Taxonomy & naming
Gnathonemus echidnorhynchus was described by the French ichthyologist Jacques Pellegrin in 1924. It sits in 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 themselves 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 groups evolved similar electric senses independently on opposite sides of the Atlantic.
The genus name Gnathonemus derives from Greek gnathos, "jaw", and nema, "thread", a reference to the slender, thread-like extension of the lower jaw that forms the family's signature chin organ. The species epithet echidnorhynchus draws on Greek echidna, "viper" or "snake", and rhynchos, "snout", describing the fish's narrow, elongated snout profile. Many mormyrids are superficially similar to one another and are reliably told apart only by their species-specific electric organ discharge (EOD), so visual identification of this species against its Congo-basin relatives should be treated with appropriate caution.
Morphology
Like other members of the genus, Gnathonemus echidnorhynchus has a laterally compressed body and carries a fleshy, downturned extension of the lower jaw and chin — a Schnauzenorgan, densely packed with electroreceptors, used to probe soft substrate for buried prey. An electric organ near the base of the tail generates a weak, pulse-type electric organ discharge (EOD) used for electrolocation and communication in dark water, and mormyrids as a group are noted for having some of the highest brain-to-body ratios of any fish, built around an enlarged cerebellum that processes the constant stream of electrosensory information.
FishBase records a maximum size of about 4.3 in standard length, making this a considerably smaller fish than the well-known aquarium elephantnose G. petersii, which reaches over twice that length. Beyond the basic body plan and size, detailed morphological description in the available sources is limited; data on this species is comparatively sparse next to its more widely studied relatives.
Habitat
Gnathonemus echidnorhynchus is endemic to the Democratic Republic of the Congo, recorded from the Kasai and Kwilu rivers downstream to Wagenia Falls in the middle Congo River basin. This places it firmly within the Congo's vast, slow-flowing, often tannin-stained river system — precisely the kind of dim, low-visibility water in which an electric sense outperforms eyesight.
Detailed water-chemistry data specific to this species is not available in the sources consulted, but the middle Congo basin generally runs warm and on the soft, slightly acidic side, consistent with the sediment-laden, densely vegetated floodplain and river-margin habitat typical of Congo-basin mormyrids. As a narrow-range endemic restricted to a defined stretch of one river system, this is a fish whose ecology is comparatively data-sparse.
Feeding
As a mormyrid, Gnathonemus echidnorhynchus is presumed to be a nocturnal bottom-forager in the manner of its relatives, using the Schnauzenorgan's electroreceptor field together with active electrolocation to sweep the substrate for small invertebrates buried in sand or sediment. No species-specific dietary study is recorded in the available sources, so this account extrapolates from the well-documented feeding behaviour of the genus rather than from direct observation of G. echidnorhynchus itself.
This species is not established in the aquarium trade, so there is no body of hobbyist feeding experience to draw on; any care information would need to be extrapolated cautiously from better-known Gnathonemus such as G. petersii.
Mating
Courtship and species/sex recognition in mormyrids run substantially through the electric organ discharge rather than through visual display, with the pulse pattern thought to carry information about species identity, sex and breeding readiness in genus members that have been studied. No courtship behaviour has been documented specifically for Gnathonemus echidnorhynchus; the wild reproductive biology of this species is essentially unrecorded in the sources available.
Mormyrids in general are thought to be seasonal, flood-triggered spawners, with breeding activity tied to the rains and rising water that mark the Congo basin's wet season, but whether this pattern holds for G. echidnorhynchus specifically has not been confirmed.
Breeding
Gnathonemus echidnorhynchus is essentially not bred in captivity, and its reproductive biology is poorly known even in the scientific literature — it is not established in the aquarium hobby at all. Wild mormyrids as a group are believed to be seasonal, flood-triggered spawners, and the species-specific EOD likely plays a courtship or mate-recognition role, but the details of nest site, egg-laying and any parental behaviour have not been documented for this species.
Some mormyrids are thought to guard eggs among vegetation, but this has not been confirmed for G. echidnorhynchus. There is nothing in the available sources to suggest this fish has ever been spawned in an aquarium.
In the aquarium
Gnathonemus echidnorhynchus is not a species seen in the aquarium trade, and none of the sources consulted describe aquarium husbandry specific to it. Where care guidance is needed, aquarists should extrapolate cautiously from the well-documented needs of the genus, exemplified by G. petersii: soft sand substrate rather than sharp gravel (to avoid injuring the electroreceptor-packed Schnauzenorgan), dim lighting and abundant cover, excellent and stable water quality, and real caution with medications, since mormyrids as a group are notably sensitive to copper-based treatments and to poor water conditions.
Mormyrids also tend toward territorial aggression against their own kind, defending an individual space and an individual electric "signature" against conspecifics — a trait to bear in mind for any Gnathonemus species even in the absence of direct data for this one. Given how little is documented about G. echidnorhynchus specifically, it should not be assumed to behave identically to its relatives in every respect.
Conservation
The IUCN Red List assesses Gnathonemus echidnorhynchus as Least Concern, an assessment made on 16 February 2009. As a Congo-basin endemic restricted to the Kasai and Kwilu rivers and the middle Congo down to Wagenia Falls, its range is narrower than that of widespread mormyrids like G. petersii, but it is not currently considered threatened.
As with many Congo-basin river fishes, the main long-term pressures are generic rather than species-specific: habitat degradation, sedimentation and water-quality decline across the river system it inhabits. There is no evidence in the available sources of population decline or reassessment pressure for this species.