Taxonomy & naming
Pelmatochromis ocellifer was described by the Belgian-British ichthyologist George Albert Boulenger in 1899, in the Proceedings of the Zoological Society of London, on a single fish collected by the missionary Reverend John H. Weeks at Monsembé on the upper (middle) Congo River. That specimen — total length about 5 in — remains the unique holotype, held in the Natural History Museum, London under register BMNH 1898.7.9.16; Monsembé is the type locality. Boulenger placed the fish directly in Pelmatochromis, a genus erected by Franz Steindachner in 1894, and redescribed it at greater length in his monographs on the fishes of the Congo (1901) and in his Catalogue of the Fresh-water Fishes of Africa (1915). The genus sits in the subfamily Pseudocrenilabrinae, the great African cichlid radiation. Over the twentieth century Pelmatochromis was a taxonomic catch-all into which many West and Central African cichlids were dumped, and most have since been moved out to genera such as Pelvicachromis, Pterochromis, Chromidotilapia and the tilapiine Pelmatolapia; the modern, narrowly-defined Pelmatochromis is a small genus of just a handful of species. Pelmatochromis ocellifer was for a time confused with the West African P. buettikoferi — Pellegrin (1904) treated specimens of it under that name — but the two are distinct, and the validity of Pelmatochromis ocellifer has been upheld in the standard checklists (Daget 1991; Stiassny, Teugels & Hopkins 2007; Fermon et al. 2022). Catalog of Fishes and FishBase both list it as a valid species confined to the middle Congo.
Morphology
This is a modest-sized, fairly typical Pelmatochromis in build — a moderately deep-bodied, laterally compressed cichlid with the depth of the body going about two and a quarter to two and a half times into the total length, and a head nearly twice as long as it is broad. The largest specimen Boulenger measured was 5 in (5 in) total length, and FishBase carries the same 5 in figure as the maximum. The snout is rounded with a straight or slightly concave upper profile; the eye is large, going roughly three and a half to four and a half times into the head length. The fin counts run to about XIV–XV spines and 10–12 soft rays in the dorsal and III spines with 8–9 soft rays in the anal, with the longest dorsal spines toward the rear of the spiny portion and the middle soft dorsal rays drawn out — in adults the produced soft rays reach about the length of the head, and the pelvic (ventral) fins extend into filaments that reach past the start of the anal fin. There are 27–29 scales in a longitudinal series. In life the body is a plain brownish above, paler below, marked with about five rather indistinct dark vertical bars that may break up into a row of dark blotches along the flank; there is a black blotch on the gill cover. The diagnostic feature, and the source of the name, is a dark ocellus — a rounded spot, frequently rimmed with a lighter halo — set at the base of the dorsal fin at the junction of the spiny and soft portions, while the soft dorsal itself is sprinkled with small light spots. Sexual dimorphism in the genus follows the usual cichlid pattern of males growing larger and developing longer trailing fin filaments, but the dimorphism of this particular species has not been formally documented from any series of wild fish.
Habitat
Pelmatochromis ocellifer is a freshwater, bottom-associated (demersal) fish of the middle Congo River basin in Central Africa. FishBase maps its range from Pool Malebo (Stanley Pool, the broad lake-like reach of the Congo above Kinshasa and Brazzaville) upstream to the Yangambi area, taking in several right-bank and tributary systems — the Mongala, the Itimbiri, the Aruwimi, and the Dja. The Catalog of Fishes restricts the confirmed range to the Democratic Republic of the Congo; the IUCN assessment additionally lists the Republic of the Congo and the Central African Republic within the basin. Older records of the species from Lower Guinea (the coastal rivers of southern Cameroon and Gabon) are now regarded as misidentifications of its western relative Pelmatochromis nigrofasciatus, so the species is best treated as a middle-Congo endemic. No in-situ water chemistry has been published specifically for this fish, but the middle Congo and its forest tributaries are characteristically warm, soft and slightly acidic to near-neutral blackwater and clearwater; FishBase gives a tropical temperature preference of about 77–82 °F. As a small demersal cichlid it would be expected in the shallow margins, among submerged wood, leaf litter and root tangles, of these lowland forest rivers; a working depth band of roughly 0–16 ft fits the shoreline-and-shallows habit of the genus, though no measured depth range exists for the species itself.
