Taxonomy & naming
Coptodon flavus was described in 1992 by Melanie L. J. Stiassny, Ulrich K. Schliewen and Wickham (Wallace) J. Dominey as Tilapia flava, one of eight new tilapiine species named in their paper 'A new species flock of cichlid fishes from Lake Bermin, Cameroon' (Ichthyological Exploration of Freshwaters 3: 311–346). Together with the earlier-described Tilapia bemini (Thys van den Audenaerde, 1972) and the other seven species from the same paper — Tilapia bakossiorum, Tilapia bythobates, Tilapia gutturosa, Tilapia imbriferna, Tilapia snyderae, Tilapia spongotroktis and Tilapia thysi — it makes up the nine-species Lake Bermin cichlid flock, one of the textbook examples of cichlid diversification within a single small lake. All nine species were long carried under the broad, catch-all genus Tilapia. Dunz and Schliewen's 2013 molecular revision of the haplotilapiine cichlids formerly placed in Tilapia resurrected the genus Coptodon Gervais, 1853 for the West and Central African substrate-spawning tilapiines, and the species has been recognized as Coptodon flavus since. The Bermin flock is thought to descend from a single riverine Coptodon ancestor related to the West African Coptodon guineensis group, though subsequent genomic work has shown these Cameroonian crater-lake radiations to have more complicated, gene-flow-affected histories than the original, simpler sympatric-speciation account implied.
Morphology
Coptodon flavus is a small, deep-bodied, laterally compressed cichlid typical of the compact body plan shared across the Lake Bermin flock, whose nine species range from roughly 2–7 in and are distinguished from one another chiefly by subtle differences in mouth and lip structure, dentition and breeding colour rather than by any single dramatic feature. Consistent with its epithet, flavus is characterised by a yellow ground colour, intensifying in breeding condition as in several of its lake-mates, though a precise, source-verified account of its fin counts and specific colour pattern relative to its eight congeners is not confirmed in the material available for this article — data sparse on the fine diagnostic detail that separates it from Coptodon gutturosus, Coptodon imbrifernus and the rest of the flock.
Habitat
The entire known range of Coptodon flavus is Lake Bermin, a small volcanic crater lake in the Bakossi Mountains of south-western Cameroon, on the order of 60 hectares in surface area and around 600 metres across, with a maximum depth of roughly 48 ft. The lake has no significant inflowing river and drains through a single small outlet stream, which has sealed the flock inside one basin for long enough to diversify into nine morphologically and ecologically distinct species. Recorded conditions in the lake are warm and only lightly mineralised — surface water around 75 °F, pH near neutral to mildly alkaline, and low hardness — and Coptodon flavus, like its lake-mates, is expected to occupy the shallow littoral zone around submerged wood and algae-and-sponge-covered substrate rather than open water.
Feeding
The Lake Bermin Coptodon flock is predominantly herbivorous and detritivorous, grazing algae, plant material and detritus from submerged surfaces, and several species — most famously Coptodon spongotroktis — also feed on the freshwater sponges that grow in the lake, an unusual food source for a fish given their glassy silica spicules. Coptodon flavus is presumed to share this broadly herbivore/detritivore feeding mode typical of the flock, though a species-specific dietary study is not confirmed in the sources available here.
Mating
No species-specific courtship account for Coptodon flavus is confirmed in the sources available for this article. Its lake-mate Coptodon bakossiorum is documented as a pair-bonding, substrate-spawning cichlid that is largely tolerant outside the breeding season but becomes assertively territorial around a chosen spawning site, a pattern typical of small Coptodon generally; C. flavus is presumed to follow a broadly similar reproductive strategy, but this is inference from the genus and flock rather than direct observation of the species.
Breeding
Coptodon flavus is presumed, on genus- and flock-wide grounds, to be a biparental, open substrate spawner like its documented lake-mate Coptodon bakossiorum, with the pair sharing a nest site, the female tending the eggs and the male defending the territory. No clutch size, incubation period, or captive-breeding record specific to Coptodon flavus is confirmed here — data sparse.
In the aquarium
Lake Bermin Coptodon are established, if specialist, CARES Preservation Program fish, kept by African-cichlid enthusiasts specifically to maintain a documented captive lineage as insurance against the fragility of the wild population; several of the flock's better-documented members (Coptodon bakossiorum, C. bemini, C. bythobates) are known to be hardy, adaptable aquarium fish given warm, only moderately hard water, a herbivore-leaning diet and enough décor to give subordinate fish refuge from territorial pairs. Coptodon flavus is expected to require broadly similar care, but species-specific husbandry notes for this particular member of the flock are not confirmed in the sources available here, and any keeper obtaining this species should treat detailed parameters as provisional pending direct confirmation.
Conservation
As with the rest of the Lake Bermin flock, Coptodon flavus's entire world range is a single crater lake of well under 100 km2, placing it well within the geographic thresholds the IUCN uses to assign Critically Endangered status; its documented lake-mates Coptodon bakossiorum and Coptodon bythobates carry exactly that IUCN assessment (Moelants, assessed 2009), and flavus is very likely to have been assessed under the same review given its identical single-lake range, though an independently confirmed species-specific IUCN record for flavus itself is not available in the sources used for this article. The pressures affecting the lake generally include agricultural and forestry runoff and wood harvesting in its small catchment, together with the latent geological hazard inherent to any volcanic crater lake. The CARES Preservation Program's Critically Rare listing for this species reflects that same acute vulnerability, and a maintained captive population is a meaningful hedge given that no other wild population exists anywhere else on Earth.