Taxonomy & naming
Ivindomyrus marchei was described by the French zoologist Henri Émile Sauvage in 1879 as Mormyrus marchei, from material collected by the French explorer and naturalist Alfred Marche (1844–1898) on the Ogooué River at Doumé — territory then administered under the French Congo, the colonial holding later split into Gabon and the Republic of the Congo. The species belongs to the family Mormyridae within the order Osteoglossiformes, the bonytongues: a scattered, deep-time radiation of fishes found on four continents (South America, Africa, Southeast Asia and Australasia) and united by that toothed lingual bone rather than by any shared modern habitat. The Mormyridae are an exclusively African family of several hundred species, all weakly electric, and entirely convergent with — not related to — the electric knifefishes of South America (Gymnotiformes); the two lineages evolved similar electric senses independently on opposite sides of the Atlantic.
The parenthetical authority "(Sauvage, 1879)" signals that the species has moved genus since its original description, and its synonymy is unusually busy even by mormyrid standards: over the decades it has also been classified as Marcusenius marchii and Petrocephalus marchei before landing in the small genus Ivindomyrus. That bouncing between Mormyrus, Marcusenius, Petrocephalus and Ivindomyrus reflects how difficult mormyrids are to sort by external appearance alone — close relatives can look near-identical, and species boundaries in the family are often settled only by fine skeletal characters or by each species' distinctive electric organ discharge (EOD), not by eye. The genus name Ivindomyrus most likely combines the Ivindo River — a major tributary of the Ogooué in Gabon — with the Greek myros/-myrus ("eel"), a suffix common across mormyrid genus names (as in Mormyrus itself) that alludes to the family's elongate, eel-like build.
Morphology
Ivindomyrus marchei is a small mormyrid: FishBase records a maximum of 7.1 in standard length, placing it well below the larger trunk-snouted elephantnoses and the bigger Mormyrus species that can exceed half a metre. Its history of being confused with the short-snouted genus Petrocephalus is telling — unlike the famous elephantnose Gnathonemus petersii, whose elongated, worm-probing chin appendage (the Schnauzenorgan) is one of the most recognisable structures in freshwater fishkeeping, Ivindomyrus is not known to carry that kind of extended trunk. It is built instead along the more generalised, elongate mormyrid body plan: a moderately compressed trunk, a dorsal fin set well back toward the tail, and a forked caudal fin, in the muted silvery-grey to olive-brown tones typical of the family that help camouflage a fish moving through turbid or tannin-stained water.
As in every mormyrid, an electric organ near the base of the tail generates a weak, species-specific, pulse-type electric organ discharge (EOD), used to electrolocate prey and obstacles in the dark and to communicate with other mormyrids. The family as a whole is celebrated for having some of the highest brain-to-body mass ratios of any fish, with an outsized cerebellum dedicated to processing this electrosensory stream — a genuine physiological trade-off for a fish that reads its world electrically rather than visually.
Habitat
Ivindomyrus marchei is known from the Ogooué and Nyanga River systems of Gabon, in Central Africa — a narrow-range endemic rather than a wide-ranging species. The type material was collected at Doumé on the Ogooué, and FishBase lists the species as a freshwater, demersal fish of tropical West-Central African rivers.
No species-specific water-chemistry data appears to have been published for I. marchei — FishBase records none. What can be said comes from the general biology of Central African mormyrids and of the Ogooué basin itself: warm, typically soft and slightly acidic to neutral river and floodplain water, often tannin-stained by decaying leaf litter and forest cover, which is precisely the low-visibility environment in which an electric sense outperforms eyesight. That should be read as a reasonable inference from the habitat type rather than a measurement taken on this fish.
Feeding
Like other mormyrids, Ivindomyrus marchei is presumed to be a nocturnal forager that relies on active electrolocation to detect small aquatic invertebrates — insect larvae, worms and small crustaceans — hidden in soft substrate and among cover, hunting confidently after dark or in turbid water where sight offers little advantage. No dedicated dietary study of this species appears in the available sources, so this picture is extrapolated from mormyrid biology generally rather than confirmed for I. marchei specifically.
Were it kept, aquarium care guides for mormyrids in general recommend live and frozen invertebrates — bloodworm and brine shrimp foremost — offered over a soft substrate, ideally after lights-out to match a nocturnal feeding rhythm.
Mating
Courtship and reproductive behaviour in Ivindomyrus marchei have not been described in the available sources — this is a poorly studied, narrow-range species with no dedicated field or aquarium breeding account. As in other mormyrids, mate and species recognition is thought to run substantially through the electric organ discharge rather than through visual display, with each species' EOD pattern likely serving as a kind of electrical signature, but the specific courtship behaviour of this species is simply not documented.
More broadly, mormyrid reproduction across the family tends to be seasonal and tied to rainfall and rising floodwaters, but whether that pattern holds for I. marchei in the Ogooué and Nyanga systems has not been confirmed in the literature reviewed here.
Breeding
Ivindomyrus marchei has essentially never been bred in captivity, and — as with the great majority of mormyrids — its wild breeding biology is poorly known. It is reasonable to expect it follows the family's general pattern of seasonal, flood-triggered spawning, but no published account describes spawning sites, egg-laying, or parental behaviour for this particular species.
This is not a fish with an established aquarium breeding history to draw on; it does not appear to be established in the ornamental trade at all. Anyone encountering it should treat any breeding attempt as genuinely unexplored territory rather than following a known protocol.
In the aquarium
Ivindomyrus marchei is not an established aquarium species — it does not turn up in the hobby trade, and no dedicated species-specific husbandry account exists. What follows is drawn from general mormyrid care rather than experience with this fish in particular, and should be read with that caveat. General mormyrid guidance calls for dim lighting, soft substrate, ample driftwood and root cover, and stable, non-turbulent water; mormyrids are notably sensitive to poor water quality and to many medications (copper-based treatments especially), so any dosing in a mormyrid tank calls for real caution.
Mormyrids can also be territorial and quarrelsome toward their own kind, sparring over space and over their individual electric "signature", so a solitary specimen or a genuinely large, well-furnished tank would be the safer approach if this species were ever kept. Given how little is documented about I. marchei specifically, anyone acquiring it should treat it as an expert-only, poorly understood fish rather than a straightforward community addition.
Conservation
The IUCN Red List has assessed Ivindomyrus marchei as Least Concern (assessment recorded 2009). It is endemic to a fairly narrow slice of Central Africa — the Ogooué and Nyanga River systems of Gabon — but is not currently considered threatened.
That narrow range is nonetheless worth keeping in view: a species restricted to two river systems in a single country has less of a buffer against habitat pressure than a fish spread across a continental-scale basin. Gabon's Ogooué basin remains relatively forested and lightly developed compared with many African rivers, which likely underpins the current Least Concern status, but logging, mining and future hydrological change in the basin are the kind of generic pressures that could matter for a range-restricted species like this one over time.