Taxonomy & naming
Petrocephalus longicapitis was described in 2012 by Bernd Kramer, Roger Bills, Paul Skelton and Michael Wink, in a critical revision of the genus Petrocephalus in southern and eastern Africa published in the Journal of Natural History. That single paper untangled several long-confused Zambezi-region populations, resurrected the name Petrocephalus tanensis, and described five species new to science — P. longicapitis among them. The genus belongs to the family Mormyridae, the elephantnoses and mormyrids, within Osteoglossiformes, the bonytongue fishes.
The type locality lies in the upper Zambezi River region of Namibia, where the holotype — 3.5 in in standard length — was collected. No older synonym attaches to the name; P. longicapitis was recognized as new in the 2012 revision rather than split out of a previously named species.
Morphology
Petrocephalus longicapitis reaches about 4.5 in standard length in the largest examined material; non-type specimens studied by Kramer and colleagues ranged from 1.5–4 in SL, bracketing the 3.5 in holotype. Like other members of the genus it has a compact, laterally compressed body, a blunt, rounded snout, and a small mouth, without the elongated chin barbel that marks the related genus Gnathonemus.
The feature behind its name is a markedly long head, measured at 25.8-29.6% of standard length in the type series — a proportion the original description used to separate P. longicapitis from superficially similar Petrocephalus sharing the upper Zambezi and Okavango drainages. As in all mormyrids, a weak electric organ in the caudal peduncle generates a pulse-type discharge used for orientation and communication in murky water; no species-specific discharge waveform has been published for P. longicapitis.
Habitat
Petrocephalus longicapitis is known from the upper and middle Zambezi River in Namibia and the Okavango system in Angola, part of the wider Zambezi River basin of south-central Africa. Within that range it favors quiet reaches — oxbow lakes and side-arms bordered by dense vegetation — alongside the sand-and-gravel-bottomed main channel, including stretches broken by rocky rapids.
By day the species shelters in what the original description terms marginal cover: holes in the riverbank, submerged root stocks, and beds of aquatic weed, a demersal, bottom-oriented habit typical of the genus. Water temperature and pH have not been published for this species specifically.
Feeding
No dietary study specific to Petrocephalus longicapitis has been published. As in other members of the genus, it is presumed to take small benthic invertebrates located by electrolocation among sand, gravel and submerged vegetation, but that presumption rests on the general pattern for Petrocephalus and Mormyridae rather than on direct observation of this species.
Mating
Courtship and mate recognition in Petrocephalus longicapitis have not been documented. In mormyrids generally, the electric organ discharge is thought to carry information relevant to species and sex recognition, and closely related, sympatric Petrocephalus are known to differ in their discharge waveforms — but no discharge recording or behavioral account has been published for this species, and extending the general pattern to it here would go beyond what is known.
Breeding
Breeding has not been recorded for Petrocephalus longicapitis, in the wild or in captivity. No spawning site, egg description, or account of parental care has been published for the species, and mormyrid reproduction as a whole remains poorly documented outside a handful of better-studied genera.
In the aquarium
Petrocephalus longicapitis has essentially no history in the aquarium hobby; it is not an established aquarium fish, and species-specific keeping accounts do not exist. General mormyrid husbandry would still apply were the species ever offered: a soft sand substrate for probing, dim lighting, ample cover such as driftwood and root tangles, and stable, low-turbidity water, since mormyrids as a group tolerate poor water quality and many common medications poorly. Live or frozen invertebrate foods offered after dark suit the family's nocturnal, electrolocation-driven foraging far better than daytime flake feeding.
Given how little is documented even about the wild diet and behavior of this species, any attempt at keeping it should be treated as experimental rather than routine.
Conservation
Petrocephalus longicapitis has not been evaluated by the IUCN Red List. FishBase characterizes the species as having high resilience — a minimum population doubling time under 15 months — and low vulnerability to fishing pressure, but that is a general life-history estimate rather than a conservation assessment. No population trend or species-specific threat has been documented.