Taxonomy & naming
The species was described by the Belgian-British ichthyologist George Albert Boulenger in 1899 as Tilapia lepidura, in his revision of the African and Syrian Cichlidae published in the Proceedings of the Zoological Society of London. The type locality is given simply as "Angola." The name long sat within the sprawling, polyphyletic genus Tilapia, and a string of early-twentieth-century workers — Boulenger himself in his 1915 Catalogue of the fresh-water fishes of Africa, Pellegrin, Nichols & Griscom, and later Thys van den Audenaerde in his revisions of the Congolese Tilapia — all treated it under that name. The modern placement comes from Ethelwynn Trewavas's landmark 1983 monograph, Tilapiine fishes of the genera Sarotherodon, Oreochromis and Danakilia (British Museum (Natural History)), which split the maternal mouthbrooders into Oreochromis and assigned lepidurus there, within the subgenus Nyasalapia (her fig. 145). The original material was fixed by Trewavas & Teugels in 1991, who designated the lectotype BMNH 1873.7.28.8, with a paralectotype (BMNH 1887.1.13.5) from the Lower Congo. Eschmeyer's Catalog of Fishes lists the species as valid as Oreochromis lepidurus (Boulenger 1899), in the cichlid subfamily Pseudocrenilabrinae, while noting that at least one recent regional treatment (Fermon et al. 2022) flags its status with a question mark — a reflection of how thinly the fish has been collected and how little fresh material exists to anchor its limits.
Morphology
Oreochromis lepidurus is a small, deep-bodied, laterally compressed tilapia. FishBase gives a maximum total length of about 7.5 in, and museum material runs smaller still — the CLOFFA database cites a specimen of roughly 5.5 in standard length — so this is a modest fish by the standards of a genus that includes half-metre food-fishes. The fin counts are typical of the genus: 15 to 17 dorsal spines and 9 to 12 dorsal soft rays, three anal spines with 8 to 9 soft rays, and 28 vertebrae. Trewavas's diagnosis emphasised a long snout, a deep preorbital bone, and a robust lower pharyngeal jaw whose toothed blade runs 2 to 2.3 times the length of the dentigerous area; the outer jaw teeth are bicuspid unless the minor cusp has worn away, and there are roughly 19 to 24 rakers on the lower limb of the first gill arch. The diagnostic feature that gives the species its name is the caudal fin: in adults it is densely covered in small scales, usually overlying a reticulate pattern of dark melanin — "scaly tail," lepidurus. Sexual dimorphism is expressed at the genital papilla rather than in dramatic colour: mature males carry a tuberculate genital papilla, some of whose tubercles are drawn out into short filaments. Live coloration is poorly documented; the species has rarely if ever been photographed alive, and FishBase carries only a generic line drawing in its place.
Habitat
The species is endemic to the lower Congo River system. FishBase records it from the lower Congo basin in the Democratic Republic of the Congo, with additional reports from Angola, where it is thought to occur in the lower Congo proper and in the coastal rivers running between the Congo mouth and the Bengo. (A scattering of database entries extending the range to the Athi, Tana and Jubba rivers of Kenya and Somalia appears to be a transcription error confounding lepidurus with the East African Oreochromis spilurus complex; every primary source — Boulenger's Angolan type, Trewavas's monograph, and the IUCN assessment — restricts the species to the lower Congo and Angola, and that is the range followed here.) This is a demanding place to live. The Lower Congo Rapids ecoregion sees the river fall some 919 ft over 217 mi between the foot of Malebo Pool and Matadi, alternating between narrow gorges barely 656 ft across and wider braided stretches, with 32 named falls and rapids; the fish fauna here is famously specialised for fast water, and a third of its species are endemic. Oreochromis lepidurus, a plankton-feeder, is a fish of the calmer pools and backwaters between the cataracts and of the adjacent Malebo Pool wetlands rather than of the rapids themselves. The IUCN classifies its habitat simply as inland wetlands. In-situ chemistry has not been published for this species specifically, but the lower Congo and its Angolan coastal-river neighbours are warm, soft, generally circumneutral tropical waters; FishBase records it as freshwater and brackish-tolerant and benthopelagic, consistent with a fish that ranges from river backwaters toward the lower, slightly saline reaches.
