Taxonomy & naming
Petrocephalus soudanensis was described by Régine Bigorne and Didier Paugy in 1990, in Lévêque, Paugy & Teugels's Faune des poissons d'eaux douces et saumâtres de l'Afrique de l'Ouest (Fauna of freshwater and brackish fishes of West Africa). The type locality is the Niandan River at Loutou, Guinea, and the holotype is held at the Muséum national d'Histoire naturelle in Paris (MNHN 1990-0139). It belongs to the family Mormyridae, subfamily Petrocephalinae, within Osteoglossiformes, the ancient bonytongue lineage of teleosts; the Catalog of Fishes lists it as a valid species with no recorded synonyms.
The genus Petrocephalus groups several dozen small, round-snouted African mormyrids sometimes called churchills, set apart from genera such as Gnathonemus by the absence of an elongated, trunk-like chin appendage. Many Petrocephalus species are difficult to tell apart by external appearance alone, and later genus-wide revisions have leaned on the electric organ discharge — the waveform each species produces — as a more reliable diagnostic character than color pattern or fin shape.
Morphology
Petrocephalus soudanensis is a small mormyrid, reaching about 4.5 in in total length according to FishBase. Like other Petrocephalus species it has a compact, laterally compressed body, a blunt, well-rounded snout, and a small mouth set low on the head — a plain, silvery fish next to the trunk-nosed Gnathonemus species that dominate the mormyrid side of the aquarium trade.
As in all mormyrids, an electric organ near the base of the tail generates a weak, pulsed field that the fish reads through electroreceptors spread across its skin, using the signal to navigate and to locate prey in turbid or low-light water. A study of Petrocephalus species from the Volta system, part of this species' range, found the discharge in that fauna to be short and triphasic (three-phase). Because many Petrocephalus species look almost identical externally, the waveform of the discharge — rather than appearance — has become the more dependable way to separate similar species in the genus.
Habitat
Petrocephalus soudanensis is known from river systems across the West African Sudanian belt: the upper and lower Niger, the upper Benue, coastal drainages of Nigeria, the Volta basin, and the Chad basin. The type locality is the Niandan River at Loutou in Guinea, part of the upper Niger system, and the species has also been recorded from the Baoulé River within the Niger basin in Mali.
Within these rivers it is demersal, living near the bottom over bare stone, rock, and other hard substrates such as oyster banks rather than soft sediment or dense vegetation. Specific temperature and pH data have not been published for this species. West African Sudanian-belt rivers of this kind are typically warm, seasonally fluctuating systems shaped by a single annual flood pulse, but that is a general expectation for the region rather than a measurement taken for P. soudanensis.
Feeding
No dedicated dietary study has been published for Petrocephalus soudanensis. FishBase places it at a trophic level of about 3.2, consistent with a mid-level invertebrate predator rather than a specialist feeder. By analogy with better-studied congeners, which take chironomid (midge) larvae, mayfly and caddisfly larvae, and dragonfly and damselfly nymphs from the riverbed, P. soudanensis is presumed to forage on similar benthic invertebrates over its hard-substrate habitat, located by electrolocation rather than by sight. No feeding record specific to this species in captivity is documented.
Mating
Courtship or mate-recognition behavior has not been documented for Petrocephalus soudanensis specifically. In mormyrids generally, the electric organ discharge is thought to carry information relevant to species and sex recognition and to shoal cohesion. A study of Petrocephalus species from the Volta system, part of this species' range, found no consistent difference in discharge waveform between males and females, so the signal appears to separate species from one another more reliably than it separates sexes within a species. External physical differences between the sexes are recognized in the genus in general terms but have not been specifically described for P. soudanensis.
Breeding
Detailed field or captive breeding accounts specific to Petrocephalus soudanensis are not published. FishBase reproduction data for the species describe adhesive eggs about 0.5 in in diameter, fecundity in the range of hundreds to thousands of eggs per female, and a seasonal spawning pattern tied to the rains, with external fertilization delivered in fractional bouts rather than a single event; no nest-building or parental guarding is reported.
FishBase also notes that spawning has been achieved in captivity by simulating flood conditions, though no further detail — researcher, location, or year — accompanies that record, and it reads as a research account rather than an aquarium-hobby one. No hobbyist reports of breeding P. soudanensis in a home aquarium are known, and the species has essentially no track record in the trade.
In the aquarium
Petrocephalus soudanensis is essentially unknown in the aquarium trade. It is not a species hobbyists are likely to encounter, and no established care tradition exists for it outside the research account noted above. Any fish sold under this name should be treated with caution, since Petrocephalus species are notoriously difficult to distinguish without examining the electric organ discharge, and misidentification within the genus is common.
Were it kept, general mormyrid husbandry would apply: a soft sand substrate suited to a bottom-oriented, electrolocating fish, dim lighting, and ample cover such as roots or driftwood to reduce stress. Mormyrids as a group feed poorly on dried foods and do best on live or frozen invertebrate foods such as bloodworm and brine shrimp, and they are well known for sensitivity to poor water quality and to some common aquarium medications — gradual acclimation and conservative dosing are standard precautions for the family rather than anything specific to this species.
Conservation
The IUCN Red List assesses Petrocephalus soudanensis as Least Concern, based on an assessment dated June 4, 2019. It is documented across a broad span of West African river systems, from the upper Niger to the Chad basin, with high estimated population resilience — a minimum population doubling time of under 15 months — and low vulnerability to fishing pressure. No species-specific threats are identified in the assessment; general pressures on Sudanian-belt rivers, such as damming, siltation, and declining water quality, are long-term concerns for West African river fishes broadly, but they are not flagged as acting on this species in particular.