Taxonomy & naming
Coptodon ejagham was described in 2010 by Andreas R. Dunz and Ulrich K. Schliewen, in a Spixiana monograph (33: 251–280) that formally erected the Lake Ejagham Tilapia flock — three new species at once, alongside a redescription of the long-known Tilapia deckerti. At description the fish was placed in Tilapia in the wide old sense, within the subgenus Coptodon; the same authors' 2013 molecular phylogeny of the haplotilapiine cichlids (Molecular Phylogenetics and Evolution 68: 64–80) then elevated Coptodon to full genus rank, and the combination Coptodon ejagham has stood since. The genus gathers the West and Central African biparental substrate-spawning tilapiines — fish such as the redbelly tilapia Coptodon zillii and Coptodon rendalli — and is sharply distinguished from the mouthbrooding tilapiines (Oreochromis, Sarotherodon) by reproductive mode. Within Coptodon, Coptodon ejagham keys out on a suite of fine morphometric characters and on its pharyngeal dentition: tricuspid (rarely quadricuspid) teeth in the posterior rows of the lower pharyngeal jaw, a feature shared with only a couple of other lineages. It is one of three endemic Coptodon in Lake Ejagham — the predatory Coptodon ejagham, the benthivorous Coptodon deckerti, and the zooplanktivorous Coptodon fusiforme — which together form the lake's substrate-spawning species flock; a second, independent radiation of mouthbrooding Sarotherodon (Sarotherodon knauerae, Sarotherodon lamprechti) shares the same water, making Ejagham the only crater lake known to host two separately speciating cichlid lineages at once. The type locality is simply Lake Ejagham, Cameroon.
Morphology
Coptodon ejagham reaches about 8 in in standard length, the largest of the lake's three Coptodon and a fish built for an active, predatory life. The body is comparatively slender and elongate for a tilapiine — its body depth runs roughly 34–41% of standard length, distinctly lower than the deep-bodied congeners (Coptodon rendalli, Coptodon dageti and kin) that sit around 41–51% — and the head is long, giving the fish a streamlined, fusiform outline. The dorsal fin carries 15–16 spines and 10–12 soft rays, the anal fin 3 spines and 8–10 soft rays, and there are 9–10 gill rakers on the first ceratobranchial. Dunz and Schliewen separated it from its lakemates on a tight cluster of measurements: it differs from the benthivore Coptodon deckerti in its shorter eye, and from the zooplanktivore Coptodon fusiforme in its noticeably longer snout, the kind of small trophic-feeding distinctions one expects of incipient species partitioning a single small habitat. Flank scales carry dark margins around a lighter centre, especially below the lateral line — a pattern that distinguishes it from the dark-blotched congener Coptodon nigrans. Because the three Ejagham Coptodon are recently and incompletely diverged, the species also separate by colour and size in life; field work in the lake found mate choice tracking colour, body size and head depth, all of which differ subtly between the predator and its benthic and pelagic relatives. The sexes are not strongly dimorphic in the marked way of many cichlids, but as in Coptodon generally, breeding adults of both sexes intensify in colour and pattern when they pair and hold a nest.
Habitat
The entire world range of Coptodon ejagham is Lake Ejagham, a small lake near the village of Eyumojock in the Southwest Region of Cameroon, lying at roughly 656 ft elevation in lowland evergreen rainforest. The lake is tiny and young: about 0 mi² in surface area, only around a kilometre across, with a single small outlet and a maximum depth of about 56–59 ft. Sediment cores date its origin to roughly 9,000 years ago, and — unusually for the region — it is probably not a volcanic crater; geological work suggests it may instead be a suspected bolide-impact crater, and in any case it has held stable water chemistry and depth across its whole existence, an environmental constancy that makes it a near-ideal natural laboratory for in-situ speciation. The water is warm and circumneutral: regional air temperatures run from about 68–91 °F with monthly means of 77–82 °F, and measured conductivity is moderately elevated at 86–120 µS/cm, plausibly fed by the saline springs that thread the surrounding Mamfe sedimentary basin. The basin has a broad, flat floor of fine organic mud offshore and a narrow belt of sandy shallows that drop steeply from the shoreline. Coptodon ejagham concentrates in those inshore shallows — non-breeding fish range solitarily through the lake hunting, while breeding is confined to the shallow margin above about 7 ft depth, among the submerged branches and logs of the flooded forest edge.
Feeding
Among the Ejagham Coptodon, Coptodon ejagham is the predator. Where Coptodon deckerti works the bottom as a benthivore and Coptodon fusiforme strains zooplankton from open water, Coptodon ejagham hunts other fish. Field observations recorded non-breeding individuals moving alone and almost continuously, swimming without haste but rarely resting, permanently scanning the surroundings for prey; the same observations identify it as a predator of small fish, mostly juvenile cichlids — which in this enclosed lake means largely the fry and young of its own relatives. This piscivorous habit is the species' principal trophic novelty and the axis along which it has diverged from its benthic- and plankton-feeding lakemates. The genus Coptodon as a whole leans herbivorous-omnivorous (Coptodon rendalli and Coptodon zillii are classic macrophyte grazers), so a small-fish predator is an unusual specialization for the lineage, and one of the clearest signs that the Ejagham flock has remodelled its feeding ecology rapidly within the lake. FishBase's modelled trophic level of about 2.5 is a conservative size-based estimate and likely understates the role of fish prey in a true piscivore.
