Taxonomy & naming
The species was described in 1992 by Melanie L. J. Stiassny, Ulrich K. Schliewen and Wallace J. Dominey as Tilapia imbriferna, in their landmark paper 'A new species flock of cichlid fishes from Lake Bermin, Cameroon' (Ichthyological Exploration of Freshwaters 3(4):311–346), which at a stroke added eight new Tilapia to the lake. The holotype (AMNH 98267) and an extensive paratype series, split between the American Museum of Natural History, the Royal Museum for Central Africa in Tervuren, and the Zoologische Staatssammlung München, all came from Lake Bermin itself, near 5°09′30″N, 9°38′E in the Nguti subdivision of Cameroon's South-West Province. For decades the West and Central African substrate-spawning tilapias were lumped into a sprawling genus Tilapia. The molecular phylogeny of Dunz & Schliewen (2013) dismantled that catch-all, resurrecting Coptodon Gervais, 1853 for the lineage that includes the redbelly tilapias and the entire Bermin radiation, so the fish now stands as Coptodon imbriferna within the tribe Coptodonini. The nine Bermin endemics — among them Coptodon bythobates, Coptodon snyderae, Coptodon gutturosa, Coptodon spongotroktis, Coptodon bemini and Coptodon thysi — form a monophyletic flock that descended from a single ancestral colonist, and they are a textbook (if contested) example of cichlid speciation within a tiny, closed water body.
Morphology
Coptodon imbriferna is a modest-sized, deep-bodied cichlid reaching about 5 in in standard length, placing it among the larger members of the Bermin flock. The fin formula is typical of the genus: roughly fifteen dorsal spines followed by ten to twelve soft rays, and three anal spines with seven or eight soft rays. Its diagnostic features lie in the feeding apparatus and gills rather than in flashy colour. The original describers noted a slender, gracile lower pharyngeal jaw bearing a reduced tooth plate, unusually long gill filaments on the first arch (about a fifth of the head length), and ten to twelve gill rakers on that arch with the front rakers conspicuously shrunken — a combination consistent with a fish that strains fine food from the water rather than crushing hard prey. As in much of the flock, the live colour is a fairly plain olive-to-tan body broken by faint vertical barring, brightening in breeding adults. Across the Bermin Coptodon the sexes are not strongly dimorphic in fixed structures; ripe males and females are told apart mainly by the swollen, paler belly of a gravid female and by behaviour and genital papilla shape around spawning.
Habitat
The entire world range of this fish is one lake. Lake Bermin is a small crater lake in the volcanic highlands of southwestern Cameroon — a near-circular caldera only about 600 metres across and roughly fifteen metres deep at its lowest point, with no inflowing streams and a single small outflow. Because it is so shallow, Bermin does not build the deep, lethal pockets of dissolved gas that make some Cameroonian crater lakes (notoriously Lake Nyos) dangerous, though it does stratify. Coptodon imbriferna lives along the lake margin and is most often associated with the shallows, where like its relatives it forms stable pairs and spawns over sunken wood and stones. What sets it apart from most of the flock is that it migrates seasonally through the water column: recent work on the lake's cichlids found that imbriferna shifts into deeper, darker water during the dry season and returns to the bright surface zone in the wet season, and that its eyes track that movement — dry-season, deeper-dwelling fish down-regulate a short-wavelength (blue-sensitive) opsin to match the dimmer, redder light at depth. Recorded lake conditions are warm and only mildly mineralised: surface temperatures around 75 °F, a near-neutral pH of about 7.5, and low alkalinity, with depth ranging from the shoreline shallows to about the fifteen-metre maximum.
Feeding
Coptodon imbriferna is a herbivore and microphage, sitting low on the food web at an estimated trophic level near 2.6. FishBase characterises it as preferring a herbivorous diet, and notes — tellingly, given its long gill filaments and reduced anterior rakers — that it appears to take phytoplankton directly from the water column rather than scraping it from the substrate. In the broader Bermin community most of the species share a generalised grazing diet of algae, aufwuchs, phytoplankton, insects and detritus; the flock's one true dietary specialist is Coptodon spongotroktis, which has evolved to exploit the lake's freshwater sponges, glassy spicules and all. Within that guild imbriferna reads as a water-column microalgae and phytoplankton feeder rather than a hard-substrate scraper, a role that dovetails with its habit of ranging up and down through the water as the seasons and light change.
