Taxonomy & naming
Pararcholaemus guchereauae was described by Meunier, Jégu & Keith in 2014, originally as Distocyclus guchereauae, based on holotype and paratype material from the upper Maroni basin in French Guiana. A 2025 taxonomic revision (published in Neotropical Ichthyology) erected the new genus Pararcholaemus for this species, making it the type species and separating it from Distocyclus. It belongs to the family Sternopygidae — the glass, rattail and open-water knifefishes — within the order Gymnotiformes, the New-World electric knifefishes.
Gymnotiformes are bony fish, but unusual ones: nearly every species produces a weak electric organ discharge (EOD) around its body, used for electrolocation in dark or turbid water and for communication with other knifefish. Sternopygidae, the family this species belongs to, are wave-type emitters — they produce a continuous, near-sinusoidal discharge rather than the intermittent pulses of some other gymnotiform families. The Asian featherback and clown knifefishes (Chitala, Notopterus) share the common name "knifefish" but belong to an entirely different order and are not related. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the current valid name and genus placement.
Morphology
As a member of Sternopygidae, Pararcholaemus guchereauae has the characteristic body plan of a glass or rattail knifefish: an elongated, laterally compressed body tapering to a slender tail, no dorsal fin, and a long anal fin running along most of the underside that undulates in travelling waves to drive the fish forward or backward with equal ease. FishBase records a maximum length of 13 in total length, a mid-sized species within the family. Like all gymnotiforms it is scaleless, which leaves the skin unusually exposed and has direct consequences for how sensitively the species must be treated with medications.
Running the length of the body is a myogenic (muscle-derived) electric organ, paired with sensory pores across the skin that read the field it produces — the sensing system that lets these fish navigate and hunt in water where eyesight is of limited use. Little has been published on external sexual dimorphism in this species; nothing in the available literature distinguishes males from females by appearance.
Habitat
This is a narrow-range endemic of the upper Maroni drainage, on the border between French Guiana and Suriname. It is known from the Litany, Paloemeu, Tampoc and Tapanahony rivers — all headwater tributaries of the Maroni system — with type material collected from sandbanks and backwaters adjacent to rapids in the upper Tapanahony. That habitat, fast-flowing rapids and the quieter water beside them, is similar to that reported for the related genus Archolaemus, and it fits the pattern seen across Sternopygidae of species favouring flowing river channels over still water.
No distribution outside the Maroni basin has been documented; this appears to be a single-basin endemic, one of many narrow-range gymnotiforms scattered across the smaller river systems of the Guiana Shield rather than the major Amazon or Orinoco channels.
Feeding
No species-specific dietary data has been published for Pararcholaemus guchereauae; the cache and available literature note this as an open gap. Based on the ecology of Sternopygidae generally, glass and rattail knifefishes are nocturnal micro-predators that hunt small invertebrates — aquatic insect larvae, worms and small crustaceans — locating prey in the dark largely through electrolocation rather than eyesight, working over the substrate and among cover after dark.
It would be an overstatement to assign this species a confirmed diet without direct study; what can be said with confidence is the family-level pattern of nocturnal, electrosensory micro-predation on small benthic invertebrates, and that any aquarium account of feeding this species would necessarily extrapolate from that pattern rather than from direct observation.
Mating
Nothing specific to Pararcholaemus guchereauae has been documented about courtship. In Sternopygidae generally, and especially in the well-studied glass knifefish genus Eigenmannia, the wave-type electric organ discharge is central to social and reproductive signalling: each fish's discharge frequency carries information about its identity and sex, rival males interact with distinctive electrical interference patterns, and courtship plays out partly as an exchange of electric signals in the dark alongside physical approach.
Whether P. guchereauae follows this same pattern in detail is not established in the literature — the species is data sparse on this point, and this account should be read as extrapolation from its family rather than direct observation of the species itself.
Breeding
Breeding biology has not been documented for this species specifically; it is rarely or never encountered in the aquarium trade, and no captive-spawning reports appear in the available sources. Sternopygidae as a family are egg-layers, typically scattering adhesive eggs among plant roots or floating vegetation in warm, soft, higher-water conditions associated with the wet season, with little to no parental care afterward — eggs are left among the vegetation rather than guarded.
Eigenmannia, the best-studied genus in the family, is bred in captivity more readily than most gymnotiforms, but that does not extend to this poorly known Maroni endemic. For Pararcholaemus guchereauae the honest summary is that reproduction is essentially undocumented, and any breeding attempt in captivity would be exploratory rather than following an established protocol.
In the aquarium
Pararcholaemus guchereauae is not an established aquarium fish; it is a narrow-range wild endemic with essentially no trade history, and this account draws on the general husbandry needs of Sternopygidae rather than on species-specific keeping reports. Like all scaleless gymnotiforms it would need great care with medications — no copper-based treatments, and reduced doses of anything else — plus consistently clean water, since scaleless knifefish are notably sensitive to ammonia and nitrate.
As a nocturnal predator adapted to dim, structured water it would need shaded retreats and subdued lighting, and — going by its 13 in adult size and its likely role as a micro-predator — it would not be safe with small or bite-size tankmates. In practice this is a species for specialist or research collections rather than the general hobby; if it is ever kept, captive-bred stock does not currently exist and any specimens would necessarily be wild-collected from an already narrow range.
Conservation
Pararcholaemus guchereauae is assessed by the IUCN as Near Threatened, reflecting its restriction to a small number of rivers within the upper Maroni basin straddling French Guiana and Suriname — a classic pattern among Guiana Shield gymnotiforms, where narrow-range single-basin endemics carry more conservation concern than the wide-ranging Amazonian and Orinoco species.
The pressures typical of this region include habitat change from mining and associated water pollution, and broader deforestation across the Maroni watershed; the assessment criteria cited by IUCN (restricted extent of occurrence and a small number of locations) point to sensitivity to any further habitat loss rather than to an already-observed population collapse. As with much of this species' biology, detailed threat data specific to P. guchereauae is limited, and the Near Threatened status should be read as reflecting its narrow range rather than a documented decline.