Taxonomy & naming
Hippopotamyrus harringtoni was described by the Belgian-British ichthyologist George Albert Boulenger in 1905, with a type locality on the White Nile River in Sudan. It belongs to the family Mormyridae within the order Osteoglossiformes, the bonytongue fishes — an ancient, deep-time radiation found today on four continents (South America, Africa, Southeast Asia and Australasia) that also includes the arowanas, arapaima, African butterflyfish and the featherback knifefishes, none of which are closely related to the superficially similar electric knifefishes of South America.
Modern molecular and mitogenomic work on the mormyrids, published in a taxonomic revision in ZooKeys, treats Hippopotamyrus harringtoni as a junior synonym of the earlier-described Hippopotamyrus pictus (Marcusen, 1864); the type material and taxonomic history behind the synonymy have been resolved in that study. In practice this means the fish historically labelled harringtoni from the White Nile is now regarded as part of a single, wider-ranging species, H. pictus, even though the name harringtoni is still what turns up attached to Sudanese White Nile records and to some older hobby and survey literature. The genus name Hippopotamyrus combines the Greek hippopotamos ("river horse") with a suffix echoing Mormyrus, the type genus of the family; the species epithet harringtoni is a Latinised patronym, honouring a collector named Harrington associated with the type material.
Morphology
Like other mormyrids, Hippopotamyrus harringtoni has the family's characteristic build: a laterally compressed body, a small, near-toothless-looking mouth, weak eyesight, and no barbels. Set into the caudal peduncle near the tail is an electric organ that fires a weak, species-specific pulse-type electric-organ discharge (EOD), which the fish uses to electrolocate obstacles, prey and other fish in dark or turbid water, and to communicate — courtship and dominance signalling both run through the EOD. Mormyrids as a family are also known for having one of the highest brain-to-body mass ratios of any fish group, built around a greatly enlarged cerebellum that processes the constant stream of electrosensory information; they are sometimes called "thinking fish" for it.
FishBase reports a maximum length of about 12 in total length for Hippopotamyrus pictus, the species harringtoni is now synonymised with. Aquarium imports of Hippopotamyrus, when they appear in the trade at all, are typically wild-caught juveniles well under that figure and grow slowly, so a keeper should plan tank space for the adult size rather than the size at purchase.
Habitat
The confirmed record for Hippopotamyrus harringtoni is the White Nile River system in Sudan, documented both by the original type locality and by a more recent survey of Sudan's freshwater fish fauna; exact localities and depth range within that system are not well documented (data sparse). As Hippopotamyrus pictus sensu lato, the wider taxon it has been synonymised with, the species is reported across a broad swath of Sahelo-Sudanese Africa — the Nile, Niger, Benue, Chad and Volta river basins — with additional records from the Mono River in Togo and the Sassandra River in Côte d'Ivoire, so the true range of the White Nile population within that pattern is not precisely mapped.
FishBase gives a temperature range of roughly 72–75 °F for the species, consistent with a warm, freshwater, bottom-dwelling (demersal) fish of African rivers and their floodplains. Like other mormyrids it is presumed to favour turbid, silt- or tannin-stained water, the kind of low-visibility habitat its electric sense is built to read, though specific water-chemistry data for this population is not available in the sources consulted.
Feeding
Specific dietary data for Hippopotamyrus harringtoni was not found in the sources consulted, but the mormyrid family as a whole is predominantly insectivorous and invertebrate-feeding, taking aquatic insect larvae, small crustaceans and other benthic invertebrates picked out of sand or silt using the electric sense to locate prey that eyesight alone could not find in murky water.
In the aquarium, mormyrids generally are fed live or frozen invertebrate foods — bloodworm and brine shrimp are the staples cited for the group — offered after lights-out, since most species forage mainly at night and can be out-competed for food by more active daytime tankmates.
Mating
Detailed courtship behaviour has not been described for Hippopotamyrus harringtoni specifically, but mormyrids in general use their electric-organ discharge in courtship and species recognition — the pulse pattern itself is thought to help fish identify a compatible mate of the right species, since many mormyrids look superficially alike and are more reliably told apart by their EOD than by external appearance.
In the wild, mormyrids as a group are seasonal, flood-triggered spawners, timing reproduction to the rains and the resulting rise in river and floodplain water levels. The finer details of pair formation and spawning behaviour in this species remain poorly known.
Breeding
Hippopotamyrus harringtoni is essentially not bred in the aquarium hobby, and its breeding biology is poorly understood even in general terms. As with mormyrids as a group, wild spawning appears to be a seasonal event cued to flooding, and there is some suggestion that certain mormyrids guard their eggs among vegetation, but this has not been specifically documented for this species.
Captive breeding of mormyrids of any kind is rarely if ever achieved by hobbyists; the electric organs, poorly known courtship cues and the group's general sensitivity to captive conditions all work against it. Anyone keeping this fish should treat it as a long-term display animal rather than a breeding project.
In the aquarium
Mormyrids including Hippopotamyrus are demanding, specialist fish rather than casual community stock. They do best in soft, dimly lit water with plenty of hiding places and a soft substrate they can probe, mirroring the turbid, sediment-laden rivers their electric sense evolved to read; harsh lighting and bare, brightly lit tanks stress them. They are notably sensitive to poor water quality and to many medications — treat cautiously and avoid copper-based products — and conspecifics can be aggressive toward one another, so tank mates and grouping need care rather than a default assumption of shoaling peace.
Because Hippopotamyrus harringtoni is now regarded as a junior synonym of Hippopotamyrus pictus, fish offered in the trade under either name may in practice be the same species; buyers should expect uncertainty in labelling rather than a guaranteed distinct "harringtoni" fish. As with all mormyrids, quarantine and acclimation deserve extra caution, since wild-caught imports typically arrive stressed and are known to be delicate in transit.
Conservation
FishBase records the IUCN Red List status for Hippopotamyrus pictus — the taxon Hippopotamyrus harringtoni is now synonymised with — as Least Concern, an assessment dated to 2019. This reflects a wide-ranging species across multiple Sahelo-Sudanese river basins rather than a narrow, single-locality endemic, so there is no indication of elevated extinction risk at the whole-taxon level.
No species-specific population trend or threat data for the White Nile population was found in the sources consulted. As with other Nile and Sahelo-Sudanese river fishes, general pressures on the group are the usual ones for African river systems — damming, siltation, water abstraction and overfishing — rather than any threat documented specifically for this fish.