Taxonomy & naming
Hippopotamyrus macroterops was described by the Belgian-British ichthyologist George Albert Boulenger in 1920, with the type locality given as Poko in Haut-Zaïre — the Upper Congo River drainage of what is now the Democratic Republic of the Congo. It belongs to the family Mormyridae, the elephantnoses and mormyrids, within the order Osteoglossiformes — the bonytongues, one of the most ancient living branches of the teleost fishes, named for a toothed bone on the floor of the mouth that bites against a toothed plate on the roof. Mormyridae is an exclusively African radiation that, together with the related Gymnarchidae, forms the weakly electric Mormyriformes; despite a superficial resemblance in some relatives, it is entirely unrelated to the electric knifefishes (Gymnotiformes) of South America — a case of pure convergent evolution across two separate continents and lineages.
Mormyrid systematics remain unsettled, and this species is a good example: a mitochondrial-DNA analysis of the holotype has recently proposed reclassifying it into the genus Pollimyrus, as the combination Pollimyrus macroterops. That molecular revision has not displaced the historical placement everywhere, and this article follows the longer-established combination, Hippopotamyrus macroterops, while noting that the genus assignment is actively under review rather than settled fact.
The epithet macroterops most plausibly derives from Greek makroteros, the comparative of makros ("large", i.e. "larger"), combined with ops ("eye") — literally "larger-eyed." That reading lines up neatly with the already-described congener Hippopotamyrus macrops ("large-eyed"), suggesting Boulenger may have coined the name in direct comparison with that earlier species, though the precise reasoning given in the original 1920 description is not confirmed here.
Morphology
Hippopotamyrus macroterops has the typical mormyrid build: an elongate, laterally compressed body, a small, roughly terminal mouth, and no long, probing chin appendage of the kind seen in Gnathonemus petersii and some related genera. No total-length figure specific to this species could be confirmed here; congeners across Hippopotamyrus range widely, from around 3.5 in to over 9.8 in total length depending on species, and a modest to moderate size somewhere in that range is a reasonable expectation rather than a documented record for macroterops itself.
Like every mormyrid, it carries an electric organ in the caudal peduncle, derived from modified muscle tissue, that produces a continuous, low-voltage, species-specific pulse-type electric organ discharge (EOD). The EOD is read by electroreceptors distributed across the skin and used to electrolocate — building a moving picture of obstacles, prey and open water in the dark, sediment- and tannin-stained rivers of the Congo Basin — and to signal to other fish of the same species. Mormyrids as a family have among the highest brain-to-body mass ratios of any vertebrate, with an enlarged cerebellum devoted largely to processing this electrosensory picture; H. macroterops shares this general mormyrid neuroanatomy, though its own brain has not been separately studied.
Habitat
Hippopotamyrus macroterops is known from the Upper Congo River drainage in the Democratic Republic of the Congo, with its type locality at Poko in the former Haut-Zaïre province. It is a Congo Basin endemic, and the available records suggest a narrow, poorly surveyed range rather than a wide one — data on its full distribution remain sparse.
Habitat descriptions for the species point to dark, tannin-stained African river and floodplain water with dense marginal vegetation, the low-visibility conditions that favour an electric sense over vision. No precise water-chemistry measurements have been published for this species specifically; like most Congo Basin mormyrids it almost certainly lives in warm, soft water on the acidic-to-neutral side, in keeping with the blackwater and floodplain habitats typical of the wider basin. The Congo system is one of the most species-rich and least-studied river basins on Earth, and much of its mormyrid diversity, including this species, remains poorly known.
Feeding
As in other mormyrids, Hippopotamyrus macroterops almost certainly forages on small aquatic invertebrates — insect larvae, worms and tiny crustaceans — picked out of sediment and cover using electrolocation rather than eyesight, mostly after dark. No feeding study specific to this species has been documented here.
Because Hippopotamyrus as a genus is only rarely, if ever, seen in the aquarium trade, there is essentially no captive feeding record for macroterops to draw on. Small mormyrids that do reach hobbyists generally take live and frozen invertebrate foods such as bloodworm and brine shrimp readily once settled, and that is a reasonable general expectation rather than a confirmed fact for this particular species.
Mating
Mormyrid courtship is built around the electric organ discharge: in better-studied genera, males use their EOD waveform and pulse pattern in courtship displays to signal species identity and readiness to spawn, and females appear to select mates partly on EOD characteristics. Whether Hippopotamyrus macroterops follows this pattern has not been documented — it is inferred from the wider family rather than observed directly in this species.
Congo Basin mormyrids are generally understood to be seasonal, flood-triggered spawners, with reproduction cued to the seasonal rise in river level and the flooding of marginal vegetation, which likely provides both spawning cover and food for fry. No details of pairing, courtship duration or spawning site have been recorded for H. macroterops.
Breeding
Breeding biology in Hippopotamyrus macroterops is essentially undocumented. What little is known of the genus and its Congo Basin relatives points to seasonal, flood-triggered spawning in the wild, but the details are barely understood, and captive breeding of this species is rarely, if ever, achieved — the genus is too scarce in the hobby for a reliable spawning record to exist.
Some mormyrids are thought to scatter eggs among submerged plants or root mats with little further parental care; without direct observation it would be guesswork to assign that or any other specific pattern to H. macroterops. The honest summary is that its reproductive biology, in the wild and especially in captivity, remains a research gap rather than a documented fact.
In the aquarium
Hippopotamyrus macroterops is not, in any practical sense, an aquarium fish. The genus Hippopotamyrus is considered particularly rare in the hobby generally, and this species in particular has essentially no track record in captivity — prospective keepers should treat any care advice here as inferred from the wider mormyrid family, not as tested experience with macroterops itself.
General mormyrid husbandry principles would apply if it were ever available: a dimly lit tank with ample hiding places (driftwood, roots, dense planting), stable, soft water, and a diet of live or frozen invertebrates such as bloodworm and brine shrimp offered mostly after dark, since mormyrids are shy, largely nocturnal fish that grow stressed under bright light or in bare tanks. As a family, mormyrids are notably sensitive to poor water quality and to many medications — dosing should be conservative and water quality kept high. A species tank or small group, rather than a boisterous community, is the usual recommendation for mormyrids in general, though nothing about grouping or aggression has been specifically documented for H. macroterops.
Conservation
The IUCN Red List lists Hippopotamyrus macroterops as Data Deficient, meaning there is not enough information on its population, range or trends to assess extinction risk one way or the other — a status distinct from, and not a substitute for, a clean bill of health. The recent proposal to reclassify the species into Pollimyrus adds a further layer of uncertainty, since conservation assessments are tied to a specific accepted name and taxonomic instability can complicate tracking a species' status over time.
That data gap should be read against the wider context of the Congo Basin, one of the world's least-studied major freshwater systems, where habitat pressures such as deforestation, mining-related sedimentation and future hydropower development are recognised long-term threats to the basin's mormyrid diversity even where, as here, an individual species' status cannot yet be properly assessed. It is not the target of any aquarium fishery, so trade pressure is not considered a factor in its case.