Taxonomy & naming
The species was described by the French ichthyologist Jacques Daget in 1962, as Tilapia rheophila, in his memoir on the fishes of the Niger and adjacent Guinean drainages (Mémoires de l'Institut français d'Afrique Noire No. 65). The type series — five syntypes catalogued as MNHN 1959-0106, with further material under MNHN 1960-0488 and 1960-0489 — came from what Daget loosely termed 'Lower Guinea,' and the species is in practice tied to the Konkouré River system. The epithet is straightforwardly descriptive: rheophilus, 'current-loving,' from the Greek rheos (current, stream) and philos (loving), for a fish of running water. Eschmeyer's Catalog of Fishes notes that Daget did not explain the name but treats it as an adjective, which is why the current spelling is the masculine rheophilus to agree with the masculine genus Coptodon — even though FishBase still files the species under the older feminine spelling rheophila.
For half a century the fish sat in the vast, paraphyletic catch-all genus Tilapia. That changed with the molecular work of André Dunz and Ulrich Schliewen, whose 2013 phylogeny of the 'haplotilapiine' cichlids formerly lumped as Tilapia (Molecular Phylogenetics and Evolution 68) broke the old assemblage into a series of natural genera. They resurrected Coptodon Gervais, 1853 — a name long available but little used — for the large clade of substrate-spawning West and Central African tilapias that includes the familiar Coptodon zillii and Coptodon rendalli. Tilapia rheophila was duly recombined as Coptodon rheophilus, the placement the Catalog of Fishes and FishBase now follow. The species is closely allied to, and easily confused with, the later-described Coptodon konkourensis from the same river, and Dunz and Schliewen's 2012 description of that fish (Zootaxa 3314) is in part a re-examination of Daget's rheophila material.
Morphology
Coptodon rheophilus is a small tilapia, reaching only about 4 in in total length (FishBase) — modest by the standards of a genus whose better-known members run to 10–12 in. It has the general Coptodon build: a moderately deep, laterally compressed body, a single continuous dorsal fin, and the genus's diagnostic pharyngeal apparatus. The published meristics give 16 dorsal spines and 10–12 soft dorsal rays, three anal spines and 7–8 anal soft rays, with 12–14 scales on the caudal peduncle and 8–9 lower gill-rakers. The lower pharyngeal bone is about as long as broad, its anterior (toothed-area) lamella shorter than the toothed surface, and the median pharyngeal teeth are not broadened — the standard Coptodon condition, and one of the features that separate the genus from related tilapiine lineages.
As in other Coptodon, the body carries the genus's vertical barring rather than the horizontal-stripe pattern of some relatives. Live coloration in life is not well documented for this little-photographed species — FishBase carries no photograph — so detailed notes on breeding dress and sexual differences are lacking. The most reliable way to separate rheophilus from its Konkouré congener Coptodon konkourensis is by body proportions and meristics: konkourensis is even more slender (body depth roughly 30–31.5 % of standard length, against a deeper body in rheophilus), has a slightly larger eye, a longer pectoral fin and a shorter dorsal-fin base. These are fine, near-cryptic distinctions, and the two species are best told apart by direct measurement rather than at a glance.
Habitat
True to its name, this is a fish of fast water. FishBase characterises it as a rheophilic, freshwater, benthopelagic species, and treats it as endemic to the middle Konkouré River in Guinea, between roughly 10° and 11° N. The Konkouré is a relatively short but steep West African river, draining the Fouta Djallon highlands and dropping through a series of rapids and gorges on its way to the Atlantic — habitat that strongly favours torrent-adapted, bottom-oriented fishes over the open-water, lake-loving tilapias of the great African lakes. Within Africa's freshwater ecoregion scheme the Konkouré falls in the Fouta Djallon ecoregion (FEOW), a highland province known for a cluster of small-range rheophilic endemics.
The species' tight association with one river system, and with the rapids habitat in particular, makes it a narrow-range endemic of exactly the kind that is vulnerable to localised change — most obviously to hydropower development on the Konkouré, which has been extensively dammed. No detailed field study of its preferred microhabitat (substrate, depth, flow velocity) has been published, so the picture here is built from its morphology, its named affinity for current, and the general character of the middle Konkouré rather than from dedicated ecological survey.
