Taxonomy & naming
Apteronotus magdalenensis was described by Miles in 1945, originally placed in the now-abandoned genus Ubidia as Ubidia magdalenensis. Albert & Campos-da-Paz reassigned it to Apteronotus sensu stricto in 1998 following a cladistic revision of the ghost knifefishes, and it has stood in that genus since. It belongs to the family Apteronotidae within the order Gymnotiformes, the New-World electric knifefishes — bony fish, but unusual ones, defined by an electric organ and a single long ribbon-like anal fin rather than a conventional fin arrangement. The Apteronotidae are set apart within the order by an electric organ built from modified nerve cells rather than muscle, producing a fast, high-frequency wave-type discharge used for electrolocation and communication in the dark.
The genus name Apteronotus comes from the Greek a- ('without') plus pteron ('fin') plus notos ('back') — 'lacking a dorsal fin', a reference to the family's missing dorsal (in place of which they carry a fleshy dorsal filament). The species epithet magdalenensis refers to the río Magdalena, the Colombian basin to which the species is endemic. As with the rest of the order, these are not related to the Asian featherback or clown knifefishes (Chitala, Notopterus) despite the shared common name — the resemblance is convergent body shape, not kinship. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
Morphology
Apteronotus magdalenensis reaches up to about 17.5 in total length in males and 14.5 in in females, a substantial size for the genus, though it is far less studied than the black ghost. FishBase records a marbled, pale coloration patterned with brown blotches, distinct from the uniform velvety black of A. albifrons — a useful field mark where the two might otherwise be confused by common name alone. Older literature that cites lengths around 51 in for this species is a documented mix-up with the unrelated Sternopygus aequilabiatus and should not be taken as fact for A. magdalenensis.
Like other ghost knifefishes it has no true dorsal or tail fin; locomotion runs almost entirely off a long anal fin thrown into travelling waves, letting the fish move forward or backward with equal ease. The body is laterally compressed and scaleless, and an electric organ runs along its length, paired with sensory pores across the skin that read the field it generates. Sexual dimorphism is not well documented for this species beyond the size difference between the sexes reported by FishBase (males somewhat larger than females).
Habitat
This species is endemic to the río Magdalena-Cauca basin in northern Colombia, a trans-Andean drainage that runs separately from the Amazon and Orinoco systems that carry most of its Apteronotus relatives. It is a benthopelagic freshwater fish, recorded in warm water with habitat temperatures around 78–81 °F (average about 80 °F) in the basin. A 2009 distribution-extension record (Agudelo-Zamora et al., in Check List) confirmed additional localities within the basin, describing the species as poorly known.
As with other ghost knifefishes, dim or turbid water suits its electrosensory lifestyle far better than clear, brightly lit habitat — electrolocation is most useful precisely where eyesight is not. Specific data on substrate, flow, and vegetation associations for this species are sparse in the available literature; broader Apteronotidae habitat patterns (river channels, submerged roots, leaf litter) likely apply but are not confirmed for A. magdalenensis specifically.
Feeding
Detailed dietary studies specific to Apteronotus magdalenensis are not available in the sources reviewed. By analogy with the well-studied black ghost knifefish and other Apteronotidae, it is reasonable to infer a nocturnal carnivorous habit — hunting small benthic invertebrates such as insect larvae, worms and small crustaceans, located largely through electrolocation in dark or turbid water — but this has not been confirmed by direct observation of A. magdalenensis and should be treated as data sparse rather than established fact for this particular species.
Mating
No species-specific courtship data for Apteronotus magdalenensis were found in the sources reviewed. Across the ghost knifefishes, the wave-type electric organ discharge is known to carry information about a fish's identity, sex and readiness to spawn, and in the well-studied brown ghost (A. leptorhynchus) males and females shift discharge frequency in an electrical duet during courtship. It is plausible that A. magdalenensis courts in a broadly similar way, given its shared family-level electrosensory biology, but this has not been documented for the species itself — data sparse.
Breeding
Breeding biology for Apteronotus magdalenensis is essentially undocumented. There is no record of the species being bred in captivity, and given how rarely even the trade-familiar black ghost knifefish spawns in home aquaria, and that A. magdalenensis barely appears in the ornamental trade at all, any account of a breeding protocol would be invention. What can be said with confidence, by family-level inference, is that Apteronotidae are egg-layers that spawn among cover such as roots and crevices, without substantial parental care afterward — but this is inferred from relatives, not observed directly in this species.
In the aquarium
Apteronotus magdalenensis is not an established aquarium fish — it does not appear to be part of the ornamental trade, and there is no meaningful hobbyist husbandry record to draw on. Any fishkeeping guidance here would necessarily be extrapolated from its better-known relative, the black ghost knifefish: as a scaleless, nocturnal, electrosensory predator it would need dim lighting, secure cover such as caves or tubes, warm soft water, and great care with medications (no copper-based treatments, reduced doses generally). Given its restricted native range and apparent scarcity, keeping this species is not something the hobby should expect to encounter, and any specimens that did surface would be best left to specialist or conservation-oriented keepers rather than general fishkeeping.
Conservation
The IUCN Red List assesses Apteronotus magdalenensis as Least Concern, an assessment last updated in 2014 per FishBase and reaffirmed in the 2022 Red List cycle. That status sits in tension with Colombia's own Red Book of Freshwater Fishes, which lists the species as Vulnerable under Category C, citing its restricted single-basin range, the scarcity of capture records in the roughly 57 years since its description, and a broader lack of ecological data to assess it confidently. The species is endemic to the río Magdalena-Cauca basin, a heavily modified drainage subject to substantial human pressure from agriculture, damming and pollution, which makes the national Vulnerable listing a reasonable caution even where the global IUCN assessment currently reads more optimistically. Until more field data accumulates, the honest summary is a poorly known, narrow-range endemic whose true conservation status remains uncertain.