Taxonomy & naming
Petrocephalus cunganus was described by the Belgian-British ichthyologist George Albert Boulenger in 1910, from specimens collected in the Cunga area of the Cuanza (Kwanza) River in Angola — the source of the species name. It belongs to the family Mormyridae, the elephantnoses and mormyrids, within the order Osteoglossiformes. The order's common name, bonytongue, refers to a toothed bone on the floor of the mouth (the glossohyal) that bites against a toothed patch on the roof of the mouth, a jaw arrangement unique among living fishes and shared by a handful of otherwise very different families scattered across South America, Africa, Southeast Asia and Australasia.
The genus name Petrocephalus combines the Greek petros, "stone", and kephale, "head", referring to the thick, bony skull typical of the genus — these are small, deep-bodied mormyrids with a blunt, rounded head, quite different in profile from the long-snouted elephantnoses such as Gnathonemus. Petrocephalus is one of the larger mormyrid genera, with dozens of superficially similar species spread across African river systems, and many, including P. cunganus, are known mainly from the type series rather than from any body of subsequent field or aquarium observation.
Morphology
Petrocephalus cunganus is a small mormyrid, reaching about 4.3 in total length. Like other members of its genus it has a compact, laterally compressed body, a blunt, rounded head rather than the trunk-like snout of Gnathonemus, and a small, low-set mouth. FishBase describes the colouration as dorsal brown fading to a silvery ventral surface, the countershading pattern typical across the genus.
As in all mormyrids, the tail carries a weakly electric organ in the caudal peduncle, built from modified muscle tissue, which fires a pulse-type electric organ discharge. The waveform of this discharge is species-specific, and because many small Petrocephalus look almost identical to the eye, the discharge is often the most reliable character researchers use to tell one species from another. Mormyrids also have an unusually large cerebellum relative to body size, part of the neural machinery that processes the constant stream of electrosensory information the fish uses to read its surroundings.
Habitat
Petrocephalus cunganus is known only from the lower Cuanza (Kwanza) River system on the Atlantic coast of Angola, an isolated coastal drainage rather than part of the Congo or Zambezi systems that hold most other African mormyrids. The type locality, the Cunga area, gives the species its name. Records beyond the original collection are sparse; the IUCN assessment notes that subsequent surveys in Angola have not turned up further confirmed sightings.
No species-specific water-chemistry data have been published, so its exact temperature and pH range are not documented. Like other mormyrids of the region, it is presumed to live in dim, turbid, sediment-laden river water close to the bottom — the low-visibility conditions in which the electric sense is most useful — and the wider family typically occupies soft, mildly acidic, warm lowland river water around 75–82 °F.
Feeding
Specific dietary data for Petrocephalus cunganus have not been published. Mormyrids in general are benthic foragers, using their weak electric field to locate small invertebrates — insect larvae, worms and other soft-bodied prey — buried in sand or silt, usually feeding after dark or in the low-visibility water they favour. Given its blunt, rounded head, P. cunganus most likely takes similar prey from the riverbed rather than the more elongated-snout probing seen in genera such as Gnathonemus, but this is an inference from the family rather than a direct observation of the species.
Mating
No courtship or spawning behaviour has been documented for Petrocephalus cunganus. In mormyrids generally, the electric organ discharge is thought to play a role in courtship and species recognition — individuals appear to use differences in discharge waveform and pulse rate to pick out potential mates of their own species from among a crowd of superficially similar mormyrids — but how this translates into pairing and spawning is poorly worked out even in well-studied genera, and is not known at all for this species.
Breeding
Breeding in Petrocephalus cunganus is essentially unrecorded. Mormyrids as a family are seasonal, flood-triggered spawners in the wild, and captive breeding is rarely if ever achieved even for the handful of species that reach the aquarium trade in any numbers; this species, which is not established in the hobby at all, has no documented breeding record in captivity. Some mormyrids are thought to scatter eggs among plants with little further parental involvement, but that has not been confirmed for P. cunganus specifically.
In the aquarium
Petrocephalus cunganus is not a hobby fish. FishBase notes it is not commonly available in the aquarium trade, and given its Data Deficient status, uncertain wild population, and the absence of confirmed sightings since its original collection, there is no case for seeking it out. Discussion of care here is necessarily general, extrapolated from better-known mormyrids rather than the species itself.
Mormyrids as a group are demanding, specialist fish: they want soft, dim, tannin-stained water, are sensitive to poor water quality and to copper-based medications because of their electroreceptive skin, and often prove aggressive toward their own species in a confined tank, which argues for a single individual or a carefully spaced group rather than a crowd. None of this is a recommendation to keep P. cunganus — it is context for readers who encounter Petrocephalus or other small African elephantnoses in the trade under a similar-looking guise.
Conservation
The IUCN Red List classifies Petrocephalus cunganus as Data Deficient, an assessment made in 2007 and not updated since. The species is known only from the lower Cuanza River system in Angola, and the assessment notes that subsequent surveys in the region have not relocated it, leaving its current status, population size and trend unknown.
Data Deficient is not the same as safe: it means there is not enough information to assign a threat category, not that the species is secure. A single-river Angolan endemic with no confirmed records since its original description is a plausible candidate for future concern once targeted survey work establishes more about its status.