Feeding
No direct dietary study of Coptodon rheophilus has been published, and FishBase records no quantified diet for the species; its trophic level (about 2.7) is an estimate based on body size and the diets of its closest relatives rather than on gut-content data. The genus Coptodon as a whole is dominated by herbivores and detritivores — Coptodon zillii and Coptodon rendalli are classic macrophyte- and algae-grazers, and the better-studied West African congeners are described as 'mainly herbivorous, but also taking small amounts of insects.' A rheophilic Coptodon of fast, rocky water would most plausibly graze the algal and biofilm growth ('aufwuchs') that coats stones in rapids, supplemented by the small invertebrates that live among it. That is a reasonable inference from the genus and the habitat, but it should be read as such: the specific feeding ecology of this fish has not been documented.
Mating
Like the other Coptodon, rheophilus is understood to be a pair-bonding substrate spawner rather than a mouthbrooder — the reproductive divide that separates Coptodon from the mouthbrooding food-tilapias of the genera Oreochromis and Sarotherodon. In the Coptodon pattern, a male and female form a monogamous pair, jointly establish and defend a territory on the bottom, and remain together through the breeding cycle. The specifics of courtship, pair formation and territorial behaviour have not been described for this species in the wild; what can be said is drawn from the consistent biology of its better-known congeners, in which a bonded pair clears and defends a nest site and both partners share in guarding the brood. There is no reason to think rheophilus departs from that genus norm, but its mating behaviour has not been directly observed and recorded.
Breeding
FishBase summarises the reproduction of the West African Coptodon species, this one included, as 'probably pair-bonding, open substratum spawner, with both parents guarding the brood' — the qualifier 'probably' signalling that the behaviour is inferred from close relatives rather than documented for rheophilus itself. In substrate-spawning Coptodon the adhesive eggs are laid on a cleaned hard surface or in an excavated depression and are tended by both parents, which fan the clutch and guard the wrigglers and free-swimming fry; in some congeners the pair digs a large, deep pit as the nest. Clutch size, egg number, spawning season and fry development have not been published for this species. In short, rheophilus is confidently placed among the biparental substrate-spawners by genus membership, but its breeding has not been studied in detail in the wild or in captivity, and no aquarium spawning reports exist for it.
In the aquarium
Coptodon rheophilus is essentially unknown in the aquarium hobby. It is not a traded species, it has no aquarium-strain history, and — being a small, narrow-range Guinean rheophile rather than a showy or food-relevant tilapia — it has never entered the ornamental trade in any meaningful way. There is accordingly no body of keeper experience to draw on, and nothing here should be read as a maintenance recommendation for a fish that is, in practice, not available.
What can be said is general and inferential. Were specimens ever to reach hobbyists, the obvious requirement would be flow: this is a current-adapted fish from rocky rapids, so a tank emulating a fast-water biotope — strong circulation, well-oxygenated water, a substrate of sand with rounded stones and cobbles, and warm tropical temperatures in the high-20s Celsius — would be the sensible starting point, modelled on how aquarists keep other rheophilic West African cichlids. Even then, as a small substrate-spawning tilapia, it would likely show the territorial, pit-digging tendencies of its genus around breeding. But these are extrapolations from habitat and relatives, not tested husbandry; the honest summary is that this species is a wild, little-studied endemic with no real aquarium presence.
Conservation
Coptodon rheophilus has not been assessed by the IUCN Red List — its status is recorded as Not Evaluated — so there is no formal extinction-risk category for it. That gap is itself worth flagging, because the species has the profile that usually warrants concern: a small-bodied fish apparently restricted to a single river system, the Konkouré, in the Guinean highlands. The Konkouré has been a focus of hydropower development, and dams, flow alteration and habitat fragmentation are the kinds of pressures that bear hardest on rheophilic, rapids-dependent endemics with nowhere else to go. Several of its near-neighbours in the same drainage and the same fast-water guild have been recognised as range-restricted and potentially threatened. Without a dedicated assessment, however, any statement about its true conservation status would be speculation; what is clear is that it is a narrow-range Guinean endemic for which up-to-date population and threat data are simply lacking. It carries no CITES listing and is of no fishery interest.