Taxonomy & naming
Hippopotamyrus weeksii was described by the Belgian-British ichthyologist George Albert Boulenger in 1902. It belongs to the family Mormyridae — the elephantnoses and mormyrids — which with more than 230 described species is the largest family within the Osteoglossiformes, the ancient bonytongue order that also holds the arowanas, the arapaima, the African butterflyfish and the Old World featherback knifefishes. The Osteoglossiformes are one of the earliest-diverging lineages of living teleost fishes, a deep-time radiation scattered by continental drift across South America, Africa, Southeast Asia and Australasia; H. weeksii represents the African, electric-sensing branch of that story.
The species' generic placement has moved more than once, a common pattern in a family whose species are hard to tell apart by eye and are increasingly sorted by their electric discharge and by genetics rather than by external anatomy alone: it has been carried under Marcusenius and Hippopotamyrus, and more recent taxonomic treatments place it in Cyphomyrus. This account follows the Hippopotamyrus placement and the authority (Boulenger, 1902); readers researching further should be aware the same fish may appear under a different generic name depending on the source's publication date. The species epithet honours the Reverend John Henry Weeks (1861–1924), a Baptist missionary and naturalist who explored and collected extensively along the upper Congo River; the holotype was collected at the Monsembe mission station on that river, in what is now the Democratic Republic of the Congo.
Morphology
Hippopotamyrus weeksii has the compact, deep-bodied build typical of its genus name (hippopotamyrus loosely evokes a stout, "hippo-like" mormyrid shape), with a short, blunt snout rather than the long trunk-like chin appendage — the schnauzenorgan — that makes some of its Mormyridae relatives, such as the elephantnose Gnathonemus petersii, so distinctive. The mouth sits low and small, suited to picking food items directly off or out of the substrate rather than probing at a distance.
Like all mormyrids it carries a specialised electric organ near the base of the tail, built from modified muscle cells (electrocytes), which generates a brief, low-voltage pulse-type discharge. Surrounding the body is a dense field of electroreceptors that read the distortions this pulse creates as it passes through nearby objects, water of varying conductivity, and other fish — an active sensory system, electrolocation, that lets the fish build a picture of a dark, cluttered environment without relying on vision. Mormyrids as a group are also known for having among the highest brain-to-body mass ratios of any fish, with an enlarged cerebellum devoted to processing this electrosensory stream; H. weeksii shares this same basic neural architecture, even though its brain has not specifically been studied. Because so many small mormyrid species look broadly alike, confident field identification in this genus often relies on the individual electric organ discharge (EOD) waveform as much as on external anatomy — a caveat worth keeping in mind for any account of this size range.
Habitat
Hippopotamyrus weeksii is native to the upper Congo River basin in the Democratic Republic of the Congo, where the type series was collected at Monsembe on the main Congo channel. As with most Congo basin mormyrids, it is a fish of dim, structurally complex water — slow side-channels, flooded margins and sheltered stretches over sand or fine gravel, often stained by tannins from decaying leaf litter to the point that visibility is very limited. That gloom is exactly the environment the electric sense evolved to read: where eyesight fails, the electric-organ pulse and its receptor field keep working.
Detailed field data on this particular species' temperature and chemistry preferences have not been published, and the wider distribution beyond the Congo basin is not well documented in the available literature — a common gap for small, non-commercial mormyrids that attract little research attention outside targeted taxonomic revisions. What is well established for Congo basin mormyrids generally, and is consistent with the aquarium-care sources available for this species, is warm water in the mid-to-high twenties Celsius, soft and slightly acidic to neutral chemistry, and reduced light.
Feeding
In the wild, mormyrids of Hippopotamyrus' build and mouth shape forage over sand and fine sediment for small invertebrates — insect larvae, worms and other benthic prey — locating them as much by electrolocation as by sight, especially after dark when the species is most active. The blunt snout and low-set mouth of H. weeksii fit this pick-off-the-bottom style of feeding rather than the deep-probing style of the long-snouted elephantnoses.
