Taxonomy & naming
Gymnotus coropinae was described by Hoedeman in 1962 and belongs to the family Gymnotidae within the order Gymnotiformes, the New-World electric knifefishes. The order's defining feature is the electric organ discharge, or EOD — a weak electric field generated and carried around the body that the fish uses for electrolocation in dark or turbid water and for communication with others of its kind, each species and sex producing a characteristic signature discharge. Gymnotus is the pulse-type genus of the group: rather than emitting a continuous electric wave like the ghost knifefishes (Apteronotidae) or the glass knifefishes (Sternopygidae), Gymnotus fires discrete, separated pulses.
The species epithet coropinae refers to the type locality, Coropina Creek in Suriname, where the fish was first collected. It was redescribed in detail by Crampton & Albert in 2003, work that noted the species is frequently misidentified in older records because of confusion with other members of the Gymnotus carapo species complex — a group of superficially similar banded knifefishes that has since been split into 20 or more distinct species based on colour pattern, morphology and electric signal differences. The Catalog of Fishes is the authority for the valid name. Despite the shared common name "knifefish", Gymnotiformes are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the resemblance is convergent body shape, not kinship.
Morphology
Gymnotus coropinae has the classic banded-knifefish build: a stout, laterally compressed, blade-shaped body, dark brown overall and crossed by a striking series of pale white to yellowish bands — the FishBase account for the species records between eight and eighteen of them running down the flanks. As in all gymnotiforms there is no dorsal fin and no distinct tail fin; locomotion comes from a long anal fin running most of the length of the underside, thrown into travelling waves that let the fish move forwards or backwards with equal control. The species is scaleless.
It reaches a maximum recorded length of around 13.5 in standard length, with a maximum recorded weight of roughly 83.5 g — a solidly built, sturdy fish rather than a slender one. Running beneath the skin is the electric organ, and the surface of the body carries the sensory pores (electroreceptors) that pick up the field it generates. Electrophysiological work on the species has shown its electric organ discharge to be a genuinely complex, multi-component pulse — around 0.85 to 1.30 milliseconds long, combining a slower head-negative wave from the sub-opercular region with a fast, multi-phase spike from further down the body — timing that separates a near-field component useful for electrolocation from a far-field component useful for long-range communication.
Habitat
The species is broadly distributed across the Amazon and Orinoco basins and the Guyana Shield, a large stretch of tropical South America. It favours terra firme forest streams and swamps — blackwater and clearwater habitats typified by acidic pH and very low mineral content (low conductivity), often heavily shaded by forest canopy and stained by dissolved tannins from leaf litter.
That combination of darkness, structure and often oxygen-poor water suits a pulse-type electric fish well: where vision is nearly useless, an electric sense reads the surroundings just as effectively, and Gymnotus species are known to be facultative air-breathers, able to gulp air at the surface when dissolved oxygen in these swampy, still waters runs low. In the aquarium this points to a warm, dim, well-structured setup with soft, acidic water and plenty of cover such as roots, leaf litter and driftwood, rather than open, brightly lit swimming space.
Feeding
Gymnotus coropinae is a nocturnal predator, like the other banded knifefishes. It hunts after dark using electrolocation to find prey hidden in leaf litter, root tangles and soft substrate, feeding on aquatic invertebrates, small crustaceans and other small animals it can overpower — the genus as a whole is known for tough, opportunistic predatory habits rather than delicate picking.
In the aquarium, banded knifefishes of this kind take meaty foods readily — bloodworm, chopped earthworm, prawn and other frozen or live foods of appropriate size — and, as with other gymnotiforms, feed most actively once the lights are down. Given its predatory nature, any tankmate small enough to be swallowed should be assumed to be at risk after dark, regardless of how the fish behaves by day.
Mating
As in other Gymnotus, courtship and social interaction in G. coropinae are read out at least in part through the electric organ discharge. Because each individual's pulse carries species-, sex- and possibly individual-specific information, the electric field likely functions in this species as it does elsewhere in the genus and family — as a channel for recognising a potential mate or rival in the dark, alongside direct physical approach. Beyond this general pattern, courtship behaviour specific to G. coropinae is not well documented in the available literature; the cache for this species centres on its systematics, distribution and electric signal rather than on breeding behaviour.
Breeding
Reproduction has not been documented in detail for Gymnotus coropinae specifically, but the Gymnotidae are unusual among fishes for showing genuine parental care, and the pattern is well established in other Gymnotus species: the male builds and guards a nest — often a sheltered hollow among vegetation or a mass of floating material — the female spawns into it, and the male then guards the eggs and larvae, with spawning typically tied to seasonal flooding. There is no evidence to suggest G. coropinae departs from this genus-wide pattern, but breeding has not been reported from home aquaria for this species, and data remain sparse. Prospective breeders should treat any protocol as inference from the wider genus rather than a documented method for this species.
In the aquarium
Gymnotus coropinae is only occasionally available in the trade and suits an experienced keeper rather than a beginner. Being scaleless, it needs careful, mature water quality and reduced doses of copper-based or other harsh medications, which this group tolerates poorly. As a nocturnal predator it should be given a dimly lit tank with abundant cover — driftwood, root tangles and leaf litter suit both its habits and its wild habitat — and it is not community-safe with fish or invertebrates small enough to be eaten after dark.
Given its size, at up to roughly 13.5 in, and its solitary, often territorial temperament towards its own kind, it needs generous swimming space and is best kept singly or with only carefully chosen, robust tankmates too large to be prey. Because it can gulp air at the surface, it tolerates a wider range of dissolved-oxygen conditions than many aquarium fish, but this is not a reason to neglect filtration or water changes. Captive-bred stock is essentially unavailable for this species, so animals in the trade are wild-caught; buyers should weigh that against the fish's still-secure conservation status.
Conservation
Gymnotus coropinae is assessed as Least Concern on the IUCN Red List, an assessment dated 13 August 2020, reflecting its wide distribution across the Amazon and Orinoco basins and the Guyana Shield. It is not currently considered a species of conservation concern.
That said, the species relies on forest-stream and swamp habitats that are vulnerable to deforestation, water pollution and hydrological change across its range, pressures affecting many small-range Amazonian and Guianan fishes even where the individual species itself remains broadly distributed and is not yet threatened. As with other wide-ranging Neotropical fishes, its Least Concern status describes the picture across a continent, not the condition of any single stream system within it.