Taxonomy & naming
Marcusenius schilthuisiae was described by the Belgian-British ichthyologist George Albert Boulenger in 1899. It belongs to the family Mormyridae — the elephantnoses and mormyrids — within the order Osteoglossiformes, the bonytongues: one of the most ancient surviving lineages of ray-finned fish, its name referring to a toothed bone on the floor of the mouth that bites against a matching toothed pad on the roof. The Catalog of Fishes treats Marcusenius schilthuisiae as the valid name, and it is independently catalogued by ITIS (TSN 649887).
The genus Marcusenius is a large, mostly sub-Saharan African group whose species are notoriously difficult to separate by external appearance and are more reliably distinguished, where studied, by the waveform of their electric-organ discharge (EOD) rather than by eye. The species epithet honours Lubbina Schilthuis (1863–1951), a Dutch ichthyologist and curator at the Museum of Zoology of the University of Utrecht — a naming choice notable for recognising a woman scientist at a time when few were credited in the taxonomic literature of the era.
Morphology
Like other mormyrids, Marcusenius schilthuisiae has the family's typical build: a laterally compressed, elongated body, a small, low-set mouth suited to picking invertebrates from the substrate, an elongated dorsal fin set opposite a similarly long-based anal fin, and a deeply forked tail. FishBase records a maximum size of about 5.8 in standard length, making it a modest, small-to-medium mormyrid rather than one of the genus's larger members.
At the base of the tail sits the electric organ, a modified muscle mass that fires the fish's pulse-type discharge many times a second for electrolocation and communication. As in other mormyrids, the brain is disproportionately large for a fish of this size, with an enlarged, richly folded cerebellum dedicated to processing the constant stream of electrosensory information — the physical basis for the family's reputation as unusually intelligent, "thinking" fish. Colouration and fine external detail are not well documented in the sources consulted here; like many Marcusenius, confident field identification likely depends more on locality and EOD signature than on visible pattern.
Habitat
Marcusenius schilthuisiae is known from the middle Congo River basin of the Democratic Republic of the Congo, with FishBase citing a range running from Pool Malebo (Stanley Pool) downstream of Kinshasa to the Ruki River, a Congo tributary further upstream. It has not been reported from any other African river system in the sources available here, and unlike a handful of its more broadly distributed congeners it reads as a basin endemic rather than a wide-ranging species.
FishBase classes it as a demersal, tropical freshwater fish, giving a temperature range of roughly 75–82 °F, a pH around 7.0, and a hardness of about 5–15 dH — circumneutral, soft-to-moderately-hard water. The middle Congo, like much of the wider basin, tends to run dim and often tannin- or sediment-stained, the kind of reduced-visibility water in which a mormyrid's electric sense does the work that eyesight cannot.
Feeding
Species-specific feeding data for Marcusenius schilthuisiae is sparse, but FishBase records a trophic level of about 3.1, consistent with a low-level invertebrate feeder rather than a piscivore. General guidance for the genus notes that wild Marcusenius forage on aquatic insects, insect larvae and small snails, using electrolocation to find prey hidden in mud and cover in poor visibility — a foraging style shared across the family.
In the aquarium, small mormyrids of this type are typically kept on live and frozen insect-based foods — bloodworm, small crustaceans and similar invertebrate fare — rather than dry or vegetable-heavy diets. No aquarium-specific feeding record for this exact species is available in the sources consulted here, so this account follows the documented genus pattern rather than claiming it has been confirmed for M. schilthuisiae itself.
Mating
As in other mormyrids, the electric-organ discharge is thought to play a role in courtship and species recognition, with fish able to detect differences in EOD waveform and pulse rate between individuals and species — a plausible mechanism for mate choice and species isolation in a genus where several similar-looking Marcusenius can occur in the same waters. Whether, or exactly how, this operates in M. schilthuisiae specifically has not been documented in the sources available here.
No field observations of courtship behaviour, spawning season, or site selection for this species are recorded in the cache consulted for this account. Rather than speculate, this account notes the general pattern documented for the family and states plainly that species-specific mating behaviour for M. schilthuisiae is not established in the available literature.
Breeding
Breeding data for Marcusenius schilthuisiae is sparse, and captive breeding is not documented in the sources consulted here. As with most mormyrids, this is consistent with a seasonal, flood-triggered wild spawner whose reproductive biology has never been closely studied and which is essentially never bred under aquarium conditions.
Whatever specimens reach the hobby are understood to be wild-collected rather than farmed. This account does not assign the species a specific breeding mode beyond noting that, like its relatives, it is a poorly known seasonal spawner rather than a fish with an established captive-breeding protocol.
In the aquarium
Marcusenius schilthuisiae is scarcely documented in the aquarium trade, and species-specific care guidance is not available in the sources consulted here. General care guidance for the genus Marcusenius calls for a tank of at least 39.4 in in length, dim lighting and dense hiding — caves, driftwood and planting — since these are shy fish that stress under bright, open conditions, and notes that Marcusenius are social rather than solitary and do better kept in a group.
Mormyrids as a family are markedly sensitive to poor water quality and to some medications, and are best introduced only into a mature, stable, well-cycled tank with soft-to-moderately-hard, circumneutral water reflecting the wild range given above (roughly 75–82 °F, pH around 7.0, 5–15 dH). At a modest maximum of around 5.9 in this species is not the size trap that some larger mormyrids and arowanas are, but as with the rest of the family it remains a specialist's fish rather than a beginner community option, and any specimen offered for sale should be assumed wild-caught.
Conservation
The IUCN Red List assesses Marcusenius schilthuisiae as Least Concern, an assessment dated 16 February 2009. FishBase similarly reports a low estimated vulnerability to fishing pressure for the species.
As a basin endemic known only from a limited stretch of the middle Congo River, the species is not widely distributed, but no specific threats are documented in the sources consulted here, and it is not currently considered at elevated risk. As with other Congo basin fish, broader long-term pressures — habitat disturbance, water-quality change and the general difficulty of monitoring fish in a large, remote river system — are the general context rather than documented species-specific concerns.