Taxonomy & naming
Eigenmannia zenuensis was formally described in 2020 by Herrera-Collazos, Galindo-Cuervo, Maldonado-Ocampo and Rincón-Sandoval in Neotropical Ichthyology, using an integrative approach that combined osteology, geometric morphometrics and COI gene sequencing to separate it from its close relatives. It belongs to the family Sternopygidae — the glass and rattail knifefishes — within the order Gymnotiformes, the New-World electric knifefishes. These are bony fish, but unusual ones: Gymnotiformes are defined by an electric organ run the length of the body and by a single long anal fin that does almost all the swimming, letting the fish move backward as readily as forward. Despite the shared common name, they are unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance is convergent, not a matter of kinship.
Within the genus Eigenmannia, the new species was placed in the Eigenmannia trilineata species group, one of several complexes that a wave of taxonomic revision between 2015 and 2020 split apart — the group alone now holds thirteen recognised species, and the genus as a whole has grown from roughly ten species to about twenty-five as cryptic, narrow-range forms have been teased apart by exactly this kind of DNA-plus-morphology work. The species epithet honours the Zenú, the Amerindian people who historically inhabited the San Jorge River basin where the fish occurs. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for the valid name.
Morphology
Eigenmannia zenuensis is built like other glass knifefish: a long, laterally compressed, almost transparent body tapering to a fine point, with no dorsal fin and no true tail fin. Propulsion comes from a long ribbon-like anal fin running most of the underside of the body, thrown into a continuous travelling wave that drives the fish forward or backward with equal control — the same swimming style that lets these fish hold perfectly still or reverse out of a hiding spot without turning around. The type description records total lengths from about 6–12 in across the type series, and the species is distinguished from close relatives by fine details of dentition (56–60 teeth on the dentary in four to five rows, and seven teeth on the upper pharyngeal plate) alongside the genetic and morphometric evidence used to erect it.
As in all Sternopygidae, the skin is scaleless, and an electric organ running along the body drives a continuous, wave-type electric organ discharge — a steady low-voltage hum, rather than the pulsed discharges of some other gymnotiform families. Sensory pores across the head and body read the distortions in that self-generated field, giving the fish an electrolocation sense that substitutes for vision in dark or turbid water. External sexual dimorphism has not been documented for this species.
Habitat
The species is known from the lower Magdalena, Cauca and San Jorge river basins in northwestern Colombia, within the Depresión Momposina — a roughly 24,404 mi² active sedimentary lowland spanning the departments of Córdoba, Sucre, Bolívar, Magdalena and Cesar where these rivers converge and seasonally flood. It is, so far as described, endemic to Colombia and restricted to this single basin complex, which places it among the many gymnotiforms that are narrow-range, single-drainage specialists rather than continent-wide generalists.
The Depresión Momposina is characterised by slow-flowing tributaries, backwaters and seasonally inundated wetlands, often tannin-stained and dimly lit — exactly the kind of low-visibility water where a wave-type electric sense earns its keep. Like other glass knifefish, E. zenuensis most likely favours slow current, submerged roots and marginal vegetation over open channel, though detailed habitat use for this particular species has not been published; much of what can be said about its wild ecology is inferred from the genus rather than observed directly in this species.
Feeding
No species-specific dietary study has been published for Eigenmannia zenuensis, so its diet is inferred from the genus and family. Glass knifefish are nocturnal micro-predators that forage after dark using electrolocation to find small invertebrates — insect larvae, small crustaceans and similar prey — hidden in sediment, leaf litter or among roots, in water too dark or turbid for vision to be much use. They are not ambush hunters but active, probing foragers that work over cover methodically through the night.
Because the prey items involved are small, glass knifefish are generally peaceful toward tankmates too large to be swallowed, even while they remain efficient nocturnal predators of anything smaller. Nothing in the available sources suggests E. zenuensis departs from this pattern, but the specifics — prey composition, foraging range, seasonal diet shifts — remain data sparse for this species.
Mating
Courtship in Eigenmannia is inseparable from its electric sense. The wave-type discharge that the genus uses for electrolocation also carries information about sex and identity, and Eigenmannia species — most famously the widely studied glass knifefish used in neuroscience research — show sex-specific discharge frequencies and the classic jamming avoidance response, in which two fish with similar discharge frequencies shift them apart to avoid interference with each other's electrolocation. That electrical exchange is thought to structure encounters between individuals, including courtship, though the fine behavioural detail has been worked out mostly in laboratory Eigenmannia rather than in the wild or in E. zenuensis specifically.
Beyond the electrical signalling, no courtship behaviour has been documented for this species. As with much of its biology, what is known is extrapolated from better-studied relatives in the same genus and family rather than observed directly.
Breeding
Eigenmannia zenuensis has not been reported to breed in captivity, and its wild reproductive ecology is unstudied. What is known comes from the family: Sternopygidae are egg-layers that scatter adhesive eggs among plant roots and floating or submerged vegetation, typically triggered by the warm, soft, rising water of the wet season, with little to no parental care afterward — the eggs are left among cover to develop unguarded. Within the genus, Eigenmannia species (including the widely traded glass knifefish, E. virescens) are among the more readily spawned gymnotiforms in captivity, but that track record does not extend to this narrow-range, recently described species, for which breeding data is simply absent from the literature.
For now, the honest statement is that E. zenuensis is a taxonomically documented fish whose reproductive biology remains to be studied, rather than a species with any established breeding protocol, wild or captive.
In the aquarium
Eigenmannia zenuensis does not appear to be established in the aquarium trade; the available sources describe it only as a recently named, narrow-range wild species, with no hobby literature, husbandry reports or import records located. Any aquarium guidance has to be drawn from the genus and family rather than from experience with this species itself.
Glass knifefish in general do reasonably well in captivity relative to other gymnotiforms — they can be kept in a small shoal, tolerate community conditions better than the more predatory genera, and are a classic subject of electrophysiology research for exactly that reason. General Sternopygidae care calls for warm (roughly 73–82 °F), soft to moderately mineralised, near-neutral to slightly acidic water, dim lighting, and plenty of cover such as roots or plants for a fish that is most active at night. Being scaleless, the family is sensitive to ammonia, nitrate and to copper-based or harsh medications, which should be used at reduced doses if at all. Given how little is documented for E. zenuensis specifically, none of this should be read as a tested protocol for the species — only as the reasonable starting point its relatives suggest, pending real husbandry data.
Conservation
Eigenmannia zenuensis has not been formally assessed by the IUCN; its status is treated as Data Deficient given both the recency of its description and its very restricted range. It is currently known only from the lower Magdalena, Cauca and San Jorge basins within the Depresión Momposina of northwestern Colombia — a single, tightly bounded sedimentary lowland rather than a continent-spanning range.
That narrow distribution is the species' main point of vulnerability. Single-basin Neotropical endemics of this kind are typically most exposed to localized pressures — habitat alteration, water pollution, and the cumulative effects of agricultural and hydrological change across the Magdalena–Cauca system, one of Colombia's most heavily modified river networks. No population trend or specific threat has yet been quantified for E. zenuensis in the literature, and further field study would be needed before any conservation status beyond Data Deficient could be assigned with confidence.