Taxonomy & naming
Brachyhypopomus hendersoni was described by Crampton, de Santana, Waddell & Lovejoy in 2016 (published 2017) as one of fifteen species treated together in a major revision of the genus Brachyhypopomus. It belongs to the family Hypopomidae, the bluntnose knifefishes, within the order Gymnotiformes — the New-World electric knifefishes, a bony but electrically unusual group defined by their electric organs and a single long ribbon-like anal fin used for propulsion in place of the usual fin arrangement.
The species epithet honors Peter A. Henderson (b. 1954), a British fish biologist and Amazonian aquatic ecologist. The type specimen (MCP 45489, a female of 6.5 in total length) came from the Amazon basin. As with all Gymnotiformes, B. hendersoni is not related to the superficially similar Asian featherback and clown knifefishes (Chitala, Notopterus) despite sharing the common name "knifefish" — the resemblance is convergent body shape, not kinship. The Catalog of Fishes is the authority for the valid name.
Morphology
Like other bluntnose knifefishes, Brachyhypopomus hendersoni has a soft, cryptically pigmented body and a short, rounded (bluntnose) head rather than the elongated snout seen in the related sand knifefishes. It lacks a dorsal fin and a true tail fin; movement comes from an elongated anal fin running most of the length of the underside, undulated to drive the fish forward or backward with equal facility. Females can reach about 8 in total length and males about 7.5 in, with an anal-fin ray count in the range of 192–210 — one of the traits used to separate Brachyhypopomus species from one another.
The defining biology, shared with its relatives, is a weak electric organ running down the body and an array of sensory pores across the skin that read the electric field it generates. In Brachyhypopomus this discharge is pulse-type — short, discrete pulses on the order of 0.5–5 milliseconds rather than a continuous wave — used for electrolocation in the dark and for signalling identity, sex and status to other knifefish. The species is scaleless, a trait that carries directly into how sensitive it is to water quality and medication.
Habitat
Brachyhypopomus hendersoni is known from the central Amazon and lower Rio Negro in Brazil and the Essequibo drainage in Guyana — nutrient-poor blackwater habitat typical of much of the Amazon basin. Recorded conditions are warm (around 84–91 °F) and acidic to soft (pH roughly 5.3–6.7), in slow-flowing or still, tannin-stained water.
As a bluntnose knifefish it is a benthopelagic, nocturnal, cryptically pigmented predator, likely sheltering by day among leaf litter, roots and submerged vegetation in the manner typical of the family, and becoming active after dark when its electric sense takes over from vision in the near-opaque blackwater. This is exactly the kind of dim, structurally complex, slow-flowing water the family favors across its range from southern Costa Rica to southern Uruguay.
Feeding
Direct dietary data for Brachyhypopomus hendersoni specifically is sparse, but the genus and family are consistent: bluntnose knifefishes are nocturnal predators of small aquatic invertebrates, primarily aquatic insect larvae — chironomid (midge) larvae feature heavily in related species' diets — along with other small benthic invertebrates. Prey is located mostly by electrolocation rather than sight, in keeping with the dim, turbid blackwater the species inhabits.
As a small, delicate fish with no aquarium-trade history to draw on, there is no established feeding regimen to report; any care would need to extrapolate from the family's known preference for live and frozen invertebrate foods (bloodworm, small crustaceans) offered after dark.
Mating
Courtship and spawning behaviour in Brachyhypopomus hendersoni have not been directly documented; what is known is inferred from the genus and the family. As in other Gymnotiformes, the pulse-type electric organ discharge is understood to carry information about species, sex and reproductive condition, and is likely used in signalling between prospective mates in the dark, alongside physical approach — but no field or captive observation of courtship in this species has been published.
Reported reproduction in the wider genus Brachyhypopomus centres on seasonal spawning associated with rising or high water, with eggs deposited among floating or submerged macrophytes rather than in a nest or burrow. Whether B. hendersoni follows this same seasonal pattern in the central Amazon and Essequibo is plausible by extension but not separately confirmed.
Breeding
Breeding biology for Brachyhypopomus hendersoni is poorly documented and there is no record of the species being bred in captivity; it has essentially no aquarium-trade presence. What data exists for the genus points to seasonal egg-scattering among floating and submerged macrophytes during rising-to-high water, with little or no parental care afterward — the general Hypopomidae/Rhamphichthyidae pattern of small, short-lived, prolific egg-layers rather than mouthbrooders or nest-guarders.
Given how recently the species was described (2016/2017) and the near-total absence of hobby interest, the honest position is that breeding mode is inferred from relatives rather than observed directly in this species, and any aquarist attempting it would be working from the family's general pattern rather than a species-specific protocol.
In the aquarium
Brachyhypopomus hendersoni is not an established aquarium fish; it is a recently described, scientifically documented species with no meaningful hobby history, and this account should be read as inference from its family rather than as tested husbandry advice. Any keeper attempting it should expect to work largely from first principles drawn from the bluntnose and sand knifefishes as a group.
Those general principles matter here: like all Gymnotiformes it is scaleless and will be sensitive to ammonia, nitrate, and to copper-based or harsh medications, which should be avoided or used at reduced dose. It is a nocturnal, electrolocating predator that will want dim lighting, soft acidic blackwater conditions in the 84–91 °F range reported from its native habitat, plenty of fine cover (leaf litter, roots, dense planting) to retreat into by day, and tankmates too large to be treated as prey — small fish and shrimp are not safe with any electric knifefish after dark. Given the total lack of trade history, captive-bred stock does not exist, and any specimen encountered would almost certainly be wild-collected.
Conservation
Brachyhypopomus hendersoni is assessed as Least Concern on the IUCN Red List, an assessment dated December 2022, with no documented narrow-range endemic threats. Its known range spans multiple blackwater systems — the central Amazon and lower Rio Negro in Brazil and the Essequibo drainage in Guyana — rather than a single isolated river, which likely supports the low-concern status even though it is a recently described and still poorly surveyed species.
As with many small, cryptic Gymnotiformes, the practical caveat is that a Least Concern rating reflects limited but adequate distribution data rather than active monitoring; the general pressures facing Amazonian blackwater habitats — deforestation, mining-related pollution and mercury contamination, and hydrological change from damming — remain relevant to the wider region even where no species-specific decline has been recorded.