Taxonomy & naming
Gymnotus pantanal was formally described in 2005 by Fernandes, Albert, Daniel-Silva, Lopes, Crampton and Almeida-Toledo, part of a wave of description work that has split the old, broadly defined Gymnotus carapo into a large number of narrower, better-defined species. It belongs to the family Gymnotidae within the order Gymnotiformes, the New-World electric knifefishes — bony fish, but very unusual ones, defined by an electric organ running the length of the body and a single long anal fin that does almost all the swimming. The genus name Gymnotus comes from the Greek gymnos, 'naked', and notos, 'back', a reference to the absent dorsal fin shared across the order.
The species epithet pantanal refers directly to its type locality, the Pantanal Matogrossense of Brazil — the world's largest tropical wetland — rather than to a Latin or Greek root. Gymnotus is the only genus in the order Gymnotiformes that reaches Central America, extending north through the Amazon and Orinoco basins all the way to southern Mexico, while the rest of the New-World electric knifefishes (ghost knifefishes, glass knifefishes, sand knifefishes) are confined to South America. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name. Despite the shared common name, Gymnotus and its relatives are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus); the knife-like body shape is convergent, not a sign of kinship.
Morphology
Gymnotus pantanal has the classic banded-knifefish build: a stout, laterally compressed, scaleless body marked with thin, obliquely angled pale bands with wavy margins across the front half of the ventral flank, set against a darker ground colour — a pattern that helps distinguish it from the several other Gymnotus species it lives alongside in the Pantanal, including G. inaequilabiatus and G. sylvius. As in all Gymnotiformes there is no dorsal fin and no proper tail fin; propulsion comes from a long ribbon-like anal fin running most of the length of the underside, which the fish undulates to move forward or backward with equal ease.
Maximum recorded size is around 10 in total length. Running beneath the skin along the body is the electric organ that generates the species' pulse-type discharge, paired with electroreceptor pores scattered over the head and body that read the resulting field. Gymnotus pantanal is also a facultative air-breather, able to gulp air at the water's surface when dissolved oxygen runs low — a useful adaptation for the stagnant backwaters and seasonally shrinking pools of its floodplain habitat.
Habitat
The species is known from the Pantanal Matogrossense of Brazil and adjacent drainages, including the upper Paraguay and Paraná river systems and the Chapare–Mamoré river of Bolivia — a range centred on one of the largest tropical wetlands on Earth, spanning Brazil, Paraguay and Bolivia. Within that floodplain it is found in small creeks and larger backwater rivers, characteristically among rooted grasses and floating aquatic macrophytes rather than open channel.
The Pantanal is a strongly seasonal system, flooding extensively in the wet season and contracting to disconnected pools and sluggish creeks in the dry season, with regional air temperatures ranging from roughly 68–79 °F on a monthly average and extremes well beyond that. Water in these vegetated backwaters is often warm, soft to moderately mineralised and low in dissolved oxygen, conditions the species' air-breathing habit and generally tough constitution are well suited to. As in other Gymnotus, dim, turbid or vegetation-shaded water suits the fish's electric sense far better than clear, brightly lit water.
Feeding
Gymnotus pantanal is a nocturnal predator, and FishBase lists it at a trophic level of roughly 3.3 — a mid-level carnivore rather than a top predator. Like other banded knifefishes it hunts by night among submerged vegetation and debris, using its electric sense to locate aquatic invertebrates, insect larvae and small fish hidden in cover or buried in sediment, where eyesight in the dark, silty water of the Pantanal would be of little use.
Specific dietary data for this species is sparse beyond its trophic-level placement, but Gymnotus as a genus are opportunistic, active nocturnal hunters rather than passive ambush feeders, and in the aquarium they take a wide range of meaty foods. In the wild the dense floating and rooted vegetation of its habitat likely also shelters much of its prey base.
Mating
As in other Gymnotiformes, electricity is woven into courtship: the pulse-type electric organ discharge that G. pantanal uses to navigate and hunt also carries information about species identity and, very likely, sex and reproductive state, and courtship and rival encounters in Gymnotus are understood to involve exchanges and shifts in this electric signalling alongside physical approach in the dark. The finer detail of courtship behaviour specific to G. pantanal has not been documented; much of what is known about electric courtship in the genus comes from related, better-studied Gymnotus species rather than from this one directly.
Reproduction in the Pantanal is tied to the flood pulse: Gymnotus species there are understood to spawn seasonally as rising water floods the grass beds and creates the sheltered, food-rich nursery habitat their young need, though the precise seasonal triggers for G. pantanal itself are not well documented in the available literature.
Breeding
Gymnotidae are unusual among fishes in showing real parental care, and in Gymnotus generally the male builds and guards a nest — often a mass of floating vegetation, foam or a sheltered hollow among roots and grass — into which the female spawns; the male then guards the eggs and, subsequently, the larvae. This pattern is documented for the genus as a whole, but breeding has not been specifically recorded for Gymnotus pantanal, whether in the wild or in captivity, and no aquarium spawnings of this species appear to be documented.
Given how recently the species was described (2005) and how little-known it remains outside its type region, the honest position is that its breeding biology is inferred from its close relatives rather than observed directly. It should not be expected to spawn in a home aquarium, and no reliable breeding protocol exists for it.
In the aquarium
Gymnotus pantanal is essentially unknown as an aquarium fish; there is no meaningful hobby history to draw on, and it should be treated as an occasional, specialist import rather than a fish to plan a stocking list around. What can be said comes from its genus: Gymnotus are hardy, adaptable, air-breathing predators that tolerate a wide range of water conditions far better than many gymnotiforms, but they are nocturnal hunters and not remotely community-safe with anything small enough to swallow, including similarly sized tankmates in some cases — they are often territorial with their own kind, too, and are usually best kept singly or with ample space and cover to divide territory.
Being scaleless, it needs the same caution around medications as its relatives: no copper-based treatments, and reduced doses of anything else, alongside clean, well-filtered water, since scaleless fish are unusually sensitive to ammonia and nitrate. A dim tank with dense planting or floating cover, sand or fine substrate, and secure hiding places would replicate the vegetated floodplain creeks it comes from. Any specimen in the trade should be treated as wild-caught, since no captive-breeding program for this species is documented.
Conservation
Gymnotus pantanal is assessed by the IUCN as Least Concern, reflecting a range that spans a substantial part of the upper Paraguay–Paraná system across Brazil, Paraguay and Bolivia rather than a single isolated locality. It is not currently considered at elevated risk of extinction.
That said, its core range sits within the Pantanal, a floodplain ecosystem under mounting pressure from deforestation in its headwaters, agricultural expansion, altered fire regimes and hydrological changes linked to upstream dams and land-use change across the wider Upper Paraguay basin. Species tied closely to seasonally flooded grass-and-macrophyte habitat, as G. pantanal is, are vulnerable to any disruption of the natural flood pulse even where the species itself is not yet flagged as threatened, and its status is worth revisiting as pressure on the Pantanal continues to build.