Taxonomy & naming
Myomyrus macrops was described by the Belgian-British ichthyologist George Albert Boulenger in 1914. It belongs to the family Mormyridae within the order Osteoglossiformes, the bonytongues, a scattered and ancient radiation of freshwater fishes found on four continents and united by an ossified, toothed structure on the tongue that opposes teeth on the roof of the mouth. Mormyridae itself is an exclusively African family of weakly electric fishes, unrelated to the superficially similar electric knifefishes of South America (order Gymnotiformes) despite the two groups arriving at electroreception independently.
The genus name Myomyrus is thought to combine the Greek myos, the genitive of "mouse", with -myrus, the conventional suffix used for elephantfish genera and taken from Mormyrus, the family's type genus; the mouse reference is usually read as an allusion to the large, incisor-like teeth seen in some species of the genus. Myomyrus is treated as the sister lineage to the rest of the subfamily Mormyrinae, making it one of the more basal branches in the mormyrid family tree. Myomyrus as a whole is restricted to the Congo River basin, and macrops is one of a small number of species placed in it.
Morphology
Reported maximum size for Myomyrus macrops is about 9.8 in total length. As in other mormyrids the body is laterally compressed and the tail narrows to a slender caudal peduncle housing the electric organ, a modified muscle bundle near the base of the tail that generates a weak, species-specific pulse discharge. The species name macrops refers to conspicuously large eyes relative to other elephantnoses, though like most mormyrids it still relies primarily on electrolocation rather than vision to find its way and its food in dark water.
Detailed published description of body form, coloration and fin proportions specific to M. macrops is sparse, and this account does not go further than the confirmed points above. Mormyrids in general have a mouth (terminal to subterminal depending on species), no adipose fin, and stiff pectoral fins used for slow, hovering movement — control that suits a fish reading its surroundings through a continuously emitted electric field rather than swimming fast through open water.
Habitat
Myomyrus macrops is known from the middle and upper reaches of the Congo River basin, with records from the Democratic Republic of the Congo and Cameroon. It is a freshwater, demersal fish, living near the bottom rather than in open water.
Surveys of Congo basin tributaries describe the mormyrid community of these upstream reaches as occupying shallow water over silt substrates, in calm to gently flowing stretches — the dim, vegetated pools typical of old-growth forest tributaries in the basin. That kind of tannin-stained, low-visibility water is exactly the setting in which a weak electric sense is most useful: sight is of limited value, and the fish reads its surroundings and locates prey through its self-generated electric field instead.
Feeding
No feeding study specific to Myomyrus macrops is available, so what follows is drawn from what is known of mormyrids generally rather than from data on this species. Elephantnoses as a group are benthic foragers, using electrolocation to detect insect larvae, small crustaceans, worms and other invertebrates buried in sand, silt or leaf litter, typically feeding after dark or at dusk when they are least conspicuous to predators.
In the aquarium, mormyrids as a group take live and frozen invertebrate foods readily — bloodworm, brine shrimp and tubifex are the standard staples — and are generally reluctant to accept dry or flake foods. Feeding after lights-out, matching their natural low-light foraging window, is the usual way to get a shy specimen eating reliably.
Mating
Courtship and spawning behaviour in mormyrids more broadly is understood only in outline: the electric organ discharge (EOD), in addition to its role in orientation, doubles as a signal used in species recognition and courtship, with pulse pattern and rate varying between species and, in some cases, between sexes. Wild mormyrids are believed to be seasonal spawners tied to the rains and to rising floodwater, which would open access to flooded margin habitat and trigger breeding condition.
Nothing specific to Myomyrus macrops has been published on courtship behaviour, pairing, or spawning sites, and this account does not speculate beyond the general pattern known for the family.
Breeding
Myomyrus macrops has essentially not been bred in the aquarium, and breeding biology across the mormyrid family is poorly documented even in the wild. What little is known points to seasonal, flood-triggered spawning, with some mormyrids thought to scatter or deposit eggs among submerged vegetation and offer some degree of guarding, but the details for most species, including this one, have not been worked out.
Mormyrids are also difficult aquarium subjects generally — sensitive to water quality, slow to settle, and rarely reaching the kind of stable, long-term condition in captivity that would make deliberate breeding attempts practical. For M. macrops specifically, captive reproduction should be treated as essentially unachieved and the underlying biology as still largely unknown.
In the aquarium
Myomyrus macrops is rarely if ever seen in the trade, and this account draws on general mormyrid husbandry rather than species-specific keeping reports. Elephantnoses as a group are sensitive to poor water conditions and do best in soft, acidic-to-neutral, stable water with dim lighting and ample cover — driftwood, plants and shaded refuges that let a naturally shy, nocturnally active fish feel secure during the day. A fine sand or smooth gravel substrate is preferable to sharp gravel, since some mormyrids probe the bottom with the snout while foraging and can abrade or injure it on coarse material. A single fish is generally recommended a tank of at least 50 US gal; mormyrids can be intolerant of their own kind and of other electrogenic species in a confined space.
A critical care point for the whole family: mormyrids are notably intolerant of copper, formalin, dyes and salt in medications, so routine disease treatments used on other fish can be lethal and should be avoided or used at reduced, carefully researched doses. Given how rarely this particular species is kept and how sparse the published husbandry record is, anyone acquiring M. macrops should treat general mormyrid guidelines as a starting point rather than a confirmed recipe, and expect a demanding, poorly documented fish rather than an easy community addition.
Conservation
The IUCN Red List assesses Myomyrus macrops as Least Concern, an assessment dated 16 February 2009, with no major threats documented at that time.
As with much of its biology, up-to-date population trend data specific to this species is not readily available, and the Least Concern rating reflects a wide-ranging, apparently stable presence within the Congo basin rather than active recent monitoring. General pressures on Congo basin freshwater habitat — deforestation, sedimentation and localised fishing pressure — are the relevant long-term concerns for the region's mormyrid fauna as a whole.