Taxonomy & naming
Apteronotus mariae was described by Eigenmann and Fisher in 1914 and belongs to the family Apteronotidae, the ghost knifefishes, within the order Gymnotiformes — the New-World electric knifefishes. Like its relatives it is defined less by fins and scales than by an electric organ, in this family built from modified nerve tissue rather than muscle, which gives the Apteronotidae the fastest, highest-frequency wave-type discharges in the order.
The species' identity was muddled for decades against Apteronotus jurubidae (Fowler, 1944), a name based on material from the Pacific slope of Colombia; a taxonomic redescription clarified the type locality, morphology and valid status of A. mariae and resolved its relationship to A. jurubidae. The specific epithet honours Brother Apolinar María, a Colombian Christian-brother missionary and naturalist who collected extensively in Colombia in the early twentieth century. The Catalog of Fishes is the authority for the valid name. As with other Gymnotiformes, A. mariae is unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus), whose similar shape is convergent, not a sign of kinship.
Morphology
Apteronotus mariae shows the family's characteristic blade-like, laterally compressed body, reaching about 10.5 in in standard length, with a long anal fin running most of the length of the underside and no dorsal or true tail fin in the conventional sense. Fin-ray counts recorded for the species run to 162–180 soft rays in the anal fin, the structure that provides essentially all of its propulsion, rippling in travelling waves to drive the fish forwards or backwards with equal ease.
The skin is scaleless, as in all ghost knifefishes, and studded with electroreceptor pores that read the electric field generated by the fish's own electric organ. Data on colour pattern and external sexual differences are sparse for this species; no dimorphism has been documented in the sources available.
Habitat
The species is a Magdalena River basin endemic, restricted to Colombia — a distribution far narrower than that of its widespread relative the black ghost knifefish (A. albifrons), which ranges across the Amazon, Orinoco and Paraná systems. It occupies tropical freshwater habitat and is described as benthopelagic, living and feeding through the water column near the bottom rather than sitting directly on it.
As with other Apteronotidae, the electric sense is best suited to exactly the kind of water this genus favours: warm, often turbid or shaded river habitat where vision is of limited use and an electric field is a more reliable way to detect prey, obstacles and other fish. Specific water-chemistry data for A. mariae in the wild is not recorded in the available sources.
Feeding
Apteronotus mariae is assigned an intermediate trophic level (around 3.3), consistent with a carnivorous diet of small invertebrates and other prey typical of the family — aquatic insect larvae, worms and small crustaceans, most likely detected in the dark or turbid water of the Magdalena system largely through electrolocation rather than sight, as in its better-studied congeners.
Detailed field or aquarium diet records specific to this species are not available in the sources reviewed; feeding ecology is inferred from its trophic-level data and from the well-documented nocturnal, electroreceptive hunting behaviour shared across Apteronotidae.
Mating
No species-specific courtship observations for Apteronotus mariae are documented in the available sources. Across the Apteronotidae, however, the wave-type electric organ discharge is known to function as a social signal as well as a sensing tool, encoding a fish's identity, sex and readiness to spawn; in the closely related brown ghost knifefish (A. leptorhynchus), a congener studied in detail for its electrocommunication, males and females shift discharge frequency during encounters in an electrical exchange, and rival fish produce distinctive interruptions on meeting. It is reasonable to expect a broadly similar electric-signalling component to courtship in A. mariae, though this has not been directly studied in the species itself.
Breeding
Breeding biology for Apteronotus mariae is poorly documented; FishBase records breeding data as unavailable for the species, and no aquarium-spawning accounts appear in the sources reviewed. As an apteronotid it is presumed to be an egg-layer, in keeping with the rest of the family, most likely scattering eggs among cover such as roots or submerged vegetation, with no parental care recorded for the genus.
The species is essentially absent from hobbyist breeding literature, and there is no evidence it has been captive-bred; any fish reaching the trade would be expected to be wild-caught. Data sparse — no reliable breeding protocol should be inferred.
In the aquarium
Apteronotus mariae is not an established aquarium species; it does not appear to be regularly traded, and aquarium-specific husbandry data is not available in the sources reviewed. As with all scaleless Apteronotidae, any specimen that did reach the hobby would need the family's standard precautions: careful, reduced-dose medication with no copper-based treatments, meticulous control of ammonia and nitrate, and a dim, sheltered tank with secure hides reflecting its nocturnal, electrolocating habits.
Given its narrow endemic range and the near-total absence of trade or captive-husbandry records, this is a species best regarded as a scientific curiosity rather than an aquarium prospect at present; anyone who did encounter it should treat it as they would a wild-caught, poorly studied electric fish — cautious acclimation, minimal handling, and no assumption of compatibility with small tankmates given its family's nocturnal-predator habits.
Conservation
Apteronotus mariae is assessed as Least Concern on the IUCN Red List, an assessment dated 9 October 2014, and FishBase similarly reports low vulnerability to fishing pressure (23 out of 100). It is regarded as harmless to humans.
Despite the reassuring status, the species is a single-basin endemic, restricted to the Magdalena River system in Colombia — one of the country's most heavily modified river basins, subject to damming, pollution and land-use change. A narrow range of this kind means the Least Concern rating reflects the absence of a documented decline rather than a large or resilient population, and any future degradation of Magdalena River habitat would bear on this species specifically, even though it is not currently flagged as threatened.