Taxonomy & naming
Mormyrus subundulatus was described by the American ichthyologist Tyson R. Roberts in 1989. 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, named for a toothed bone on the floor of the mouth that bites against a matching pad on the roof. The Catalog of Fishes treats Mormyrus subundulatus as the current valid name.
The species is one of a cluster of similar-looking Mormyrus from West African rivers, and for years it was difficult to separate reliably from two close relatives, M. tapirus and M. rume, on external appearance alone. A morphological and DNA study of specimens from the Bandama River confirmed it as a distinct, valid species, distinguished from its look-alikes by fin-ray counts — 60 to 71 soft rays in the long-based dorsal fin and 16 to 18 in the anal fin — alongside genetic differences. The genus name Mormyrus comes from the ancient Greek mormyros, originally the name of an unrelated marine sea bream and later carried over by naturalists to this African freshwater group. The species name subundulatus combines the Latin prefix sub- ("somewhat" or "near") with undulatus ("wavy"), most likely describing a faint wavy patterning that helps set it apart from its close relatives.
Morphology
Mormyrus subundulatus has the elongated, laterally compressed body typical of its genus, with a long-based anal fin, a dorsal fin set well back toward the tail, and a deeply forked caudal fin. FishBase records a maximum length of about 10.6 in, a modest size for the genus, which includes species reaching 19.7 in or more.
As in all mormyrids, an electric organ near the base of the tail produces a weak, species-specific pulse-type electric-organ discharge (EOD). The fish reads the distortions this field picks up through electroreceptors covering its skin, a sense used to find prey and obstacles and, it is thought, to recognise other mormyrids in dark, sediment-laden water. 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 electrosensory input. Because so many Mormyrus species look nearly identical, confident field identification of this species — as with M. tapirus and M. rume — really depends on the EOD waveform or, as in the study that confirmed it, on fin-ray counts and genetics rather than colour or outline alone. FishBase also flags the genus as sensitive to poor water conditions and to some medications, a trait shared broadly across the family (see "In the aquarium").
Habitat
Mormyrus subundulatus is a freshwater, bottom-dwelling (demersal) fish endemic to two coastal West African river systems: the Bandama in Côte d'Ivoire and the Tano in Ghana. The IUCN assessment notes the species is restricted to these two rivers and considers it likely to have been extirpated from one of them, leaving a genuinely narrow range.
Species-specific water-chemistry data for this fish is sparse in the sources reviewed here. West African lowland rivers of this kind are generally warm, soft and turbid to tannin-stained, the kind of low-visibility water in which the electric sense of mormyrids is thought to have evolved, but precise temperature and pH figures for M. subundulatus specifically are not documented, so those figures should be read as typical of the habitat type rather than measured for this population.
Feeding
Species-specific feeding data for Mormyrus subundulatus is sparse. Mormyrids as a family are nocturnal predators of small benthic invertebrates — insect larvae, worms and small crustaceans — locating prey buried in soft sediment after dark using electrolocation rather than sight, and there is no reason to expect this species differs from that general pattern.
General care guidance for elephant-snout fishes in the aquarium describes a diet of live and frozen foods such as mosquito larvae, bloodworm, white worms, Tubifex, Daphnia and Cyclops, with dry or flake food rarely accepted. That advice comes from care literature covering the family and the more commonly kept elephantnose species rather than from M. subundulatus specifically, so it should be read as a starting point rather than a confirmed diet for this fish.
Mating
Courtship in mormyrids is understood to rely on the electric-organ discharge: differences in the pulse waveform and pattern are thought to let fish recognise species and sex and to play a role in courtship and dominance interactions. Beyond that broad family picture, the mating behaviour of Mormyrus subundulatus specifically has not been documented in the sources available here.
In the wild, mormyrids are generally seasonal spawners tied to flood cycles, when rising water opens up floodplain habitat and food. Whether M. subundulatus follows that pattern in the Bandama or Tano has not been studied in detail; the family's breeding behaviour more broadly remains only partly understood.
Breeding
Breeding of Mormyrus subundulatus in captivity is, as far as the available sources indicate, essentially unrecorded, and mormyrid breeding in general is poorly known and only rarely achieved in home aquaria. The species is also not established in the aquarium trade, which limits any opportunity for hobbyist observation.
Some mormyrids are thought to guard eggs laid among plants or root tangles in the wild, but this has not been confirmed for M. subundulatus. Any claimed captive spawning of this species should be treated as a notable, poorly documented event rather than a repeatable method.
In the aquarium
Mormyrus subundulatus is not established in the aquarium hobby; it is a range-restricted, conservation-listed fish rather than a trade species, and dedicated husbandry information for it does not exist. What follows is general guidance for elephant-snout fishes and should be read as a starting point rather than species-specific advice.
Mormyrids as a family need a soft, sandy or muddy substrate to forage over, dim lighting, and ample hiding places, and they are consistently described as sensitive to water quality — sensitive enough that some species have been used as bioindicators in municipal water testing. Stable, clean, well-filtered water and gentle, copper-free medication are recommended for the family generally. Elephant-snout fishes are usually described as peaceful toward other fish but intolerant of their own kind kept singly or in pairs; care guidance for the family recommends a group rather than a lone individual to spread aggression.
Conservation
The IUCN Red List assesses Mormyrus subundulatus as Vulnerable, under criterion B1ab(iii), in an assessment dated 30 November 2019. The listing reflects a genuinely narrow range: the species is restricted to two rivers, the Bandama and the Tano, and is considered likely to have already disappeared from one of them.
The IUCN cites habitat degradation and overfishing as the relevant threats. With no wider distribution as a buffer, further pressure on either river could have an outsized effect on the species as a whole, and its status is worth monitoring rather than treated as settled.