In the aquarium it takes live and frozen invertebrate foods readily — bloodworm, brine shrimp and similar small live or frozen fare are the standard diet reported for this species — and it should be fed after the lights go down, when its natural activity peaks and it is not out-competed by more visually driven tankmates.
Mating
Courtship and species recognition in mormyrids are thought to run substantially through the electric-organ discharge: because each species (and in some cases each sex) produces a subtly different EOD waveform and pulse rate, the discharge is presumed to help fish identify potential mates and rivals of their own kind in murky water where visual cues are limited. Beyond that general pattern, which is inferred from work on better-studied mormyrid genera, essentially nothing specific has been documented about courtship behaviour in Hippopotamyrus weeksii itself, and this account does not extend those better-studied genera's details onto this species.
Wild mormyrids are generally understood to be seasonal spawners cued to rainy-season flooding, when rising water opens up flooded vegetation and marginal habitat for spawning and, presumably, for young fish to shelter in. Whether H. weeksii follows that same pattern has not been confirmed in the literature available for this account.
Breeding
Mormyrids as a group are essentially not bred in captivity, and Hippopotamyrus weeksii is no exception — there are no reliable aquarium breeding reports for this species. What little is understood about mormyrid reproduction in the wild points to flood-triggered, seasonal spawning, with the electric-organ discharge playing some role in courtship or species recognition, and some genera in the family are thought to guard or tend eggs among submerged plants or root tangles after spawning; but the details for this particular species are simply not documented.
Given that gap, the honest summary for a fishkeeper is that H. weeksii should be treated as effectively unbreedable in the home aquarium at present, and that any fish in the trade are wild-caught rather than captive-bred. This is typical of the family: only a small handful of mormyrid species have ever been spawned under aquarium conditions, and this is not one of them.
In the aquarium
Hippopotamyrus weeksii is a specialist fish for an experienced keeper rather than a beginner community addition. Like other mormyrids it is notably sensitive to poor or fluctuating water quality and does best in soft, slightly acidic to neutral water held in the mid-to-high twenties Celsius, kept scrupulously clean and stable; sudden swings in chemistry or the buildup of organic waste are poorly tolerated. Subdued lighting, a fine sand or smooth gravel substrate (coarse or sharp material can abrade the snout as the fish forages), and plenty of hiding places — root tangles, driftwood, broken pots or dense planting — help it settle, since it is a shy, mostly nocturnal fish that wants secure retreats for the day.
Mormyrids are also known to be sensitive to many common aquarium medications, and copper-based treatments in particular should be avoided; any medicating should be done cautiously and only when necessary. Individually kept mormyrids can be territorial or outright intolerant of their own species and of other electric fish sharing overlapping electric fields, so tankmates and stocking density need care — a single specimen in a peaceful, non-electric community, or a proven compatible grouping with generous space and sightline breaks, are the safer approaches; there is no well-documented, reliable formula for keeping this particular species in groups. As with all mormyrids, it should not be confused with the superficially similar-looking but taxonomically unrelated electric knifefishes of South America (Gymnotiformes) — the resemblance between the two groups is convergent, not close kinship.
Conservation
Hippopotamyrus weeksii has not been formally assessed by the IUCN Red List and is listed as Not Evaluated. This is common among small, non-commercial mormyrids restricted to African river systems that receive little targeted conservation research; a Not Evaluated status reflects an absence of assessment rather than any evidence of decline.
The upper Congo basin the species inhabits faces the general pressures common to much of Central African freshwater habitat — deforestation-driven sedimentation, water pollution near population centres, and localised habitat disturbance — but no species-specific population data or threat assessment exists for H. weeksii in the sources available for this account. As with many small, poorly studied mormyrids, the honest position is that its conservation status is genuinely unknown rather than reassuring.