Taxonomy & naming
Mormyrus ehrenbergii was described by the French zoologist Achille Valenciennes in 1847. It belongs to the family Mormyridae within the order Osteoglossiformes, the bonytongues — a name that refers to a toothed bone on the floor of the mouth that bites against toothed plates on the roof, a structure found across this ancient, scattered lineage of freshwater fishes on four continents. The genus Mormyrus is one of the largest genera of mormyrids, with roughly sixty recognized African species, most sharing an elongated body and a downturned, often elongated snout.
Catalog of Fishes treats Mormyrus longirostris as a junior synonym folded into Mormyrus ehrenbergii, which is why some older literature and the common name "eastern bottlenose mormyrid" attach to this species. As with many mormyrids, species boundaries in the genus have shifted repeatedly as ichthyologists have re-examined museum material and, more recently, the fish's own electric-organ discharge, which is often a more reliable species marker than external appearance.
Morphology
Mormyrus ehrenbergii has the elongated, laterally compressed body typical of its genus, with a small, ventrally set mouth on a moderately produced, downcurved snout — the "bottlenose" shape that gives the species its common name. The dorsal fin sits far back on the body, roughly opposite a long-based anal fin; FishBase records 65 to 75 soft dorsal rays and 17 to 19 soft anal rays, both fins noticeably elongated compared with most other freshwater fish families. The caudal fin is small and forked, and at its base sits the electric organ, a modified muscle tissue that generates the fish's weak electric-organ discharge (EOD).
Colouration is a plain silvery to grey-brown, without the bold pattern many aquarium mormyrids show. Reported maximum size is about 29.5 in total length and 10 kg, making this one of the larger species in the genus — well beyond the elephantnose (Gnathonemus petersii) familiar to aquarists. Like other mormyrids, Mormyrus ehrenbergii has an unusually large cerebellum relative to its body size, among the highest brain-to-body-mass ratios recorded in any fish, an adaptation linked to processing the constant stream of electrosensory information its EOD provides.
Habitat
Mormyrus ehrenbergii is an East African freshwater fish, recorded from the Zambezi basin — including the Zambezi, Buzi, Pungwe, Sabi and Ludi rivers — the Luapula–Mweru–Bangweulu system, and the Ruvuma and Rufiji rivers of Tanzania, as well as Lakes Malawi, Tanganyika and Rukwa. That spread places it across Malawi, Mozambique, Tanzania, Zambia, Zimbabwe and the Democratic Republic of the Congo. It is a demersal, bottom-associated fish and potamodromous, meaning it makes seasonal movements entirely within fresh water, typically timed to river floods rather than to the sea.
Across this range it occupies slower, often turbid or sediment-stained river and floodplain water and the shallower margins of the lakes it inhabits — the low-visibility conditions in which a weak electric sense is more useful than vision. Water chemistry specific to Mormyrus ehrenbergii populations is not well documented in the sources available; it is best treated as a warm, stable, East African river and lake fish rather than assigned to any one narrow set of parameters.
Feeding
As a demersal mormyrid, Mormyrus ehrenbergii almost certainly feeds on benthic invertebrates — insect larvae, worms and similar prey probed out of sand and sediment — in the manner documented for its better-studied relatives. Mormyrids generally have small eyes and rely on electrolocation rather than sight to find food buried in the substrate, sweeping the electric field generated by their tail organ over the bottom to detect prey by the tiny distortions it causes.
Species-specific feeding data for Mormyrus ehrenbergii is sparse. Aquarium care notes compiled for Mormyridae generally recommend live and frozen invertebrate foods — bloodworm, mosquito larvae, Daphnia, Tubifex and brine shrimp — for mormyrids kept in captivity, and there is no reason to expect this species to differ, but no observation specific to it is available here.
Mating
Mormyrids use their electric-organ discharge for more than navigation: the pulse pattern is species-specific and is thought to play a role in courtship and mate recognition, letting fish identify potential partners of the right species in murky water where visual cues are limited. The details of that signalling in Mormyrus ehrenbergii specifically have not been documented in the sources reviewed here.
The species is potamodromous, and like many African floodplain fish its reproductive movements are likely tied to seasonal flooding, when rising water opens up flooded vegetation and marginal habitat. Beyond that general pattern shared across the genus, the courtship behaviour of Mormyrus ehrenbergii is not well described in the literature.
Breeding
Breeding in Mormyrus ehrenbergii is poorly known, and this species is essentially not bred in aquaria. Across the mormyrids as a group, wild spawning is understood to be seasonal and flood-triggered, and there is some suggestion that parents may guard eggs laid among aquatic plants, but hard evidence at the species level is thin and not established for Mormyrus ehrenbergii in particular.
Captive breeding of mormyrids of any kind is rarely if ever achieved outside research settings, and this species — far too large for the display aquaria in which smaller mormyrids are occasionally kept — has essentially no aquarium breeding record. Anything more specific than "seasonal, flood-associated spawning" would be guesswork rather than documented fact.
In the aquarium
Mormyrus ehrenbergii is not a realistic aquarium fish. A species that reaches roughly 29.5 in and 10 kg in the wild belongs in the same size category as the large arowanas and the arapaima — a public-aquarium or research-institution animal, not a home tank, and it is not established in the ornamental trade for that reason.
The general husbandry lessons that do apply come from the wider Mormyridae, and they are worth knowing for anyone keeping smaller relatives such as the elephantnose (Gnathonemus petersii): dim lighting and ample cover over a soft sand or fine gravel substrate that will not abrade a foraging snout, stable and clean water with low turbidity, a temperature in the roughly 75–82 °F range, and slightly acidic to neutral pH. Mormyrids are notably intolerant of copper, formalin, dyes and salt, all of which can be lethal at doses other fish tolerate, and they can be aggressive toward their own kind in confined space. None of this changes the basic fact for Mormyrus ehrenbergii: its adult size puts it out of reach of aquarium keeping.
Conservation
No species-specific IUCN Red List assessment was found for Mormyrus ehrenbergii; the species has effectively not been formally evaluated (Not Evaluated / Data Deficient), a status shared by many East African mormyrids that have never been the subject of a dedicated conservation review despite fairly wide distributions.
Its range across several major basins and lakes — the Zambezi system, the Congo-linked Luapula–Mweru–Bangweulu waters, the Rufiji and Ruvuma rivers, and Lakes Malawi, Tanganyika and Rukwa — suggests no single acute threat is known to endanger the species as a whole, but the absence of an assessment means no formal conservation status exists to confirm that. General pressures on East African freshwater systems, including damming, sedimentation and fishing pressure on larger-bodied species, are the plausible long-term concerns for a fish of this size and habitat, though none has been documented specifically for Mormyrus ehrenbergii.