Taxonomy & naming
Petrocephalus similis was described by the ichthyologist Stéphane Lavoué in 2011, in a paper naming a new species of Petrocephalus from the Sanaga River basin of Cameroon, published in the journal Zootaxa (volume 2934, pages 20–28). It belongs to the family Mormyridae within Osteoglossiformes, the bonytongue fishes, and sits in the genus Petrocephalus Marcusen 1854, a group of several dozen small African mormyrids commonly called churchills. Eschmeyer's Catalog of Fishes lists no synonyms for the name.
The type locality is the Djerem River near Mbakaou Village, at approximately 6.21°N, 12.75°E, in the upper Sanaga basin of Adamaoua Province. The holotype is held at the Cornell University Museum of Vertebrates (CUMV 96318), with paratypes at the same institution (CUMV 93218, 93219, 93221) and at the Muséum national d'Histoire naturelle in Paris (MNHN 19789-0720). Lavoué placed the species in a small group of morphologically similar Central African Petrocephalus, distinguishing it from its closest relative, Petrocephalus sullivani, by a body lacking a melanin mark, 22–24 branched dorsal-fin rays, 28–29 branched anal-fin rays, a mouth commissure positioned under the posterior half of the eye, and a proportionally larger mouth and wider head.
Morphology
The largest recorded specimen measures 4.5 in in standard length, making Petrocephalus similis a small member of the family even by the modest standards of the genus. Like other Petrocephalus, it has the round-snouted, small-mouthed head typical of churchills, lacking the elongated chin barbel (schnauzenorgan) that characterizes the related genus Gnathonemus.
The features that separate it from its nearest relative, Petrocephalus sullivani, are subtle rather than obvious to the eye: an unmarked body without a melanin blotch, 22–24 branched dorsal-fin rays against 28–29 branched anal-fin rays, a mouth commissure that falls under the rear half of the eye, and a mouth and head that run proportionally larger and wider. As in every mormyrid, an electric organ near the base of the tail generates a weak, pulse-type discharge used for orientation and communication, but no waveform data or electrocyte study has been published for this species specifically.
Habitat
Petrocephalus similis is known only from the Djerem River, a tributary within the upper Sanaga River basin in Adamaoua Province, Cameroon, near Mbakaou Village. FishBase classifies it as a freshwater, benthopelagic species of tropical rivers. Lavoué's description places it within a species group of similar Petrocephalus restricted to Central Africa.
No temperature or water-chemistry data specific to this species has been published. The Djerem is a warm, tropical river system on the Adamaoua Plateau, but without measured figures for this population, any specific range would be a guess rather than a documented fact.
Feeding
FishBase records Petrocephalus similis as carnivorous, with an estimated trophic level of about 3.3, but no study has documented the specific prey items it takes in the Djerem River. Other Petrocephalus locate small benthic invertebrates by electrolocation before taking them with a quick strike of the small, downturned mouth, and this species likely feeds in a similar way, though that is an inference from the genus rather than a finding specific to this fish.
Mating
No courtship or spawning behavior has been published for Petrocephalus similis. Mormyrids in general are thought to use the electric organ discharge, alongside its role in navigation, as a signal in courtship and individual recognition, but nothing has been documented to confirm this for the species specifically — the electric discharge of this fish has not even been recorded, let alone studied for a behavioral role.
Breeding
Breeding is unrecorded for Petrocephalus similis. No spawning, maturity, or reproductive data has been published for this species, either from the wild or in captivity, and no aquarium account of it breeding exists.
In the aquarium
Petrocephalus similis has no documented presence in the aquarium hobby; it is known from taxonomic collections rather than the trade. A single-basin endemic first described from museum specimens in 2011, it is not a fish with any established care history to draw on.
What can be said follows from the family rather than from this species: mormyrids generally do best with a soft substrate for probing, dim lighting, ample cover, and stable water free of the pollutants and abrupt swings that this electrosensory group tolerates poorly. They are also known to be unusually sensitive to some common aquarium medications. None of that amounts to a care record for Petrocephalus similis itself, and anyone encountering a fish under this name should treat the identification with caution given how closely it resembles other Central African Petrocephalus.
Conservation
Petrocephalus similis has not been evaluated by the IUCN Red List. It is known only from its type locality on the Djerem River in the upper Sanaga basin, and no population or threat assessment has been published. A range this narrow would typically warrant conservation attention once assessed, but in the absence of a formal evaluation nothing can be said about its status beyond the fact that none exists.