Taxonomy & naming
Marcusenius meronai was described by the ichthyologists Robert Bigorne and Didier Paugy in 1990, with its type material collected from Sierra Leone. It belongs to the family Mormyridae, within the order Osteoglossiformes, the bonytongues: a scattered, deep-time radiation of fishes found on four continents — South America, Africa, Southeast Asia and Australasia — united not by any shared modern habitat but by that toothed lingual bone, and numbered among the most ancient lineages of living teleosts. The Mormyridae are an exclusively African family, every member weakly electric, and entirely convergent with — not related to — the electric knifefishes of South America (order Gymnotiformes), which evolved an equivalent electric sense independently on the opposite side of the Atlantic.
The species epithet meronai honours the French ichthyologist Dr Bernard de Mérona. Marcusenius is one of the largest genera in the Mormyridae, and as in many of its relatives, species-level identification here is difficult from preserved specimens alone: fin-ray counts and other subtle meristic characters separate close relatives on paper, but confident field identification in this genus typically rests on the fish's electric organ discharge (EOD) rather than on external appearance.
Morphology
Marcusenius meronai shows the general mormyrid build: a laterally compressed, elongate body, a small, close-set mouth, and a caudal peduncle housing the tail-mounted electric organ that defines the family. FishBase records 21–23 dorsal fin rays and 25–29 anal fin rays for the species, and a maximum size of about 7.4 in standard length — a small-to-mid-sized mormyrid, well short of the metre-plus giants found elsewhere in the family, and modest even by the standards of the smaller West African Marcusenius.
Detailed published description of colouration and fin proportion beyond those meristic counts is thin in the sources available here. As in other mormyrids, an outsized cerebellum drives one of the highest brain-to-body ratios recorded in any vertebrate, the physiological cost of running a sensitive electrolocation and communication system built around that tail organ; this is a family-wide trait rather than something specifically studied in this species.
Habitat
Marcusenius meronai is known only from the Bagbé and Rokel Rivers in Sierra Leone, making it a narrow West African endemic restricted to a single small country rather than a wide-ranging river system shared across borders. This tight distribution — rather than any documented population crash — is the main driver of its conservation status (see "Conservation").
Mormyrids of West African coastal rivers are typically fish of turbid, sediment-laden and often tannin-stained water — sluggish stretches with submerged wood, leaf litter and low visibility, exactly the setting in which an electric sense outperforms eyesight. Species-specific temperature and pH figures for Marcusenius meronai were not available in the sources consulted here; the water is presumed to follow the warm, generally soft-to-moderate tropical West African river conditions typical of the family, and this article does not invent precise figures beyond that. FishBase notes only that the species needs stable, clean water and is sensitive to poor conditions.
Feeding
No species-specific feeding study for Marcusenius meronai was located in the sources consulted here, but its biology is presumed to follow the general mormyrid pattern: a largely nocturnal, electrolocation-guided forager that sweeps soft substrate for small aquatic invertebrates — worm and insect-larva prey hidden in mud, sand or leaf litter — using its weak electric organ discharge to detect food in water too dim or turbid for vision to be reliable.
Mormyrids in general have small, weak dentition and are poor competitors for dry or floating foods; in the aquarium, related species are usually kept on live and frozen invertebrates — mosquito larvae, bloodworm, Tubifex, Daphnia and Cyclops — which they take far more readily than prepared foods. This pattern is noted here as a reasonable expectation for the genus rather than a confirmed fact for this exact species.
Mating
Courtship and mate recognition in mormyrids are believed to run substantially through the electric organ discharge rather than through visual display — the pulse itself may encode species identity, sex and readiness to spawn — but this has not been specifically documented for Marcusenius meronai. Across the family, wild spawning is thought to be seasonal, cued by the rains and rising floodwater of the West African wet season.
The electrical and acoustic noise of a home aquarium — filters, heaters, pumps, reflective glass — readily interferes with the weak EOD signal mormyrids rely on for this kind of communication, one reason natural courtship essentially never plays out under aquarium conditions for fish in this family.
Breeding
Marcusenius meronai is, so far as the sources consulted here record, not bred in the aquarium hobby — no captive spawning has been documented — and, as with most mormyrids, its reproductive biology in the wild is poorly understood. Breeding is presumed to be seasonal and flood-triggered, and some mormyrids are thought to guard eggs among vegetation, but no such detail has been confirmed for this species. Size at sexual maturity is also unrecorded.
Aquarists should not expect or attempt to breed this fish. Given its documented rarity and restricted range (see "Conservation"), any specimens in the trade would be wild-caught, and there is no established captive-breeding protocol to fall back on.
In the aquarium
At under 7.9 in, Marcusenius meronai is a manageable size for a mormyrid, but general family guidance still applies: a tank of at least 39.4 in in length, soft substrate, dim lighting and ample cover — roots, wood and plant thickets — to feel secure, with most activity after dark. It is a scaleless, electrosensitive fish and, like other mormyrids, notably sensitive to poor water quality and to many aquarium medications, copper-based and formalin treatments in particular; dosing should be approached with real caution and stable water quality is a genuine requirement rather than a nicety.
Mormyrids can also be intolerant of their own kind and of other electric fish sharing a confined space, and some keepers house them singly to avoid electrical interference between individuals. Given how narrow this species' known range is and how little has been published on it in the aquarium literature, prospective keepers should treat any specimen as a genuinely uncommon fish rather than a routine import, and prioritise stable, calm, low-noise conditions over an active community setup.
Conservation
The IUCN Red List assesses Marcusenius meronai as Endangered, an assessment dated 2019 under criterion B1ab(iii) — a listing driven by an extent of occurrence estimated to be small and a continuing decline in the quality of its habitat, rather than by any single catastrophic event.
The species is known only from the Bagbé and Rokel river systems in Sierra Leone, a genuinely narrow range for a freshwater fish, which leaves it with little buffer against localised habitat degradation — sedimentation, deforestation of riparian cover, and water-quality decline are the general pressures affecting Sierra Leone's coastal rivers, though the sources consulted here do not detail threats specific to this species beyond the range-restriction that underpins its Red List criterion.