Taxonomy & naming
Porotergus duende was described by de Santana and Crampton in 2010 as part of a revision of the genus Porotergus, published in the journal Copeia. It belongs to the family Apteronotidae — the ghost knifefishes — within the order Gymnotiformes, the New-World electric knifefishes. The Apteronotidae are distinguished within the order by an electric organ built from modified nerve cells rather than muscle tissue, which lets them generate the fastest, highest-frequency electric organ discharges of any knifefish; this wave-type signal underlies both their electrolocation and their social signalling.
The species epithet duende is Portuguese for an elf or household imp, chosen by the describing authors in reference to the fish's small size relative to its relatives in the genus. Porotergus duende is one of several species distinguished in that 2010 review by subtle differences in head profile, colour pattern and the lateral-line canal system; a more recent molecular phylogeny of the ghost knifefishes (Mendonça et al. 2025) has since confirmed it as a valid, genetically distinct species. As with all Gymnotiformes, it is unrelated to the Asian featherback and clown knifefishes (Chitala, Notopterus) despite the shared common name — the resemblance is convergent, not a sign of kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
Porotergus duende is a small, blade-bodied fish, reaching around 7 in total length in males and unsexed individuals, with females notably smaller at up to about 4 in — a size difference not typical of most Apteronotidae and one of the few tangible facts recorded about the species' biology. Its original description notes a steeply sloped forehead and a comparatively uniform body coloration, lacking the pale antorbital stripe seen in some related species, and it lacks an externally visible supratemporal lateralis canal, a feature used to separate it from its closest congeners.
As in other Apteronotidae, the body is strongly compressed side to side and tapers toward the tail, with no dorsal fin and propulsion supplied almost entirely by a long anal fin run as a travelling wave beneath the body. The species is scaleless, and an electric organ runs the length of the body beneath a field of electroreceptive pores in the skin. Sex is difficult to assess from museum material beyond the size disparity noted between the sexes; no distinct external dimorphic markings have been documented.
Habitat
The species is known from the western portion of the Amazon basin, recorded in the main channel of the Amazon River and its major tributaries, including the Rio Negro and Rio Solimões in Brazil and the Rio Ucayali in Peru. The type locality is a beach on Ilha Cuera near Tefé, on the Rio Solimões in Amazonas state, Brazil. Unlike some relatives that occupy varied channel habitats, P. duende is restricted to deep-channel habitat in the main river course rather than backwaters or floodplain lakes.
Water at these sites is warm and close to neutral, with FishBase reporting a pH range of roughly 6.9–7.3 and temperatures of 81–90 °F. As a deep-channel fish it lives in turbid, often fast-flowing water where visibility is minimal, the setting in which the electric sense that defines its order does its real work — sensing the riverbed, obstacles and other fish where eyes offer little help.
Feeding
No species-specific dietary study has been published for Porotergus duende. Based on the general biology of the Apteronotidae and its deep-channel habitat, it is reasonable to expect a nocturnal, benthic-foraging diet of small invertebrates — aquatic insect larvae, worms and small crustaceans — detected largely through electrolocation rather than sight, in keeping with its relatives in the family. This is inference from the family's known biology rather than a documented observation, and should be treated as such; the literature is data sparse on this point for this particular species.
No aquarium feeding records exist, since the species is essentially unrepresented in the hobby.
Mating
Courtship and spawning behaviour have not been documented for Porotergus duende specifically. What can be said with confidence draws on the broader biology of the Apteronotidae: the wave-type electric organ discharge that defines the family carries information about a fish's identity, sex and physiological state, and in the best-studied ghost knifefishes (species of Apteronotus) males and females are known to shift discharge frequency during courtship in an electrical exchange. It is plausible that similar electric signalling plays a role in how P. duende individuals locate and assess one another in the dark river channels they inhabit, but this has not been directly observed or published for the species.
Beyond that inference from family-level biology, mating behaviour in P. duende is unrecorded — data sparse.
Breeding
Breeding biology in Porotergus duende is essentially undescribed. The original 2010 description and the subsequent 2025 molecular study both note that the species remains poorly known in the literature and is rare or absent from the aquarium trade, meaning there is no husbandry record to draw on either. As an apteronotid it is presumed to be an egg-layer, in line with the rest of the family, but no spawning event, egg description or account of parental care has been published for this species.
Given this, the honest statement is that breeding in P. duende is rarely bred / poorly documented, rather than something with a known protocol. No parental care has been documented.
In the aquarium
Porotergus duende has essentially no presence in the aquarium hobby; it is a deep-channel Amazonian species collected in taxonomic and survey work rather than for the trade, and no husbandry accounts exist to draw on. Anyone who did encounter the species would need to apply the same baseline care that applies across the ghost knifefishes: warm, soft to moderately mineralised, near-neutral water reflecting its native river conditions (around 81–90 °F, pH close to neutral per FishBase records), dim lighting and secure cover to suit a fish adapted to dark, turbid channels, and no marine salt.
Because it is scaleless, like all Apteronotidae, it would be expected to be sensitive to ammonia and nitrate and to copper-based or harsh medications, which should be avoided or dosed conservatively. As a nocturnal electroreceptive predator it should not be assumed safe with small, bite-size tankmates. Given how little is known of the species, anyone acquiring it should treat husbandry as experimental and prioritise water quality and cover over any specific stocking recommendation.
Conservation
Porotergus duende is assessed by the IUCN Red List as Least Concern. It was described relatively recently, in 2010, and remains poorly studied, but its known range spans a substantial stretch of the western Amazon main channel across Brazil and Peru rather than being confined to a single small watercourse, which is consistent with a lower-risk assessment.
As with other main-channel Amazonian fish, the broader pressures facing the basin — damming, sediment and water-quality changes, deforestation and mercury contamination linked to mining — are relevant to its habitat even though no population-level threat has been documented for this species specifically. There is no evidence of trade-driven collection pressure, since the species is not a meaningful presence in the aquarium trade.