Taxonomy & naming
Mormyrops attenuatus was described by the Belgian-British ichthyologist George Albert Boulenger in 1898, with a type locality at Upoto on the upper Congo River. It belongs to the family Mormyridae — the elephantfishes and mormyrids — a strictly African family of roughly 200 species and one of two families (alongside the monotypic Gymnarchidae) making up the order Osteoglossiformes, the bonytongues. Osteoglossiformes is among the oldest living lineages of teleost fish, its members named for a bony, toothed structure on the tongue that bites against a toothed plate on the roof of the mouth; the order's living representatives are scattered across South America, Africa, Southeast Asia and Australasia, a deep-time relict of a once more widespread radiation. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Mormyrops attenuatus as a valid species.
The genus name Mormyrops combines Mormyrus — the name of a related mormyrid genus, itself derived from an old Greek name for a fish — with the Greek suffix -ops, "face" or "appearance", so the genus name reads roughly as "Mormyrus-like". The species epithet attenuatus is Latin for "thinned" or "tapered", describing the elongate, gradually narrowing body that helps separate Mormyrops from the deeper-bodied or chin-appendaged mormyrids in neighbouring genera such as Gnathonemus.
Morphology
Mormyrops attenuatus is a modestly sized mormyrid, reaching about 8.7 in total length (FishBase) — a fraction of the size some of its Mormyrops relatives attain, and within the range that makes for a manageable, if unusual, aquarium fish. As the name suggests, the body is elongate and tapers gradually toward the tail, with a long-based dorsal fin (39–41 rays) set well back on the body and an even longer anal fin (59–61 rays) running much of the ventral length — a fin arrangement typical of mormyrids, in which the dorsal and anal fins beat in a slow, sculling wave that lets the fish hover, reverse and hold station with precision.
Like all mormyrids, M. attenuatus carries a weakly electric organ in the caudal peduncle, near the base of the tail, which fires a continuous train of brief electrical pulses. A dense field of electroreceptors covers the body and reads the distortions this field makes as it passes over rocks, plants, prey and other fish — an active sixth sense that substitutes for vision in the dark, often turbid Congo basin water where mormyrids do most of their foraging. The genus Mormyrops is defined in part by a comparatively small, terminal mouth without the elongated, flexible chin barbel (the schnauzenorgan) that gives genera such as Gnathonemus their trunk-like profile; the head instead tapers into the slender body without a distinct proboscis. Coloration in life is a fairly plain grey to brownish tone, typical of Congo basin mormyrids adapted to dim, tannin-stained water rather than to visual display.
Habitat
Mormyrops attenuatus is known from the middle Congo River basin, with records spanning Cameroon, the Democratic Republic of the Congo and Angola; its type locality is Upoto, on the upper Congo River. Like most of its family it is demersal, living close to the riverbed of the main channel and larger tributaries rather than in open water, over sand, mud and submerged debris where it can forage and shelter by day.
The middle Congo basin is warm, tropical freshwater and — as for Congo-basin mormyrids generally — typically soft and only lightly mineralised, running from slightly acidic to near neutral and often stained the tea-brown of dissolved plant tannins. Visibility in these waters is often poor, which is precisely the environment the mormyrid electric sense evolved to read: where eyes struggle, the electric organ discharge does not. Beyond this broad basin-level picture, detailed population or micro-habitat data for this particular species is sparse.
Feeding
In the wild, Mormyrops attenuatus almost certainly forages the way other mormyrids do: nocturnally, using its electric organ discharge to electrolocate prey hidden in sediment or debris rather than hunting by sight. The diet is presumed to be the standard mormyrid fare of aquatic invertebrates — insect larvae, worms and small crustaceans — picked from the substrate after dark, though no detailed dietary study of this species specifically was found in the sources consulted here.
In the aquarium it should be treated as a nocturnal, benthic feeder. Sinking foods offered after the lights go out — frozen bloodworm and blackworm, chopped prawn or shrimp, and quality sinking pellets — suit it well. Because it forages slowly, by touch and electric sense rather than by sight, it can lose out to faster, more visually driven tankmates at feeding time, and is best fed on its own or in a species-only tank.
Mating
Mating behaviour in Mormyrops attenuatus has not been documented in detail, and being honest about that gap matters more than filling it in. What is known comes from the wider mormyrid literature: in the wild, mormyrids are generally seasonal spawners whose reproduction is tied to the rains and the flooding of river margins, and the electric organ discharge — beyond its role in foraging — is thought to double as a courtship and species-recognition signal, letting a fish distinguish a potential mate of its own species from the many other electric fish sharing the same water.
Beyond that broad pattern, the courtship and pairing behaviour of this species is essentially unknown. Aquarium sources are consistent on one point: breeding in Mormyridae as a family is very rarely achieved in captivity, and the great majority of specimens reaching the hobby are wild-caught rather than tank-bred.
Breeding
No aquarium breeding of Mormyrops attenuatus has been documented in the sources reviewed here, and captive breeding of mormyrids in general is described as very difficult and only patchily understood — a handful of species have spawned under controlled conditions, but the process is not something a home aquarist can reliably reproduce. Some mormyrids are thought to scatter eggs among plants or fine root mats in flooded margins with no organised nest and little parental care beyond that, but the specifics for this species have not been studied.
Given this, the honest position for a keeper is that Mormyrops attenuatus should be regarded as effectively unbred in captivity: expect wild-caught stock, expect no breeding project to succeed without a great deal of luck and a very large, stable system, and treat any claim of routine home-tank spawning with real scepticism.
In the aquarium
Mormyrops attenuatus is a specialist's fish, not a casual community addition. Sources are consistent in placing it in soft, only lightly mineralised water — reported ranges span roughly pH 6.0–7.5 and 72–84 °F, with soft water in the region of 5–12 dGH — kept in a tank that is dimly lit, well furnished with plants, driftwood and caves, and above all quiet during the day: this is a nocturnal fish that is most active once the lights go down. It reaches around 8.7 in (roughly 6–9 in in aquarium accounts), so while it does not carry the size trap of the true giants of this order, it still wants a properly sized tank with soft substrate to forage over and hiding places to retreat to.
Two care points follow directly from its biology. First, the electroreceptive skin of mormyrids generally makes them more sensitive than average to poor water quality and to some medications — dose gently, avoid copper-based treatments where possible, and keep the tank stable rather than reaching for aggressive dosing. Second, mormyrids can be territorial or intolerant of their own kind in a confined tank; a single specimen, or a genuinely large system that lets individuals establish separate space, tends to work better than a crowded group. Nearly all specimens in the trade are wild-caught, so patient acclimation and quarantine deserve extra attention.
Conservation
The IUCN Red List assesses Mormyrops attenuatus as Least Concern, an assessment dated 16 February 2009. It is known from a reasonably broad span of the middle Congo basin across Cameroon, the Democratic Republic of the Congo and Angola, and nothing in the available sources points to a specific, elevated threat to the species as a whole.
That said, a 2009 assessment is now well over a decade old, and the Congo basin faces ongoing pressure from habitat degradation, sedimentation and the general expansion of fishing and development along its river systems. Because nearly all aquarium specimens are wild-caught rather than captive-bred, collection for the trade is a minor but real draw on wild populations, even if it is not currently flagged as a conservation concern at the assessment level.