Taxonomy & naming
Electrophorus varii belongs to the family Gymnotidae within the order Gymnotiformes, the New-World electric knifefishes — an assemblage of scaleless, electricity-generating fish found only in Central and South America and entirely unrelated to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus). Its closest relatives within Gymnotidae are the banded knifefishes of the genus Gymnotus, but Electrophorus stands apart as the order's one strongly electric lineage, capable of discharges powerful enough to stun prey and deter predators, rather than the weak, sensing-only discharges typical of the rest of the order.
For over two centuries the genus was treated as a single species, Electrophorus electricus, described by Linnaeus in 1766. That changed in 2019, when de Santana and colleagues, working from genetic, morphological and bioelectric data, split the genus into three species: E. electricus, restricted to the northern Guiana Shield; E. voltai, from the southern Brazilian Shield uplands and the source of the record-setting 860-volt discharge; and E. varii, described from the central Amazon lowlands. The species is named for the American ichthyologist Richard Peter Vari (1949–2016), a Smithsonian curator whose work on Neotropical fishes underpins much of the taxonomy this split relied on. The Catalog of Fishes is the authority for the valid name.
Morphology
Electrophorus varii has the unmistakable body plan of the electric eel: a long, cylindrical, scaleless form with no dorsal fin and no proper tail fin, propulsion instead coming from an extremely long anal fin that runs almost the entire length of the underside and lets the fish move forward or backward with equal control. Adults reach roughly 1.5 metres in total length in examined specimens, making this — like its two sister species — one of the largest gymnotiforms known, and a serious commitment for any facility housing one.
Described as having a comparatively thick skull and cleithrum (shoulder-girdle bone) and a more variable head shape than its sister species, E. varii can be distinguished from E. electricus and E. voltai mainly through combined genetic, morphological and bioelectric evidence rather than a single obvious external field mark. Along its flanks run the paired electric organs that dominate the body cavity — in Electrophorus these occupy the great majority of the trunk, leaving comparatively little space for other internal organs. Reported discharge voltages for the species range from roughly 151 volts in smaller individuals (around 8 in total length) up to about 572 volts in larger fish (around 24 in), with a brief high-voltage pulse duration on the order of 1.2 to 1.8 milliseconds — a wave-type low-voltage discharge is used continuously for electrolocation, while distinct high-voltage pulses are unleashed to stun prey or deter threats.
Habitat
Electrophorus varii is confined to the lowland floodplain and terra-firme (non-flooded forest) waters of the intercratonic central Amazon Basin, quite distinct from the upland Guiana Shield range of E. electricus and the upland Brazilian Shield range of E. voltai. Its type locality is the Goiapi River on Marajó Island at the mouth of the Amazon in Pará, Brazil, and it is generally reported from shallow, slow-moving lowland waters with dense vegetation, submerged branches and leaf litter offering cover.
These floodplain habitats are frequently and severely hypoxic — dissolved oxygen can fall below 0.5 mg/l in the stagnant, tannin-stained backwaters the species favours, conditions that would exclude most fish outright. Electrophorus survives there because it is an obligate air-breather: it must surface every few minutes to gulp air through its heavily vascularised mouth lining, extracting the bulk of its oxygen this way rather than through its reduced gills. That adaptation is what lets it colonise warm, still, low-oxygen backwaters that few other predators can use, but it also means the fish drowns if it cannot reach the surface — a critical point for anyone housing one.
Feeding
Electrophorus varii is a nocturnal, opportunistic predator that relies on its unique combination of electrolocation and a stunning electric discharge to hunt in dark, turbid, vegetation-choked water where vision is of limited use. Low-voltage, wave-type discharges are used continuously to sense the surroundings and locate prey by the way it distorts the fish's electric field, while sudden high-voltage pulses are used to immobilise prey outright before it is engulfed — a hunting method essentially unique among freshwater fish.
Diet across the genus centres on fish, together with invertebrates and, for the largest individuals, small vertebrates encountered in the water; E. varii's own diet has not been closely documented, but it is reasonable to expect the same broadly piscivorous, opportunistic pattern seen in its better-studied relatives. In captivity — which for this species means public aquaria and research collections rather than home tanks — electric eels are typically fed whole fish, and any facility keeping one must plan for a genuinely large predator's appetite and the safety implications of housing a fish capable of a powerful electric discharge.
Mating
As in other gymnotiforms, courtship in Electrophorus is thought to be mediated in part by electric organ discharge — the wave-type signal each individual produces likely carries information relevant to species and sex recognition and readiness to spawn, layered on top of its primary role in electrolocation. Detailed courtship behaviour has not been documented for E. varii specifically, and much of what is inferred for the genus is extrapolated from the far better-studied Gymnotus and from the handful of captive breeding events recorded for E. electricus.
What is documented for the genus points to a seasonal, dry-season spawning pattern timed to the Amazon's flood pulse, with reproduction concentrated in the period when floodplain waters recede and conditions in sheltered shallows become suitable for nest-building. Data specific to E. varii's mating behaviour is sparse, and this account should be read as extrapolated from genus-level knowledge rather than species-specific observation.
Breeding
Electrophorus is one of the few gymnotiform genera with documented parental care. In the dry season, males construct a foam nest from saliva in a sheltered shallow-water site along a riverbank or floodplain margin; the female deposits a large clutch — reported in the low thousands of eggs for the genus — into the nest, and the male then guards the eggs and the resulting shoal of larvae until conditions change with the return of the rains. Breeding has been documented for E. electricus essentially only in dry-season, flood-pulse-timed events, and almost never outside large, carefully managed public-aquarium or research settings.
No breeding-specific data exists for E. varii in the sources reviewed here, and given how rarely any Electrophorus species has been bred under human care, it should be treated as effectively unbred outside its wild range. The practical reality for this species is that captive reproduction is not a realistic goal for anyone but a specialist research or public-aquarium program with the space, water volume and safety infrastructure the fish demands.
In the aquarium
Electrophorus varii is not a home aquarium fish, and any account that suggests otherwise is doing readers a disservice. This is a scaleless, obligate air-breathing predator that reaches roughly a metre and a half in length and is capable of delivering a genuinely dangerous electric shock — a public-aquarium and specialist research animal only, requiring an enormous volume of water, constant access to the surface to breathe, and stringent safety protocols around anyone working near the tank.
Where it is kept, in institutional settings, the requirements follow directly from its biology: warm, soft, tannin-stained water reflecting its Amazon floodplain origin; the ability to reach the surface unimpeded at all times, since it will drown if prevented from air-breathing; dim lighting and cover consistent with its nocturnal habits; and, because it is scaleless, careful attention to water quality and extreme caution with medications, particularly copper-based treatments, which are poorly tolerated by knifefishes generally. No responsible keeper should attempt to house this species outside an institutional context.
Conservation
Species-specific IUCN Red List assessment data for Electrophorus varii was not found in the sources reviewed for this article; the genus Electrophorus is broadly regarded as Least Concern, reflecting a wide collective range across the Amazon and Guiana Shield region and no evidence of significant population decline, but that genus-level picture should not be read as a confirmed, dedicated assessment of this individual species.
The central Amazon lowlands E. varii inhabits face real and growing pressure from deforestation, water pollution and habitat alteration tied to agricultural expansion and development across the basin. As with many recently split, range-restricted Neotropical fishes, a formal species-level assessment specific to E. varii would help clarify whether its narrower, lowland-restricted range carries conservation concerns distinct from its more widely distributed relatives.