Mating
Lake Ejagham is celebrated precisely because mate choice here appears to be driving speciation in the absence of any geographic barrier. Detailed field study of the flock found strong assortative mating: pairs form along independent axes of colour, body size, head depth and the benthic-versus-pelagic source of their diet, so that fish resembling one another and feeding alike tend to breed together. That non-random pairing is the engine that keeps the predatory, benthic and planktivorous forms partially reproductively isolated even as they share one small body of water — although the same work concluded that the divergence remains incomplete, with assortment strong but progress toward full speciation limited, which is why the forms are best described as incipient species. In practical terms, when a Coptodon ejagham comes into breeding condition it abandons its solitary hunting and forms a pair, the two fish together claiming and defending a patch of the shallow inshore zone. Pre-spawning behaviour follows the standard substrate-spawning tilapiine template of paired site-holding and joint territory defence rather than the lek-and-mouthbrood pattern of the lake's Sarotherodon.
Breeding
Coptodon ejagham is a biparental substrate spawner, the ancestral and defining reproductive mode of the genus. Breeding is restricted to the shallow inshore region above roughly 7 ft depth, where a pair excavates a large nest-pit beneath a big submerged branch or log — using the woody cover of the flooded forest margin as a roof over the spawning site. As in other Coptodon, eggs are laid on a cleaned hard surface within the pit and both parents share guarding and brood care: the adhesive eggs are fanned and defended in place, and after hatching the wrigglers and free-swimming fry are tended and shepherded by both fish, a contrast with the mouthbrooding Sarotherodon that share the lake. Specific clutch counts for Coptodon ejagham have not been published, but substrate-spawning Coptodon are moderately fecund cichlids that typically lay on the order of several hundred to a thousand or more eggs per spawning, well above the small clutches of mouthbrooders. FishBase rates the species' resilience as high, with a minimum population-doubling time under fifteen months, consistent with a fish that can produce sizable broods of guarded young in warm water — the reproductive output is not the problem; the survival of those young in a tiny lake now stocked with an introduced predator is.
In the aquarium
Coptodon ejagham is not an aquarium fish in any meaningful sense. It is a Critically Endangered single-lake endemic with no presence in the ornamental trade; it is known to science from research collections and field study, not from the hobby, and it should not be sought, bought or wild-collected. The notes here are therefore husbandry by analogy with its better-known substrate-spawning Coptodon relatives, offered for context rather than as a keeping guide. Were such a fish ever held in a legitimate conservation or research setting, the requirements would be those of a medium-large, active, predatory tilapiine: a long tank measured in metres rather than centimetres to accommodate a roughly 8 in fish that swims more or less constantly, warm water around 77–82 °F, near-neutral pH and moderate, slightly mineralized hardness in line with its lake's circumneutral, 86–120 µS/cm chemistry. A sand substrate and large pieces of bogwood would let a pair express its natural pit-digging under cover, and the fish would need a diet built around whole foods appropriate to a piscivore. The intrinsic problems are obvious — Coptodon are territorial diggers that uproot plants and rework the substrate, and a piscivore will eat anything small enough to swallow, including its own young between broods — but the decisive point is conservation, not difficulty: a fish reduced to a 2 mi² range belongs in protected habitat and managed programmes, not in private tanks.
Conservation
The IUCN Red List assesses Coptodon ejagham as Critically Endangered (criteria B1ab(iii)+2ab(iii)), assessed on 9 March 2023 by C.H. Martin, with population trend unknown. The listing turns entirely on the species' minute, single-site range: both its extent of occurrence and area of occupancy are estimated at just 2 mi², the whole of Lake Ejagham, so any decline in the quality of that one habitat threatens the entire species. The threats the assessment names are concrete. Around 2000–2001 a local official introduced large numbers of catfish to the lake, establishing a breeding population of a predatory Parauchenoglanis that was still present years later and that competes with and preys on the native cichlids — an acute danger to a fish whose own young are part of the lake's small-fish prey base. Compounding this are deforestation in the watershed, the increased erosion and siltation that follows it, and unsustainable extraction of water from a basin that holds so little to begin with. Because Ejagham is shallow, young and hydrologically simple, it has limited buffering against these pressures, and the same isolation that allowed Coptodon ejagham to evolve in place now leaves it with nowhere to retreat. Protecting the species means protecting the single lake — controlling the introduced catfish, halting watershed deforestation and water withdrawal, and safeguarding a globally unique evolutionary system that exists in no other water on the planet.