Taxonomy & naming
Brevimyrus niger was described by the German-British ichthyologist Albert Günther in 1866. It sits in 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) and united by that toothed lingual bone rather than by any shared modern habitat. The Mormyridae themselves are an exclusively African family of several hundred species, all weakly electric, and entirely convergent with — not related to — the electric knifefishes of South America (Gymnotiformes); the two groups evolved similar electric senses independently on opposite sides of the Atlantic.
Brevimyrus is a monotypic genus: Brevimyrus niger is its only species. The genus name is conventionally read as a contraction of Latin brevis, "short", and Mormyrus, the family's type genus, together suggesting "short mormyrus" — a nod to the compact, deep-bodied build that sets it apart from more elongate relatives. The species epithet niger is Latin for "black", describing the fish's dark, near-blackish colouring. As with most mormyrids, close relatives can look very similar to the naked eye and are reliably told apart only by their species-specific electric organ discharge (EOD), so field and aquarium identifications based on appearance alone deserve appropriate caution.
Morphology
Brevimyrus niger is a small mormyrid, reaching a reported maximum of about 5.9 in total length and reaching sexual maturity at roughly 4.3 in. The body is compressed and deep-bodied for the family, in a dark, near-black to charcoal colouring that matches the species name. Unlike the trunk-snouted elephantnoses of genus Gnathonemus, Brevimyrus has no elongated Schnauzenorgan; the head is blunt and rounded, a profile that — together with the dark body — is almost certainly what earned imported fish the aquarium trade nicknames "baby whale" and "baby dolphin".
As in other mormyrids, an electric organ near the base of the tail generates a weak, pulse-type electric organ discharge (EOD) used for electrolocation and communication in dark or turbid water, and the family is known generally for an outsized cerebellum and a very high brain-to-body ratio — the physiological cost of running a sensitive electrosensory system in place of relying on vision.
Habitat
Brevimyrus niger is widespread across a broad swath of West and Central African freshwater, with records from the Senegal, Gambia, Niger, Volta and Ouémé river basins, the Chad basin, and the White Nile — a distribution ichthyologists group together as the Sahelo-Sudanese basins, a huge belt of savanna-zone rivers running from Senegal in the west to the Nile in the east. It is a benthopelagic fish of vegetation-rich floodplain areas rather than open river channel, living among flooded grasses and submerged structure where the water is shallow, still and often turbid.
Reported conditions are warm and markedly soft and acidic: FishBase records a temperature around 72–75 °F and a pH near 5.0, consistent with the dim, sediment- and vegetation-influenced floodplain water typical of this fish's range — precisely the kind of low-visibility habitat in which an electric sense outperforms eyesight. Given how wide the basin list runs, local conditions likely vary somewhat from one floodplain to the next; treat these figures as representative rather than universal.
Feeding
Like other mormyrids, Brevimyrus niger is believed to be a nocturnal forager that uses active electrolocation from its tail's electric organ to detect aquatic invertebrates — insect larvae, worms and small crustaceans — hidden in soft substrate and among flooded vegetation, hunting confidently after dark or in turbid water where sight is of little use.
In the aquarium it does well on a bloodworm- and Tubifex-based diet, offered over a soft sandy substrate that suits natural foraging behaviour; sharp gravel should be avoided, as it can injure a foraging mormyrid. Feeding after lights-out, matching the fish's nocturnal rhythm, tends to get the best results.
Mating
Wild reproductive behaviour in Brevimyrus niger is not well documented, but the species is recorded as a seasonal floodplain spawner, breeding in step with the rains and rising water that define the West African wet season — a pattern typical of Sahelo-Sudanese river fishes generally. As in other mormyrids, courtship and mate or species recognition are thought to run substantially through the electric organ discharge rather than through visual display, though the specific signal characteristics involved in this species have not been described in the literature.
A mormyrid's electrosensory communication is easily disrupted by the electrical and acoustic noise of a home aquarium — filters, heaters, pumps and glass-tank reflections all interfere with a weak EOD signal — which is one reason natural courtship essentially never plays out in captivity for fish in this family.
Breeding
Brevimyrus niger is essentially not bred in the aquarium hobby, and like most mormyrids its reproductive biology is poorly known even in the scientific literature. It is recorded as a seasonal, flood-triggered floodplain spawner reaching maturity at around 4.3 in, but the details of courtship, spawning site, egg-laying and any parental behaviour have not been reliably documented for this species.
Aquarists should not expect to breed this fish. Specimens in the trade are wild-caught, generally imported from Nigeria, and the species is best approached as a fish to keep and observe rather than a project fish to pair for eggs.
In the aquarium
Brevimyrus niger is a small mormyrid by family standards, but it still asks for a properly sized, mature aquarium: aquarium-care sources recommend a tank of 75 US gallons (roughly 74 US gal) or more, with soft sandy substrate, dim lighting and stable water chemistry. Sudden temperature swings are a real risk — a change of more than about 10 °F (41–43 °F) can be fatal — so a reliable heater and thermometer matter more here than in most community setups, while the heater itself (like powerheads and other electrical equipment) should be positioned away from where the fish forages, since electrical noise can interfere with its EOD-based navigation and feeding.
As in other mormyrids, water quality needs to stay excellent and stable, and this is a fish that tends to be sensitive to medications, so any dosing calls for caution. Mormyrids can also be territorial toward their own kind, sparring over space and their individual electric "signature"; boisterous or fin-nipping tankmates should be avoided, and calm, non-aggressive companions that won't out-compete a nocturnal forager for food after dark are the better match.
Conservation
The IUCN Red List assessed Brevimyrus niger as Least Concern in 2019. The species' wide distribution across the Senegal, Gambia, Niger, Volta, Ouémé, Chad and White Nile basins — spanning a large stretch of Sahelo-Sudanese West and Central Africa — supports that assessment; it is not currently considered at risk at the species level.
As with many broadly distributed African floodplain fishes, the main long-term pressures are generic rather than species-specific: wetland drainage, dam construction that disrupts natural flood cycles, and general habitat degradation across the savanna-zone rivers it inhabits. There is no evidence in the available sources of a population decline driving reassessment, and the picture for this widespread, adaptable mormyrid remains reassuring for now.