Taxonomy & naming
Mormyrus rume was described by the French ichthyologist Achille Valenciennes in 1847, with a type locality on the Senegal River in West Africa; the holotype, catalogued as MNHN A-9626, is held at the Muséum national d'Histoire naturelle in Paris. The Catalog of Fishes and GBIF both treat Mormyrus rume as the current, valid name for the species.
It belongs to the family Mormyridae, the elephant-snout fishes, within the order Osteoglossiformes — the bonytongues, one of the oldest living lineages of teleost fish. Bonytongues are a deep-time radiation scattered across four continents, and the group found in Africa (Mormyridae, plus a handful of other families) is not closely related to the arowanas of South America and Asia or the featherback knifefishes, despite some superficial resemblance. The genus Mormyrus is one of the largest in the family, with dozens of described species spread across African rivers and lakes, many separable with confidence only by the waveform of their electric-organ discharge rather than by outward appearance.
The genus name comes from the ancient Greek mormyros, originally the name of an unrelated marine sea bream and later carried over by early naturalists to this freshwater African group. The origin of the species name rume is not well documented in the sources consulted here; it does not correspond to an obvious Latin or Greek root and may derive from a local vernacular name recorded at the type locality.
Morphology
Mormyrus rume has the elongated body typical of its genus, with a long-based dorsal fin set toward the rear of the body, a short anal fin, and a tubular, somewhat elongated snout ending in a small, terminal mouth. That combination of a long dorsal fin, short anal fin and tubular snout is a useful field mark separating Mormyrus from other mormyrid genera, such as the short-snouted Gnathonemus with its mobile chin appendage.
FishBase records a maximum length of around 39.4 in, which puts Mormyrus rume among the largest species in its genus and far beyond the small elephantnose species — Gnathonemus petersii and similar — that dominate the aquarium trade at 7.9–9.8 in.
As in all mormyrids, an electric organ near the base of the tail produces a weak, species-specific, pulse-type electric-organ discharge. A related genus has been measured discharging around 25 volts when a fish is netted or stressed. The fish reads distortions in this self-generated field through electroreceptors covering its skin, a sense used to detect obstacles, prey and other fish in dark or turbid water where vision is of limited use. Mormyrids as a family are noted for some of the highest brain-to-body-mass ratios of any fish, with an enlarged cerebellum devoted to processing this constant stream of electrosensory information.
Habitat
Mormyrus rume has one of the broadest distributions of any mormyrid, recorded from the Senegal, Gambia, Niger, Volta and Chad basins in West Africa, from a cluster of smaller coastal rivers further south and east — the Bandama, Sassandra, Komoé, Mono, Ouémé, Ogun and Culufi — and from the Congo basin in Central Africa. Few African mormyrids span this many independent river systems; most Mormyrus species are confined to a single basin.
It is a demersal, potamodromous fish, living and feeding near the bottom and moving within fresh water rather than migrating to sea, typically tracking the seasonal rise and fall of its home rivers and their floodplains. Species-specific temperature and pH readings are not documented in the sources reviewed here; the general pattern across its West African and Congo basin range is soft, often turbid or tannin-tinted water in the main channels and floodplain margins, the low-visibility conditions the electric sense evolved to read.
Feeding
Mormyrus rume is a presumed nocturnal invertebrate forager, in keeping with the pattern documented across its genus: it is thought to sweep its tubular snout through soft bottom sediment for aquatic insect larvae, worms and small crustaceans, using its weak electric field to locate prey it cannot see. Species-specific feeding data for this fish is not documented in the sources consulted here.
General care guidance for elephant-snout fishes in the aquarium describes a diet built around live and frozen foods — bloodworm in particular — with sinking carnivore pellets accepted once a fish has settled in; prepared flake food is usually ignored. Feeding after dark, to match the family's natural activity pattern, tends to get a better response than daytime feeding.
Mating
Courtship in mormyrids is understood to run through the electric-organ discharge: subtle differences in pulse waveform and pattern are thought to let fish recognise species, sex and individual identity, and to figure in courtship and dominance interactions. Beyond that general picture, the mating behaviour of Mormyrus rume specifically has not been documented in the sources available here.
In the wild, mormyrids are generally understood to be seasonal spawners tied to flood cycles, spawning when rising water opens up floodplain habitat and food. No aquarium account of courtship or spawning in this species is documented, and sexes cannot be reliably told apart by external appearance.
Breeding
Breeding of Mormyrus rume in captivity is, as far as the sources reviewed here indicate, essentially unrecorded, and mormyrid breeding in general is poorly understood and only rarely achieved outside the wild. The species' large adult size compounds the usual difficulties of keeping and pairing mormyrids in an aquarium setting.
Some mormyrids are thought, from field observation, to scatter eggs among flooded vegetation with little or no subsequent parental care, but this has not been confirmed for Mormyrus rume. Anyone who encounters a claimed captive breeding of this species should treat it as a notable, poorly documented event rather than a repeatable method.
In the aquarium
Size is the first thing to plan around: FishBase's reported maximum of roughly 39.4 in makes Mormyrus rume one of the largest mormyrids anyone is likely to encounter, a different proposition entirely from the small elephantnose species usually recommended to newcomers. A tank sized for a 7.9 in Gnathonemus petersii is nowhere near adequate for an adult of this species, and it should be acquired only with a large, mature, long-term setup already in place.
Mormyrids as a family are consistently described as sensitive to water quality — sensitive enough that some species have been used as bioindicators in municipal water testing — and this species should be assumed to share that sensitivity until shown otherwise. Stable, well-filtered, soft to moderately hard water on the acidic-to-neutral side, dim lighting, a soft substrate for foraging, and secure cover such as driftwood and root tangles suit a fish that is most active after dark and relies on electrolocation rather than sight.
Elephant-snout fishes are usually described as peaceful toward unrelated tankmates but intolerant of their own kind in small numbers, with two or three individuals prone to persistent aggression as a dominance hierarchy fails to settle; care guidance for the family generally recommends either a single specimen or a larger group with room to disperse. Given this species' size, either option means a substantial, dedicated aquarium rather than an addition to a general community tank.
Conservation
The IUCN Red List assesses Mormyrus rume as Least Concern, an assessment dated 4 June 2019. Its documented range across many independent river systems — from the Senegal and Gambia basins through the Niger, Volta and Chad basins to the Congo — supports that status: this is not a species confined to a single threatened river or lake the way many African freshwater fish are.
A wide range does not mean every population within it is secure, and West African rivers face pressures from damming, sedimentation, pollution and overfishing in places. No sources reviewed here document a species-wide population decline, and Mormyrus rume is not currently considered threatened.