Taxonomy & naming
Stomatorhinus fuliginosus was described by the Belgian ichthyologist Max Poll in 1941, in a paper on a fish collection from the Uele River in the Belgian Congo that also introduced two other new species. The type series consists of eight syntypes held at the Musée royal de l'Afrique centrale in Tervuren, Belgium, with the Uele River as the type locality.
The species belongs to the genus Stomatorhinus Gill, 1862, within the family Mormyridae — the elephantnoses and mormyrids — in the order Osteoglossiformes, the bonytongue fishes. Stomatorhinus is a genus of small, weakly electric mormyrids restricted to Central African river systems, and Stomatorhinus fuliginosus is one of thirteen currently recognized species in it. No synonyms are recorded for the name, and it is treated as valid in the standard fish catalogs.
Morphology
Stomatorhinus fuliginosus is a small fish, cited in general references at around 2 in, consistent with the genus as a whole — nearly all Stomatorhinus species stay under 4 in. A comparative study of a related species, S. ivindoensis, notes that S. fuliginosus is the only other described Stomatorhinus whose entire type series falls within that species' size range (syntypes up to about 2 in standard length), which places the type material in roughly that same small-bodied bracket.
As in other members of the genus, the mouth is small and set low on the underside of the head — the trait that gives Stomatorhinus its name — rather than extended into the elongated chin barbel seen in Gnathonemus and some other mormyrids. Like every mormyrid, S. fuliginosus carries a weak electric organ in the caudal peduncle, generating a low-voltage pulse discharge used for electrolocation and, presumably, communication; no electric organ discharge waveform has been published for this species specifically, though a broader anatomical survey has noted that Stomatorhinus as a genus has unusual electrosensory brain anatomy compared to other mormyrids.
Habitat
Stomatorhinus fuliginosus is known from the Congo River basin in the Democratic Republic of the Congo, with records spanning several of its central tributary systems, including the Kwango, Kasai, and Sangha drainages, in addition to the Uele River type locality in the northeast of the country. This places the species within the broad central African forest-and-savanna mosaic typical of the middle Congo basin.
No published data describe the specific water chemistry, temperature range, or substrate at any Stomatorhinus fuliginosus locality. Small mormyrids of this genus are generally associated with forest-stream and swamp habitat within the Congo system, but that expectation should not be read as measured data for this species — it remains, at present, undocumented.
Feeding
Diet has not been documented for Stomatorhinus fuliginosus specifically. A related congener, S. humilior, is reported to feed on vegetable debris, leaf litter, and the small invertebrate community associated with it, and mormyrids in general locate benthic prey by electrolocation, but neither observation has been confirmed for S. fuliginosus itself, and it would be a mistake to present it as established for this species.
Mating
No courtship or reproductive behavior has been published for Stomatorhinus fuliginosus. Mormyrids in general are thought to use their electric organ discharge in social and courtship signalling alongside its role in electrolocation, but this has not been studied or documented in this particular species.
Breeding
Breeding is unrecorded for Stomatorhinus fuliginosus. No spawning behavior, egg description, or parental-care account has been published, in the field or in captivity — consistent with the genus as a whole, whose reproductive biology is essentially unknown.
In the aquarium
Stomatorhinus fuliginosus has no documented history in the aquarium hobby and is not known to be traded. Almost everything published about it comes from the original 1941 description and later taxonomic comparisons with other Stomatorhinus species, not from husbandry.
Were a small mormyrid of this kind ever kept, general practice for the genus and family would apply: soft, sand-like substrate that a fish with a low, downturned mouth can probe without abrasion, dim lighting and ample cover to suit a species that likely relies on electrolocation more than eyesight, and live or frozen invertebrate foods rather than dry feed. Mormyrids as a group are known to be sensitive to poor water quality and to some common aquarium medications, so any hypothetical care regimen would need to start from that caution rather than from any track record specific to this species, which does not exist.
Conservation
The IUCN Red List assesses Stomatorhinus fuliginosus as Least Concern, in a 2022 assessment. No species-specific threats are detailed in the sources reviewed for this account; the assessment reflects the species' occurrence across several tributary systems of the central Congo basin rather than any documented population decline.