Taxonomy & naming
Marcusenius verheyenorum was described in 2020 by Mambo Baba, Kisekelwa, Mizani, Decru and Vreven as part of a study revealing hidden species diversity within what had long been treated as a single wide-ranging species, Marcusenius moorii. Using mitochondrial DNA (cytochrome b) together with a re-examination of external morphology, the authors showed that populations from the upstream middle Congo Basin were genetically and morphologically distinct from true M. moorii, and split them off as a new species. It belongs to the family Mormyridae — the elephantnoses and mormyrids — within the order Osteoglossiformes, the bonytongues, a scattered, deep-time radiation of freshwater fishes found today across South America, Africa, Southeast Asia and Australasia. The order's name and shared "bonytongue" character refer to a toothed bone on the floor of the mouth that bites against toothed plates on the roof of the mouth, an ancient feeding mechanism found across this otherwise very diverse group.
The genus name Marcusenius honours the naturalist Marcusen, commemorated in a number of mid-19th-century mormyrid names. The species epithet verheyenorum is a Latinised plural genitive patronym — the "-orum" ending honours more than one person sharing the surname Verheyen, in keeping with the common ichthyological convention of naming a new species after researchers who contributed to the work; the specific individuals honoured are not confirmed in the sources consulted here. Interestingly, two specimens collected from the Lilanda River back in the 1950s and long filed away as M. moorii turned out, on re-examination, to belong to this newly recognised species — and because no further specimens have turned up there since, M. verheyenorum is thought to be locally extinct at that particular site even as it persists elsewhere in its range.
Morphology
Marcusenius verheyenorum has the compact, deep-bodied build typical of its genus: a rounded head with a small, terminal mouth (rather than the elongated, trunk-like "schnauzenorgan" chin appendage seen in some other mormyrids, such as Gnathonemus petersii), a short, deep caudal peduncle, and a body proportioned more heavily than many of its Marcusenius relatives. Meristic counts recorded in the original description include 38–43 lateral-line scales, 40–41 vertebrae, 20–21 dorsal-fin rays and 26 anal-fin rays — the kind of fine-grained scale and fin-ray counts that, alongside genetics, are what actually separate this species from its close relatives rather than any single obvious external field mark.
As in all mormyrids, the tail carries a weak electric organ — an electrocyte-packed structure in the caudal peduncle — that generates a brief, species-typical pulse discharge. This is paired with an unusually large cerebellum and an electrosensory lateral-line lobe, giving mormyrids one of the highest brain-to-body-mass ratios of any fish group, the physiological basis for their reputation as unusually "intelligent" fish (really a reflection of processing a rich electrosensory world rather than general problem-solving). Maximum length has not been established for this species in the sources available; based on the typical range for the genus it is likely a modest-sized elephantnose, but this should be read as an estimate rather than a confirmed figure — data sparse.
Habitat
Marcusenius verheyenorum is currently known only from right-bank tributaries of the upper-middle Congo River in the Democratic Republic of the Congo, with records from within and around the Yangambi Biosphere Reserve and the Okapi Wildlife Reserve. That narrow, tributary-scale distribution — plus the apparent local disappearance from the Lilanda River site where it was first (if unknowingly) collected in the 1950s — marks this as a Congo-basin endemic known from a comparatively small area rather than a widespread river-system species.
Like other Congo-basin mormyrids, it almost certainly lives in warm, generally soft, tannin-stained forest-tributary water rather than open, brightly lit river channel — exactly the kind of low-visibility habitat in which an electric sense is most useful for finding food and other fish in the dark. No species-specific water-chemistry measurements were located in the sources consulted; this account follows the general pattern documented for the wider genus rather than site-specific readings for M. verheyenorum itself.
Feeding
No feeding study specific to Marcusenius verheyenorum was located in the sources consulted, so this account extrapolates from the wider genus. Like other Marcusenius, it is presumed to be a bottom-foraging invertebrate feeder, using its electric sense to probe soft substrate and cover for aquatic insect larvae, small crustaceans and other invertebrates, most likely under cover of darkness or in the naturally dim light of its Congo-basin tributary habitat.
Because the species is not established in the aquarium trade, there is no aquarium feeding record to draw on either. Aquarists working with related Marcusenius species have found that mormyrids generally take live or frozen invertebrate foods — bloodworm, brine shrimp and similar aquatic insect larvae — far more readily than dry foods, and that offering food after the lights dim tends to suit their natural rhythm better than daytime feeding, but none of this has been confirmed for verheyenorum specifically.
Mating
Courtship and mate recognition in mormyrids run through the electric organ discharge: each species' pulse pattern is thought to help fish recognise their own kind and, within a species, to signal readiness or status between individuals — a communication channel layered on top of the same electrolocation sense used for foraging. Whether that holds true in the specific detail for Marcusenius verheyenorum has not been documented; as a species described only in 2020 from a small number of preserved and field-collected specimens, its courtship behaviour in the wild has simply not been studied.
What can reasonably be inferred from the wider mormyrid family is a pattern of seasonal, flood-triggered spawning tied to the rise and fall of Congo-basin rivers, rather than fixed pairing or year-round breeding. Detailed observations of courtship displays, pairing behaviour or spawning sites for this species do not exist in the literature available — this is a case of "data sparse" rather than a known account.
Breeding
Breeding is essentially unresolved for this species and has, as far as the available sources indicate, never been achieved or documented in captivity — unsurprising for a mormyrid described this recently and never established in the aquarium trade. Wild mormyrids in general are understood to be seasonal spawners cued by flooding, and some genera are thought to scatter eggs among submerged plants or roots with little to no active parental care, but none of that has been confirmed specifically for Marcusenius verheyenorum.
There is no captive-breeding protocol to offer here, and none should be assumed or improvised from related species. This account deliberately stops short of describing a breeding method for M. verheyenorum: the honest position is that its reproductive biology is poorly known, full stop.
In the aquarium
Marcusenius verheyenorum is not a species anyone should expect to find in the hobby: it is known from only a handful of Congo-basin tributary localities, was described only in 2020, and there is no record of it being kept or bred in captivity. Nothing in this account should be read as an invitation to seek out wild-collected specimens of a species this poorly documented.
What can be said follows from the broader genus and family. Mormyrids in general need soft, dimly lit, stable water with plenty of cover — bright lighting is documented to cause wasting and stress in elephantnoses generally — and, being scaleless like all mormyrids, they are markedly more sensitive than scaled fish to salt, copper and many standard medications. Any of these general Mormyridae care points would apply if this species were ever to appear in the trade, but none of it has been tested against M. verheyenorum specifically, and its narrow known range argues strongly against collection pressure rather than for it.
Conservation
Marcusenius verheyenorum has no IUCN Red List assessment: it is Not Evaluated, most plausibly because the species was described only in 2020 and has not yet been through a formal Red List review. Congeners such as M. moorii, M. macrolepidotus and M. angolensis are typically assessed Least Concern or Data Deficient, but that pattern cannot simply be assumed for this species given how narrow its currently known range is.
The known distribution — a small number of right-bank Congo tributaries in and around the Yangambi Biosphere Reserve and the Okapi Wildlife Reserve — is more restricted than that of most of its relatives, and the species' apparent disappearance from the Lilanda River, where it was collected in the 1950s but has not been found since, is a genuine cause for caution even without a formal threat assessment. Both reserves offer some measure of habitat protection, but broader Congo-basin pressures — deforestation, sedimentation and localised habitat disturbance — are the kind of threats that would matter for a narrow-range endemic like this one. A formal IUCN assessment specific to M. verheyenorum would be the natural next step.