Feeding
Oreochromis lepidurus is a microphagous planktivore. Trewavas characterised it as feeding on plankton, and FishBase repeats the description: the fish strains fine suspended food rather than grazing algal turf from rock like some of its rift-lake relatives or sieving sediment like the eartheaters of South America. The long, fairly numerous gill rakers (around 19 to 24 on the lower limb) are the apparatus for this — a filtering comb that retains phytoplankton, small zooplankton and suspended detritus drawn in with the water. The robust lower pharyngeal jaw, with its long toothed blade, then mills whatever is gathered. As a small plankton-sifter occupying the calmer water of a turbulent river, it sits low on the food web and would have functioned as a link between the suspended primary production of the pools and the larger predatory fishes and birds of the lower Congo — though, as with much of this fish's biology, direct dietary study in the wild is essentially absent and the trophic picture is inferred from morphology and Trewavas's brief notes.
Mating
Like all Oreochromis, Oreochromis lepidurus is a maternal mouthbrooder, and the genus's reproductive template implies a lek-style mating system in which males, not pairs, hold the territories. Across the genus, ripe males establish and defend a spawning site — typically a cleared pit or scrape on the bottom — and display to passing females, which visit only to spawn before withdrawing to brood the clutch alone. The one piece of species-specific evidence that bears on this is the male's tuberculate genital papilla with its filamentous tubercles, a structure used in the close-quarters courtship and gamete transfer that characterise tilapiine spawning. The detailed courtship of Oreochromis lepidurus — pit construction, male coloration in nuptial dress, the choreography of the spawning pass — has not been described from the wild or from captivity, and is assumed to follow the well-documented Oreochromis pattern rather than being known in its own right.
Breeding
Oreochromis lepidurus is documented as a maternal, ovophilic mouthbrooder: the female takes the fertilised eggs into her mouth immediately after spawning and incubates them there, and after hatching the larvae and early fry continue to shelter in the buccal cavity, bolting back to it when threatened. This is the defining reproductive strategy of the genus and removes the brood almost entirely from the reach of the egg- and fry-predators that crowd a tropical river. Specific figures for this species — clutch size, egg diameter, the duration of incubation, the size at release — have not been published; they have simply never been recorded. As a genus-typical guide, Oreochromis females of comparable body size brood on the order of tens to a few hundred eggs per spawning (small species sometimes well under a hundred), with parental care provided by the female alone and no male involvement after fertilisation. Until Oreochromis lepidurus is bred or observed spawning, those genus-level expectations are the best that can be offered for it, and they should be read as such rather than as measurements of this fish.
In the aquarium
Oreochromis lepidurus is not an aquarium fish in any meaningful sense. It is absent from the ornamental trade, has no established common name, and is not figured live in the standard databases; FishBase carries no aquarium-maintenance record for it. There is no body of hobbyist husbandry to report, and it would be dishonest to manufacture one. Any keeping notes can only be extrapolated from the genus, and even then with caution given the species' Endangered status and its restriction to a single threatened river system. Should wild or research stock ever be held, the general requirements of a small riverine Oreochromis would apply: a long, well-filtered tank with a sand or fine-gravel bottom and open swimming water, warm tropical temperatures in roughly the 73–82 °F band, soft to moderately hard water around neutral pH (about 6.0–7.5), and a finely divided, plankton-substitute diet — quality powdered and small flake foods, spirulina-based preparations, and live or frozen micro-foods such as Artemia nauplii and Daphnia — to suit a filter-feeding mouth. Tilapiine mouthbrooders are typically robust and adaptable, but males become territorial when in breeding condition, so space and line-of-sight breaks matter. None of this should be taken as a recommendation to seek the fish out: it is a conservation-sensitive endemic, not a candidate for the hobby.
Conservation
The IUCN Red List assesses Oreochromis lepidurus as Endangered, under criteria B1ab(iii)+2ab(iii) — a small and fragmented range together with a continuing decline in habitat quality. The assessment was carried out by T. Moelants on 16 February 2009 and published in 2010, and the species remains listed as Endangered in the current Red List version; the population trend is recorded as unknown. The listed threats are characteristic of the lower Congo: mining and quarrying, the busy shipping lanes of the Matadi–Kinshasa corridor, dams and water-management works, and industrial and military effluents, all bearing on a fish with a naturally restricted distribution. The Lower Congo Rapids and Malebo Pool ecoregions in which it lives are recognised as harbouring exceptional, highly endemic fish faunas adapted to the rapids — and, in IUCN's own regional review, as among the African freshwater systems with the highest concentrations of threatened fishes. The ecoregion is also flagged as poorly explored: relatively little is known about its biota, and the DRC's own biodiversity action plan singles out the rapids and waterfalls as habitats most in need of survey work. For Oreochromis lepidurus that combination is the heart of the problem — a narrowly distributed, little-studied species in a stretch of river under mounting industrial pressure, where the data needed to track its decline largely do not yet exist.