Taxonomy & naming
Rhabdolichops jegui was described by Keith & Meunier in 2000 and placed in the family Sternopygidae, the glass and rattail knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Gymnotiformes are bony fish, but unusual ones: nearly every species generates a weak electric organ discharge (EOD) around its body, used for electrolocation in the dark and for communication with other knifefish, and the group is defined as much by that electric sense and its ribbon-like anal fin as by conventional anatomy.
The genus Rhabdolichops sits within Sternopygidae alongside the better-known glass knifefish (Eigenmannia) and rattail knifefish (Sternopygus), and its members are mostly open-water or deep-channel fish, several of them narrow-range and poorly studied. The species epithet honours the ichthyologist Michael Jégu of ORSTOM (the French research institute now IRD), reflecting the strong French Guianese thread running through its discovery. As with all Gymnotiformes, R. jegui is entirely unrelated to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus) — the resemblance is convergent body shape, not kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
Rhabdolichops jegui reaches a maximum of about 12.5 in in total length. It has the classic Sternopygidae build: a long, laterally compressed, ribbon-like body that is grey and slightly translucent, with a darker dorsum and hyaline (glassy, near-transparent) fins. As in all its relatives, there is no dorsal fin and no distinct tail fin — locomotion comes from a single elongated anal fin running along most of the underside, rippled in travelling waves that let the fish glide forward or backward with equal ease.
The body carries the electric organ along its length and an array of skin pores that read the field it produces, and like other gymnotiforms the species is scaleless, which leaves it with little physical protection and considerable sensitivity to poor water quality. R. jegui produces a wave-type electric organ discharge — a continuous, tone-like signal typical of Sternopygidae, in contrast to the intermittent pulse-type discharge of families such as Gymnotidae.
Habitat
The species is known from the Maroni River basin in French Guiana, on the Guiana Shield coast of northern South America. It is a bottom-associated fish of relatively deep water, recorded in the main river channels as well as floodplains and lagoons connected to them, rather than in shallow margins.
Other species in the genus Rhabdolichops show a range of water-chemistry preferences — some, such as R. nigrimans and R. navalha, favour low-conductivity blackwater systems, while R. lundbergi is found in higher-conductivity whitewater main channels — and R. jegui's presence in the Maroni fits the broader genus pattern of deep-channel, open-water Neotropical river life. As with other Sternopygidae, this is warm, typically soft to moderately mineralised water where daylight penetrates poorly and an electric sense is far more useful than eyesight for finding prey and avoiding obstacles.
Feeding
Detailed dietary data for Rhabdolichops jegui specifically are not documented in the available sources. Based on the ecology of Sternopygidae generally, it is reasonable to expect a nocturnal micro-predator diet of small benthic invertebrates — aquatic insect larvae, worms and small crustaceans — located by electrolocation in the dark river channels it inhabits, in keeping with the family's peaceable, small-prey feeding style toward anything too large to swallow.
As an open-water, deep-channel species that is essentially unknown in captivity, there are no aquarium feeding reports to draw on, and the point should not be overstated: this is inference from its relatives and habitat rather than a documented feeding record for the species itself.
Mating
Courtship in Sternopygidae is closely tied to their wave-type electric discharge. In the family generally, males defend a territory and raise their EOD rate to advertise and attract females, and the discharge frequency itself functions as a signature of species and sex, a mechanism best documented in the familiar glass knifefish (Eigenmannia), whose electric signalling and jamming-avoidance response are a classic study system in neuroscience. It is reasonable to expect R. jegui to court in a broadly similar way, using its own wave-type discharge, though this has not been directly documented for the species.
No species-specific courtship behaviour has been recorded for Rhabdolichops jegui in the available literature; what can be said with confidence is limited to the general pattern for its family, and the specifics for this particular species remain data sparse.
Breeding
Rhabdolichops jegui has not been reported bred in the aquarium, and its reproduction in the wild is not well documented. Sternopygidae in general are egg-layers that scatter adhesive eggs among aquatic plant roots or floating vegetation, typically spawning under warm, soft-water, wet-season conditions with a rise in water level; in captive Eigenmannia, breeding has been coaxed by simulating that seasonal shift — raising the water level, then lowering pH and temperature. Parental care across the family is minimal: eggs are left among vegetation with no significant guarding.
Whether R. jegui follows this pattern precisely is unconfirmed — the species is essentially unstudied on this point, and given how rarely it is seen at all, the honest position is that its breeding biology is poorly documented rather than a known protocol.
In the aquarium
Rhabdolichops jegui is not an established aquarium fish; it is a scientifically described but obscure species from a remote, single-basin range, and it does not appear in the ornamental trade in any meaningful way. Any care notes have to be extrapolated from Sternopygidae in general, with the usual caveats that apply to gymnotiforms: being scaleless, they are sensitive to ammonia and nitrate and require particular care with medications, since copper-based treatments and standard doses of many other compounds can be harmful and typically call for reduced dosing.
As a nocturnal, electrolocating predator of a deep river channel, a fish of this kind would need dim lighting, ample cover, and stable, mature water quality, and would not be considered safe with bite-sized tankmates. In practice, though, this is a species best appreciated as part of the broader Sternopygidae story rather than one to plan a tank around.
Conservation
Rhabdolichops jegui is assessed by the IUCN as Near Threatened, with the most recent assessment dated 14 December 2022. Its entire known range lies within the Maroni River basin of French Guiana, a narrow single-basin distribution that leaves it more exposed than the wide-ranging Gymnotiformes species found across multiple major Amazonian and Guiana Shield rivers.
As with other narrow-range Neotropical freshwater fish, the pressures most likely to matter for a species confined to one river system are habitat change, water-quality decline and disturbance of the deep-channel and floodplain habitats it depends on, though specific documented threats for R. jegui are not detailed in the available sources. Its restricted range alone is enough to warrant a more cautious status than its wider-ranging relatives, without overstating threats that have not been directly documented for this species.