Taxonomy & naming
Petrocephalus longianalis was described in 2012 by Bernd Kramer, Roger Bills, Paul Skelton and Michael Wink, in a revision of the genus Petrocephalus published in the Journal of Natural History under the title "A critical revision of the churchill snoutfish, genus Petrocephalus Marcusen, 1854 (Actinopterygii: Teleostei: Mormyridae), from southern and eastern Africa, with the recognition of Petrocephalus tanensis, and the description of five new species." P. longianalis is one of those five new species. It belongs to Mormyridae, the elephantnoses and mormyrids, within Osteoglossiformes, the ancient bonytongue lineage of teleosts.
The type locality is Zambia, in the Luapula River system: the Lufubu River below Lufubu River Falls, at Chipili on the Mensa–Mununga road. The holotype is held at the South African Institute for Aquatic Biodiversity under catalogue number SAIAB 76758. No synonyms have been noted for the species since its description.
Morphology
Petrocephalus longianalis reaches about 4.5 in in standard length. It shares the family's general build — a laterally compressed, deep-bodied fish with a short, blunt, rock-hard cranium and a small mouth set low on the head, the source of the genus name Petrocephalus, "stone-head."
The describing revision recorded 22–26 soft dorsal rays and, notably, 30–35 soft anal rays, with the anal fin running 24.4–27.8% of standard length and the preanal length spanning 54.3–59.0% of standard length. That anal-ray count was the highest recorded among the Petrocephalus species compared in the study, making the long anal fin the species' clearest external diagnostic character. As in all mormyrids, an electric organ in the caudal peduncle generates a weak, pulse-type discharge used for orientation and communication; no species-specific discharge waveform has been published for P. longianalis, though electric organ discharge variation across Petrocephalus as a genus is generally smaller than that seen in other mormyrid subfamilies.
Habitat
Petrocephalus longianalis is known from the Luapula River system in Zambia, recorded from both the lower and upper sections of the drainage. The type locality — the Lufubu River below Lufubu River Falls near Chipili — is a braided, rocky channel running through dense riparian forest, with a rapid main flow broken by deep pools that provide slacker refuge water.
The substrate is predominantly rock, carrying considerable leaf litter, with sections covered by mats of aquatic water ferns, mosses and filamentous algae. The species is a demersal freshwater fish of tropical water; a specific temperature or pH range has not been published for it.
Feeding
No species-specific diet data has been published for Petrocephalus longianalis. Mormyrids in general, including other Petrocephalus species, are bottom-foraging invertebrate feeders that use electrolocation to find prey such as insect larvae, worms and small crustaceans hidden in sediment and leaf litter, but this has not been confirmed by direct observation or gut-content study for this species.
Mating
No courtship or mating behaviour has been published for Petrocephalus longianalis. Mormyrids are generally thought to use their species-specific electric organ discharge in social and reproductive signalling, but nothing beyond that general family pattern is documented for this species — it should not be assumed to apply here without direct study.
Breeding
Breeding has not been recorded for Petrocephalus longianalis, either in the wild or in captivity. No spawning account, egg description, or larval data has been published for the species.
In the aquarium
Petrocephalus longianalis has no documented presence in the aquarium hobby; it is not known to be traded or kept. Any account of husbandry would have to be extrapolated from mormyrids generally — soft substrate for probing, dim lighting and ample cover, stable water with minimal turbidity, live or frozen invertebrate foods offered after dark, and caution with medications, since mormyrids as a group are notably sensitive to poor water quality and some common treatments — but none of that has been tested against this species specifically, and it should not be presented as an established care record.
Conservation
Petrocephalus longianalis has not been evaluated by the IUCN Red List. No conservation assessment, population trend, or documented threat has been published for the species; it is known only from the Luapula River system in Zambia.