Mating
Like the rest of the Bermin Coptodon, imbriferna is a pairing, territorial substrate spawner rather than a mouthbrooder or a harem-former. Field observation describes the species forming stable pairs near the lake shore, with the bonded pair establishing and defending a spawning site on sunken timber or on stones. Outside of reproduction these fish are gregarious and only moderately quarrelsome, but pair formation and spawning sharpen aggression markedly — a pattern consistent across the flock, where a settled pair will hold and defend its patch vigorously against conspecifics. Courtship and site preparation precede egg-laying in the usual tilapiine manner, the pair cleaning the chosen surface before the female deposits her eggs.
Breeding
Coptodon imbriferna is a biparental substrate (open) brooder. In the wild the pair spawns on a cleaned hard surface — sunken wood or a stone — and both parents then guard the brood, the classic shared-care strategy that has made the substrate-spawning tilapias such reliable parents. No precise wild clutch count has been published for this species; across the closely related Bermin Coptodon and other small Coptodon, females lay on the order of a few hundred adhesive eggs per spawning, and the fish mature and breed at a small size. After hatching, the free-swimming fry are shepherded and defended by both parents until they can fend for themselves. The combination of a guarded, demersal egg clutch and attentive biparental defence is the reproductive signature of the whole genus and underlies these fishes' reputation as easy, dependable breeders wherever they have made it into captivity.
In the aquarium
Although it is a Critically Endangered single-lake endemic, Coptodon imbriferna and its Bermin relatives have reached the hobby and are maintained by enthusiasts, several under the CARES Preservation Program that pairs aquarists with at-risk species. They are not difficult fish. Wild parameters are unremarkable — water around 75 °F (the species tolerates the warmer end of a roughly 75–82 °F range in captivity), a near-neutral pH of about 7.5, and soft, low-alkalinity water — and keepers report that the Bermin Coptodon adapt to ordinary, dechlorinated tap water without fuss provided extremes are avoided. A tank of around 35.5 in (three feet) or more suits these medium-sized cichlids; the standard advice is to start with a group of six to eight juveniles and to break up sight lines with driftwood, rockwork, caves and inverted flowerpots so subordinate fish can escape. The crucial caveat is spawning: these fish are peaceable toward tankmates and only mildly scrappy day to day, but a breeding pair becomes fiercely territorial, and it is usually best to move the pair (or the other fish) once eggs appear, or at least keep a divider on hand. They are confirmed plant-eaters — Anubias, Java fern and Java moss are all reported eaten — so live plants serve as food, not décor. Feeding is easy: a quality vegetable-rich (mbuna-type) cichlid pellet plus blanched greens, with only occasional meaty foods, matches their largely herbivorous wild diet; high-protein carnivore foods should be avoided long-term. Robust biological filtration and generous weekly water changes round out their care. Anyone keeping them should treat them as an ark population — keep accurate lineage records and pass surplus fry on to other serious keepers rather than letting a conservation strain dwindle.
Conservation
Coptodon imbriferna is assessed on the IUCN Red List as Critically Endangered (criteria B1ab(iii)+2ab(iii)), assessed by T. Moelants on 16 February 2009 and published in 2010, with population trend unknown. The listing turns on the simplest of facts: the species exists in one tiny crater lake and nowhere else, so its entire extent of occurrence and area of occupancy are minute, and any decline in habitat quality threatens the whole population at once. The named pressures are agricultural. Deforestation of the crater rim, the spread of oil-palm plantations, and slash-and-burn farming around the lake drive sedimentation and pollution into Bermin's small, closed basin. The clearing of surrounding forest also exposes the lake to more wind, raising the risk that its stratified layers could overturn and bring deep, oxygen-poor water to the surface, suffocating the fish — and there is a residual, low-probability threat of a sudden CO₂ release of the kind that devastated Lake Nyos, though Bermin's shallowness makes a catastrophic 'burp' far less likely. Because all nine Bermin endemics share the one vulnerable home, conservation of this lake is effectively conservation of an entire cichlid radiation, which is why captive CARES populations are regarded as a meaningful insurance against loss.