Taxonomy & naming
Mormyrus macupe was described by the German naturalist Wilhelm Peters in 1855, based on specimens collected during his mid-19th-century survey of Mozambique and the lower Zambezi region. It belongs to the family Mormyridae, the elephantnose fishes and mormyrids, within the order Osteoglossiformes, one of the oldest surviving branches of teleost (bony) fish, a group whose name comes from a toothed bone at the back of the tongue that bites against toothed plates on the roof of the mouth.
The Catalog of Fishes and FishBase both treat Mormyrus macupe as a junior synonym of Mormyrus longirostris, a name Peters had already published three years earlier, in 1852, from the same general region. Under current taxonomy the fish once called M. macupe is simply M. longirostris, a single species now recognized across the lower Zambezi and its tributaries (the Buzi, Pungwe, lower Sabi and Ludi rivers), the Luapula-Moero-Bangweulu system that connects toward the upper Congo, the Ruvuma and Rufiji rivers of Tanzania, and lakes Malawi, Tanganyika and Rukwa. This account follows that identity and uses macupe as a historical name for the same fish.
Mormyrus is a large genus, with roughly 22 recognized species of long-snouted African elephantnose fishes distributed from West Africa to the Nile and south to the Zambezi. Many are difficult to separate from one another by appearance alone, and ichthyologists increasingly rely on the fish's own species-specific electric organ discharge, alongside fin-ray counts and snout proportions, to confirm identifications.
Morphology
Mormyrus longirostris has the long, tapering, downward-curving snout that gives the genus its common names of bottlenose or elephant-snout fishes, a fleshy extension of the jaws rather than the separate, trunk-like chin barbel (schnauzenorgan) found in the unrelated genus Gnathonemus. The body is elongate and laterally compressed, with a small mouth set well back on the underside of the snout, a single soft dorsal fin positioned opposite a similarly sized anal fin, and a small forked tail on a slender caudal peduncle.
FishBase records a maximum size of about 29.5 in and a published weight up to 10 kg, making this one of the larger species in the genus; fish of that size are old adults, and any juveniles reaching the aquarium trade are far smaller. Coloration is a plain silvery-grey to brownish-olive, without the bold pattern seen in many aquarium fish; like most Mormyrus, it is not a species identified on looks alone.
As in all Mormyridae, an electric organ built from modified muscle cells (electrocytes) sits in the caudal peduncle near the base of the tail. It produces a continuous, low-voltage, species-specific pulse discharge that the fish reads with electroreceptors spread across its skin, building a real-time electrical picture of its surroundings. Processing that signal demands unusual amounts of neural tissue: mormyrids carry one of the highest brain-to-body-mass ratios of any fish, with an enlarged, elaborately folded cerebellum, a feature that has earned the family a reputation among aquarists and neuroscientists as unusually capable "thinking fish."
Habitat
Mormyrus longirostris (as M. macupe) is native to south-central and East African fresh waters: the lower Zambezi River and its tributaries the Buzi, Pungwe, lower Sabi (Save) and Ludi; the Luapula-Moero-Bangweulu system draining toward the upper Congo; the Ruvuma and Rufiji rivers of Tanzania; and lakes Malawi, Tanganyika and Rukwa. It is a freshwater, bottom-associated (demersal) fish recorded across Zambia, Mozambique and Tanzania.
The species is potamodromous, making seasonal migrations within fresh water between main river channels and adjoining floodplains as water levels rise and fall with the rains. Typical mormyrid habitat of this kind is warm (roughly 75–82 °F), soft and only mildly acidic to neutral (about pH 6-7), and often turbid or tannin-stained, the low-visibility conditions in which a weak electric sense outperforms eyesight.
Feeding
Mormyrus longirostris feeds on benthic invertebrates: aquatic insect larvae, small crustaceans and worms taken from the river or lake bed. The long snout sweeps and probes soft substrate, and, as in other mormyrids, electrolocation lets the fish detect buried or hidden prey well before it comes into view, an advantage in the dim, sediment-heavy water it favors.
Foraging activity in the genus is typically concentrated around dusk and after dark, when many mormyrids are most active; aquarium accounts of related species likewise report the fish becoming markedly more active once the lights go down.
Mating
Wild reproduction in Mormyrus, as in Mormyridae generally, is a seasonal, flood-triggered event: spawning is thought to follow the rise of water levels and the flooding of marginal vegetation, which likely provides both cover and food for young fish. Species-specific detail on courtship in M. longirostris has not been established.
The electric organ discharge is known to play a role in courtship and species recognition across the family: a fish can in principle identify a compatible mate of the right species by its EOD waveform before any visual contact. Exactly how that translates into pairing and spawning behavior for this species is undocumented. It is one of many mormyrids whose reproductive biology is simply poorly known outside a handful of well-studied genera.
Breeding
Mormyrus longirostris (M. macupe) has essentially never been bred in captivity, and published accounts of its reproduction are minimal even in the wild. What is known follows the general mormyrid pattern: spawning tied to seasonal floods, with eggs presumably laid among flooded marginal vegetation, though direct observation for this species is lacking.
Parental care, if any, is poorly understood; some mormyrids are thought to guard eggs briefly among plants, but this has not been confirmed for M. longirostris specifically. This is not a species anyone should expect to breed at home. Its reproductive biology remains one of the open questions in mormyrid natural history, and its large adult size puts sustained captive breeding further out of reach regardless.
In the aquarium
The headline problem with keeping this fish is size: a species that reaches roughly 29.5 in and up to 10 kg is not a home-aquarium animal in any realistic sense. Small individuals occasionally reach the trade under the elephant-snout or Mormyrus longirostris name, but buyers should assume steady growth toward a fish that needs a tank measured in meters, not a spot in a standard community setup. This is a large, public-aquarium-scale fish rather than a tankmate for a mixed African community.
For the smaller Mormyrus species that are genuinely aquarium-appropriate, and for any young M. longirostris kept temporarily, the general mormyrid care rules apply: soft sand or fine-mud substrate (never sharp gravel, which can injure the sensitive snout as the fish forages), dim lighting, and a tank at least 59.1 in long even for modest-sized species. Live and frozen foods, mosquito larvae, bloodworm, white worms, black worms, daphnia, tubifex and cyclops, are strongly preferred over dry foods.
Mormyrids are notoriously sensitive to poor water quality and to many medications, so stable, clean water and cautious, conservative dosing matter if treatment is ever needed. They are also not reliably peaceful toward their own kind: keep them singly or in a properly conditioned group rather than an unstable pair, and watch for aggression when territories are contested. None of this changes the core point for this particular fish: its adult size rules it out of virtually every home setup.
Conservation
No species-specific IUCN Red List assessment exists for Mormyrus macupe or for its accepted name, Mormyrus longirostris; the status is Not Evaluated. Related congeners that have been assessed, including Mormyrus niloticus and Mormyrus caschive, carry a Least Concern rating, hinting at a genus-wide pattern of low conservation concern, but that is not itself an assessment of this species.
The known range spans multiple major river systems and three African Great Lakes, which argues against any single, well-defined threat at present. As with many African freshwater fish, the longer-term pressures worth watching are habitat degradation, damming and altered flood regimes on the rivers it depends on for its floodplain-linked life cycle, and general overfishing pressure on lake and river fisheries, but specific population data for this species are not available.