Taxonomy & naming
Petrocephalus leo was described by Sébastien Lavoué in 2016, in a Zootaxa paper on new African electric fish from the Oubangui River basin, part of the Congo system. It belongs to Mormyridae, the elephantnoses and mormyrids, within Osteoglossiformes — the ancient bonytongue lineage of teleosts, named for a bony, toothed structure on the tongue that bites against toothed plates on the roof of the mouth. Within the family it sits in Petrocephalus, the churchills: small, round-snouted mormyrids that lack the elongated chin appendage, the schnauzenorgan, carried by their better-known relative Gnathonemus. No subgenus has been assigned to it in the published literature.
The type locality is the Kotto River at Mingala (5.10°N, 21.82°E), a right-bank tributary of the Oubangui in Basse-Kotto Province, Central African Republic, where the type series was collected in March 2006. The holotype, CUMV 95314, is a 3 in SL male held at the Cornell University Museum of Vertebrates; three paratypes are held at the Royal Museum for Central Africa in Tervuren. No synonyms exist — Petrocephalus leo has been recognized as valid since its description. A later molecular study found that its mitochondrial cytochrome b haplotypes were nested within those of the separate species Petrocephalus zakoni, while a nuclear marker, the S7 ribosomal protein intron, supported the two as reciprocally monophyletic — the first documented case of this kind of mitochondrial–morphological conflict reported within the genus.
Morphology
Petrocephalus leo is a small mormyrid, reaching about 3 in in standard length, which places it toward the smaller end of a genus made up mostly of modest-sized fish. Like other churchills it has the round, blunt snout and short, deep-bodied outline typical of the group, without the elongated tubular chin found in Gnathonemus.
The original description separates it from close relatives chiefly on pigmentation: Petrocephalus leo carries a black mark at the base of the pectoral fins but lacks the subdorsal black blotch present in many congeners, giving it a distinctive melanin pattern. Unusually for the genus, it also lacks the electroreceptive rosettes scattered over the head in most Petrocephalus species, a feature reported as unique to this species within the genus. As in all mormyrids, an electric organ near the base of the tail generates a weak, pulsed discharge used for electrolocation and communication; no waveform or discharge-rate data specific to Petrocephalus leo have been published.
Habitat
Petrocephalus leo is known only from the lower Oubangui (Ubangui) River system in the Central African Republic, part of the middle Congo River basin. It has been recorded from the Kotto River — a right-bank tributary of the Oubangui, in Basse-Kotto Province — as well as from the Ouaka River and the Oubangui itself at Bangui.
FishBase classifies it as a benthopelagic freshwater fish of tropical freshwater systems. No published data describe the temperature, pH, or other water chemistry of the rivers it inhabits, and the species is best treated as a Congo-basin river fish of ordinary tropical conditions rather than one with documented, specific requirements.
Feeding
No dietary study has been published for Petrocephalus leo. Mormyrids in general, including other Petrocephalus species, forage on small benthic invertebrates — insect larvae, worms, and tiny crustaceans — located by electrolocation in mud and submerged debris, but this pattern has not been confirmed specifically for this species. Nothing is documented about its feeding in captivity, since it is not known to be kept.
Mating
No courtship or mate-recognition behaviour has been described for Petrocephalus leo. In mormyrids generally, the electric organ discharge is species- and often sex-specific and is thought to play a role in recognizing potential mates, but whether that holds here cannot be said — no discharge waveform has even been recorded for this species, let alone its behavioural use.
Breeding
Breeding has not been recorded for Petrocephalus leo, in the wild or in captivity. The species was described only in 2016 from a small type series, and no subsequent study appears to have examined its reproduction. Nothing about spawning behaviour, fecundity, or parental care can be stated with any confidence.
In the aquarium
Petrocephalus leo has no known history in the aquarium hobby. It is a recently described, narrow-range species from a small stretch of the Oubangui system, and there is no record of it having been collected for the trade or kept in captivity. General mormyrid husbandry would apply if it ever became available: a soft substrate for probing, dim lighting, and ample cover, with live or frozen invertebrate foods rather than flake, since mormyrids as a group are notably sensitive to poor water quality and to many common medications. None of this comes from an actual keeping record for this species, and it should be read as general guidance for the genus rather than an account of Petrocephalus leo in an aquarium.
Conservation
Petrocephalus leo has not been evaluated by the IUCN Red List. It is known only from a handful of localities in the lower Oubangui drainage of the Central African Republic — the Kotto River near Mingala, the Ouaka River, and the Oubangui at Bangui — and no data on population size or trend have been published. Its conservation status is simply unknown.