Taxonomy & naming
The species was described by Albert Günther in 1867 as Mormyrus walkeri, in the Annals and Magazine of Natural History, from two syntypes collected in the Moyen-Ogooué region of the Ogooué River, Gabon (BMNH 1867.5.3.15 and 1867.5.3.16, measuring 3.5 in and 3.5 in standard length). It was moved into the genus Stomatorhinus when George Albert Boulenger erected that genus in 1898, and Stomatorhinus walkeri was later designated — by Jordan in 1920, as a subsequent rather than original type designation — as the type species of the genus.
Stomatorhinus sits in the family Mormyridae, the elephantnoses and mormyrids, within Osteoglossiformes, the ancient bonytongue lineage. Catalog of Fishes lists the species as valid, with its taxonomic history traced through later revisions by Taverne (1972), Gosse (1984), Poll & Gosse (1995), and more recent electric-organ-based work by Sullivan & Hopkins (2004), Hopkins et al. (2007), and Sullivan et al. (2016).
Morphology
Stomatorhinus walkeri is a small mormyrid, reaching about 3.5 in in total length, which is modest even by the standards of a genus made up almost entirely of fish under 4 in. Like other members of the genus it has an elongated, laterally compressed body and a small, inferior mouth set well back on the underside of a blunt snout, an arrangement suited to picking food items directly off or out of the substrate rather than grasping at midwater prey.
As in all mormyrids, a weak electric organ near the base of the tail generates a pulse discharge, read back through electroreceptors across the skin. Recorded discharges from S. walkeri last roughly 70 to 270 microseconds. Anatomically the genus is unusual: Stomatorhinus is reported to have only two zones in the electrosensory lateral line lobe of the brain, where every other mormyrid examined has three, a difference researchers have described as an outstanding puzzle in mormyrid brain evolution rather than a well-explained one.
Habitat
The species is known from the Ogooué River basin of Gabon, with its type locality in the Moyen-Ogooué region, and from the neighboring Niari-Kouilou basin of the Republic of Congo. Within the Ogooué system it appears to be the principal Stomatorhinus species of the main basin, and is notably absent from the upper Ivindo tributary, where a separate, allopatric species, S. ivindoensis, takes its place.
The Ogooué is a large tropical river system with substantial annual discharge — on the order of 4,2461 ft³/s where it has been gauged near Lambaréné — and a regional water temperature averaging around 81 °F. Published habitat data specific to S. walkeri, including its preferred depth, substrate, and the pH and conductivity of the water it occupies, has not been located; the figures above describe the wider river system rather than a measured microhabitat for this species.
Feeding
No species-specific dietary study of Stomatorhinus walkeri has been published. A related congener, S. humilior, is documented as a detritus feeder taking vegetable debris and leaf litter, and mormyrids as a family are typically bottom-foraging invertebrate feeders that locate prey by electrolocation in mud, silt, and leaf litter — but neither pattern has been confirmed directly for this species, and no captive feeding record exists to fill the gap.
Mating
Mormyrid electric organ discharge is thought, across the family, to carry information used in mate recognition and courtship alongside its role in orientation, and the unusual two-zone electrosensory lateral line lobe of Stomatorhinus suggests the genus processes this signal somewhat differently from its relatives — though what that means behaviorally for S. walkeri specifically has not been studied. Field collections of sexually mature specimens during the dry season hint at seasonal reproductive timing, but no courtship behavior, pairing, or signaling account for this species has been published.
Breeding
Breeding biology in Stomatorhinus walkeri is unrecorded. Spawning season, fecundity, egg or larval development, and any pattern of parental care are all absent from the available literature, and there is no report of the species being bred in captivity.
In the aquarium
Stomatorhinus walkeri has no established presence in the aquarium hobby; it is not a species with a documented captive-care history, and any account of keeping it would be extrapolation from mormyrids in general rather than lived experience with this fish. Mormyrids as a group are kept over soft, fine substrate that allows probing with the snout, with dim lighting and ample cover, and they are notably sensitive to poor water quality and to some common medications, which argues for cautious, gradual acclimation if a specimen is ever obtained.
At under 4 in this species would not be a size problem for most setups, but general mormyrid husbandry favors either a single specimen with calm, non-nipping tankmates or an established group large enough to spread out territorial behavior, since a lone pair often fares poorly. None of this has been verified for S. walkeri itself, and it should be read as general guidance for the genus rather than a track record for the species.
Conservation
The IUCN Red List assessed Stomatorhinus walkeri as Least Concern on 16 February 2009. The assessment reflects a species known from more than one river basin in Gabon and the Republic of Congo without evidence of a significant range-wide decline; no species-specific threats are detailed in the available sources.