Taxonomy & naming
Steatogenys duidae was described by Francesca La Monte in 1929, originally placed in the now-defunct genus Tateichthys as Tateichthys duidae before being moved into Steatogenys. It belongs to the family Rhamphichthyidae, the sand knifefishes, within the order Gymnotiformes — the New-World electric knifefishes, a group defined not by scales or fins but by an electric organ and a ribbon-like anal fin that does almost all the work of swimming. The Catalog of Fishes (Eschmeyer, CAS) is the authority for the valid name.
The species epithet duidae refers to the type locality, Mount Duida in Amazonas state, Venezuela; the genus name Steatogenys derives from Greek steat- (fat, tallow) and -genys (jaw), a reference to the fish's soft, fleshy head profile. Despite the shared common name "knifefish", Steatogenys and its Gymnotiform relatives are not related to the Asian featherback and clown knifefishes (Chitala, Notopterus) — those belong to an entirely separate order of bonytongues, and the resemblance in body shape is convergent, not a sign of kinship.
Morphology
The centipede knifefish is long and slender, tapering from a bluntly rounded snout to a whip-thin tail, with a barred or mottled brown pattern that camouflages it well among leaf litter and submerged wood. As in all Gymnotiformes it has no dorsal fin and no true tail fin; a single long anal fin runs beneath most of the body and drives the fish with a travelling ripple, letting it move forward, hover, or reverse with equal control. The species reaches a modest maximum of around 8 in total length, small by the standards of the larger ghost and banded knifefishes.
Like every fish in this order it is entirely scaleless, its skin bare and covered instead with the sensory pores of its electroreceptive system. It carries a weak, pulse-type electric organ that fires discrete individual pulses — as opposed to the continuous wave-type discharge of the ghost knifefishes (Apteronotidae) — a pattern typical of the Rhamphichthyidae and its close relatives the Hypopomidae. No sexual dimorphism has been documented for this species; males and females are not reliably distinguished by external features in the available literature.
Habitat
Steatogenys duidae is native to the Amazon and Orinoco basins, recorded from Brazil and Venezuela, with a range that plausibly extends into neighbouring Colombia and Peru given the connectivity of the basin. The type locality sits on Mount Duida in Venezuela's Amazonas state, and specimens have also been documented from Igarapé Tabocão, a tributary of Lago Aiapuá in Brazil, giving a picture of a fish tied to terra firme forest streams — watercourses that run through unflooded forest rather than seasonally inundated várzea.
These are warm, soft, acidic waters typical of the Amazon's blackwater and clearwater tributaries, with moderate current and a substrate of sand, leaf litter and submerged roots. The species is nocturnal and spends daylight hours hidden among this cover, emerging after dark — behaviour consistent with its weak electric sense, which lets it navigate and hunt in water where vision offers little advantage. In the aquarium it wants that same dim, sheltered, softwater environment recreated as closely as possible.
Feeding
In the wild the centipede knifefish is a carnivore, taking small crustaceans, worms and aquatic insect larvae from among the leaf litter and sediment it patrols at night, almost certainly locating much of this prey by electrolocation rather than sight. It forages actively rather than ambushing, working through cover in the manner typical of small nocturnal Rhamphichthyids.
In the aquarium it accepts bloodworm, ghost shrimp and similar meaty frozen or live foods, and consistently rejects commercial flakes and pellets — feeding has to be built around live or frozen fare offered after the lights go down. Because it is shy and easily outcompeted, food is best delivered where the fish can find it without having to compete in the open with bolder tankmates.
Mating
As in other Gymnotiformes, the electric organ discharge of Steatogenys duidae likely does double duty as a communication channel as well as a sensing tool — pulse-type signatures in this order can carry information about species, sex and individual identity, and are thought to feature in how individuals recognise and approach one another in the dark. Beyond that general pattern, specific courtship behaviour for this species has not been documented in the available sources.
Data on the finer detail of pairing and spawning approach in S. duidae is sparse; what is known is inferred from its family rather than observed directly in this species. It is best treated as an open question rather than a settled account.
Breeding
Breeding in Steatogenys duidae is poorly documented, both in the wild and in the aquarium — no confirmed captive spawning records appear in the available literature. As an egg-layer in the family Rhamphichthyidae, its reproduction is presumed to follow the pattern typical of its relatives: eggs scattered or deposited among leaf litter, roots or sand, likely timed to the wet season, with little to no parental care afterward.
This is a species to keep well rather than to expect to breed. Aquarists should treat any reproduction as a documentation opportunity rather than a routine outcome, and resist the temptation to fill gaps in the record with assumption.
In the aquarium
The centipede knifefish suits a quiet, softwater biotope tank rather than a boisterous community. It is peaceful but shy, and does best kept in a group of six or more of its own kind — solitary individuals are prone to becoming stressed or, conversely, unusually aggressive toward tankmates. A soft, sandy substrate with plenty of leaf litter, roots and other cover lets it hide through the day and emerge to forage at night, and dim lighting suits its nocturnal habits far better than a brightly lit display.
Being scaleless, it needs the same caution given to all Gymnotiformes: no copper-based medications, reduced dosing of anything else, and consistently clean water, since it is sensitive to ammonia and nitrate. Warm water in the 73–82 °F range with a soft, acidic pH of around 6.0–6.5 mirrors its terra firme forest streams. It is not a fish for bite-size community tankmates — small fish and shrimp are at risk from a nocturnal electrolocating predator — but it poses no threat to similarly sized peaceful companions. Captive-bred stock is not established in the trade for this species, so wild-caught origin should be assumed and the fish given time and cover to settle in.
Conservation
Steatogenys duidae has not been formally assessed by the IUCN Red List and carries a status of Not Evaluated. It is known from a modest number of Amazon and Orinoco basin localities in Brazil and Venezuela, in terra firme forest streams that are not, on current evidence, under acute documented pressure specific to this species.
As with many small, poorly studied Neotropical fishes, the absence of an assessment reflects a lack of dedicated study rather than any known security. General pressures on Amazon and Orinoco forest streams — deforestation, water quality change and habitat disturbance — are relevant to the wider region this species inhabits, but no species-specific conservation data is available to cite.