Feeding
No direct dietary study of Pelmatochromis ocellifer has been published, and FishBase carries no examined gut contents for it; the trophic level of about 3.3 listed there is an estimate derived from its size and from the diets of its closest relatives rather than from analysis of this fish. Within the genus, Pelmatochromis are small benthic foragers with the multi-row jaw dentition (the species shows three to five series of teeth) and short, broad gill rakers typical of generalist omnivores that pick small invertebrates, insect larvae, crustaceans and other benthic prey from the substrate and from among submerged wood and leaf litter, supplementing this with algae and organic detritus. On the available evidence it is best described as a small benthic omnivore of the river-margin community, neither a specialised piscivore nor a dedicated herbivore.
Mating
The courtship and pairing behaviour of Pelmatochromis ocellifer specifically has not been recorded — like much of its biology, it is simply unstudied in the wild and essentially unkept in captivity. What can be said is drawn from the genus and its close West-and-Central-African substrate-spawning allies (Pelmatochromis, Pelvicachromis, Chromidotilapia and their relatives), which are overwhelmingly monogamous, pair-bonding cichlids. In these fish a male and female form a bond, jointly select and clean a spawning site — typically a cave, crevice or sheltered hollow under wood or stone — and defend a territory around it together through a courtship that involves mutual displaying, with the developing colours and the produced fin filaments of the male serving as signals. By analogy Pelmatochromis ocellifer is expected to be a territorial pair-spawner rather than a harem-forming or open-water species, but this should be read as a genus-typical inference, not a documented observation for this particular fish.
Breeding
There is no published account of Pelmatochromis ocellifer spawning, in the wild or in an aquarium — fecundity, egg number, egg size and larval development are all unrecorded for the species, and FishBase lists no reproductive data. The reasonable inference, drawn from the genus and its substrate-spawning relatives, is that it is a biparental cave (substrate) spawner: a bonded pair lays a clutch of adhesive eggs on the roof or wall of a sheltered cavity, the female tending and fanning the eggs while both parents guard the site, and the pair continuing to shepherd the free-swimming fry for a period after hatching. Clutch size for small cichlids of this guild is typically on the order of a few dozen to a couple of hundred eggs (genus-typical, not measured for this species). Until someone collects and breeds the fish, every specific figure for its reproduction remains genuinely unknown, and it would be wrong to present otherwise.
In the aquarium
Pelmatochromis ocellifer is, for practical purposes, not an aquarium fish. It is essentially absent from the ornamental trade: it is not bred commercially, it does not appear in hobby stocklists, and there is no body of keeper experience or care literature for it — searches for husbandry information return results for unrelated cichlids rather than for this species. Anyone who did obtain wild-collected specimens would have to extrapolate from the requirements of its better-known relatives. That would mean a warm, soft-water set-up reflecting the middle-Congo forest rivers it comes from: temperatures around 77–82 °F, a pH in the soft acidic-to-neutral range (roughly 6.0–7.5), and gentle filtration. For a 5 in substrate-spawning cichlid a modestly sized aquarium of at least around 25–30 US gal would be a sensible minimum for a pair, furnished as for its cave-spawning kin — a soft or sandy bottom, plenty of cover in the form of bogwood, leaf litter, roots and at least one or two enclosed caves or upturned shelters to serve as potential spawning sites and as refuges that let a subordinate fish escape an aggressive mate. Diet would be the usual varied menu for a small omnivorous cichlid: live and frozen invertebrates (bloodworm, brine shrimp, small crustaceans) alongside good-quality prepared foods. As with most pair-bonding cave spawners, the main behavioural caution is territorial aggression around breeding, which a larger tank and broken sightlines help to manage. All of this is informed guesswork by analogy, not established practice — it should be treated as such.
Conservation
The IUCN Red List assesses Pelmatochromis ocellifer as Data Deficient (DD), assessed on 16 February 2009 by T. Moelants, with the population trend listed as unknown. The Data Deficient category reflects exactly the situation described throughout this account: the species is known from very few records, its distribution within the middle Congo is imperfectly mapped, and there is essentially no information on its population size, ecology or any threats it may face — too little, in the assessors' judgement, to place it in any of the threatened or non-threatened categories. It carries no CITES listing and is of no fisheries importance. The species is not known to be the target of any specific pressure, but the broader middle Congo basin faces the familiar regional stresses of deforestation in its catchment, expanding artisanal and small-scale fisheries, pollution near growing river towns, and the prospect of hydropower development on the main river — diffuse pressures that form the backdrop to the species' status rather than any documented decline. The clear conservation priority for this fish is simply basic fieldwork: until it is collected and studied again, its true range, abundance and vulnerability cannot be judged.