish trade — so its main long-term exposure, in common with other Central Amazon blackwater specialists, would be broader degradation of the low-conductivity river systems it depends on rather than any pressure specific to the species itself.