Taxonomy & naming
Stomatorhinus ater was described by the French ichthyologist Jacques Pellegrin in 1924. Pellegrin, based for most of his career at the Muséum national d'Histoire naturelle in Paris, described a large number of Central African freshwater fishes from museum material assembled during the colonial period, and Stomatorhinus ater is one of many small mormyrids that passed through his hands during that work. The species is placed in the family Mormyridae within the order Osteoglossiformes, the bonytongues — an ancient teleost lineage found today on four continents and united by a toothed bone on the tongue that bites against a toothed plate on the roof of the mouth.
The genus Stomatorhinus was erected by George Albert Boulenger in 1898 for Stomatorhinus corneti, a small Congo basin mormyrid distinguished from most of its relatives by a small mouth set low and close to the tip of a short, rounded snout, rather than tucked beneath a fleshy chin barbel as in Gnathonemus or drawn out into an elongated, downcurved tube as in Campylomormyrus and some Mormyrus. The genus now holds more than a dozen recognized species, nearly all of them narrow-range Congo basin endemics, with a handful of relatives known from the neighboring Ogooué system in Gabon. A confirmed type locality for Stomatorhinus ater specifically was not found in the sources reviewed for this account, and the species does not appear to have been the subject of a modern taxonomic revision.
Morphology
Stomatorhinus ater follows the general body plan of its genus: a small, elongated, laterally compressed body with a single dorsal fin set back over a similarly placed anal fin, and the small, low-set mouth near the tip of the snout that gives the genus its name. Species-specific measurements are not documented in the sources reviewed for this account. Congeners in the genus are mostly small mormyrids well under 4 in standard length, and nothing in the available literature suggests this species departs markedly from that range.
As in every mormyrid, an electric organ near the base of the tail generates a weak, pulse-type discharge, read back through electroreceptors spread across the skin. That electrosense lets the fish navigate and locate prey in turbid or nighttime water where eyesight is of limited use, and it is associated with a brain-to-body mass ratio among the highest recorded in any vertebrate, built around an enlarged cerebellum devoted to processing the electrosensory stream. In Stomatorhinus, as in many small mormyrid genera, the discharge waveform is often a more reliable way to separate similar-looking species than external coloration or fin counts, but no electric organ discharge recording specific to Stomatorhinus ater has been published.
Habitat
As a member of Stomatorhinus, Stomatorhinus ater is necessarily an African freshwater fish, and the genus as a whole is centered on the Congo River basin in Central Africa, with a few relatives extending into the adjoining Ogooué system in Gabon. A confirmed locality record — the specific river, tributary, or country — for Stomatorhinus ater itself was not found in the sources reviewed for this account, and its precise range should be treated as unconfirmed rather than assumed from the genus alone.
General Mormyridae habitat across the Congo basin runs to warm, turbid, often tannin-stained lowland rivers, forest streams, and floodplain margins with cover from submerged wood and root tangles — low-visibility conditions in which an electric sense outperforms eyesight. That broad family and genus picture is the best available guide to where Stomatorhinus ater most likely lives, but it is not a measured or documented habitat description for this particular species.
Feeding
No species-specific feeding study exists for Stomatorhinus ater. Mormyrids in general, and the small-mouthed Stomatorhinus in particular, are understood to be benthic invertebrate feeders that use electrolocation to find insect larvae, worms, and small crustaceans hidden in mud, sand, and leaf litter, taking them with a quick strike of the small mouth. That general feeding mode is the best available description of how this species most likely forages, in the absence of any direct observation.
The species has no documented presence in the aquarium trade, so there is no body of hobbyist feeding experience to draw on either; care notes for it would have to be extrapolated from better-studied small mormyrids such as Petrocephalus rather than reported directly.
Mating
Nothing has been published on courtship or mate choice in Stomatorhinus ater specifically. In mormyrids generally, the electric organ discharge is thought to carry more than navigational information — its waveform is often species- and sex-specific, and general reviews of mormyrid biology propose it plays a role in mate recognition and courtship signalling alongside shoal cohesion. Whether that holds for this species has not been tested.
Given the complete absence of field or aquarium observation, any account of pairing behavior, seasonal timing, or signalling specific to Stomatorhinus ater would be speculation rather than a reported fact.
Breeding
Breeding has not been recorded for Stomatorhinus ater, in the wild or in captivity. That gap matches the family as a whole: mormyrid reproduction is poorly studied outside a handful of well-observed species, and almost none have been bred under aquarium conditions.
Where mormyrid breeding has been documented at all, it tends to follow seasonal flooding, with eggs scattered among submerged vegetation and little or no parental care afterward. Whether that pattern applies to Stomatorhinus ater is not known, and it should be read as a reasonable extrapolation from relatives rather than a documented fact for this species.
In the aquarium
Stomatorhinus ater has no documented presence in the aquarium trade. Small mormyrids in genera such as Stomatorhinus and Petrocephalus are frequently sold under generic labels such as "elephantnose" with little regard for species identity, and any fish offered under this name should be treated with real skepticism given how similar many small mormyrids look to one another.
Where general Mormyridae husbandry would apply — should a specimen ever appear in the trade — it calls for a soft sand substrate rather than sharp gravel, since the skin carries electroreceptors that are easily damaged, along with dim lighting, secure cover, and stable, clean water; the family as a whole is notably intolerant of ammonia and nitrite and unusually sensitive to copper-based and some other common medications. Congeners in the genus are small, well under 4 in, so size is unlikely to be an obstacle, but without a confirmed care record for this species specifically, any attempt at keeping it would rely almost entirely on general mormyrid experience rather than documented practice.
Conservation
Stomatorhinus ater has not been evaluated by the IUCN Red List. Its status should be treated as genuinely unknown rather than assumed safe, a common situation among the more obscure members of a large, taxonomically difficult family with patchy survey coverage across Central Africa.
Without a confirmed range, no threat specific to this species can be identified. Congo basin freshwater fish in general face pressures from habitat degradation, sedimentation, and water-quality decline linked to deforestation, agriculture, and development across the basin, and any of these could bear on Stomatorhinus ater once its distribution is better documented.