Taxonomy & naming
The Swedish zoologist Einar Lönnberg described this fish as Tilapia kottae in 1904, in a short paper titled 'On some fishes from the lakes of the Cameroon Mountain' published in the Annals and Magazine of Natural History. His material came from Lake Barombi-ba-kotta — the crater lake now usually written Barombi Koto — on the flanks of the Cameroon volcanic line, and the syntype series is split between the Natural History Museum in London (BMNH 1904.2.15.1-2) and the Swedish museum collections at Uppsala and Stockholm (NRM and ZMUU). For most of the twentieth century it sat, like dozens of other small African substrate-spawners, in the catch-all genus Tilapia. That changed with the molecular phylogeny of Dunz and Schliewen (2013), who dismantled the old grab-bag 'Tilapia' and resurrected several older genus names to match the true branches of the tilapiine tree. Their work placed kottae in the genus Coptodon Gervais, 1853 — the West and Central African biparental substrate-brooders of the tribe Coptodonini — so the fish is now properly Coptodon kottae (Lönnberg, 1904), the parentheses recording that it was first named in a different genus. The species had earlier featured in a body of work by Dunz and Schliewen (2010, 2012) on the Cameroonian crater-lake tilapias, including the Lake Ejagham Coptodon species flock, which examined the morphological variability of kottae across Barombi Koto and Mboandong and its affinities with other tilapias of the Cameroon volcanic line.
Morphology
Coptodon kottae is a modestly sized, deep-bodied cichlid of typical tilapiine build, reaching about 6 in in total length. The fin counts given in its diagnosis are a useful fingerprint: the dorsal fin carries 14-16 spines and 10-13 soft rays, the anal fin 3 spines and 8-9 soft rays, there are 28-30 scales along the lateral line, and 8-10 gill rakers on the lower limb of the first gill arch. Colour is strongly mood- and season-dependent, which is the trait that gives the fish its reputation. Non-breeding adults and freshly caught fish are a plain, unremarkable grey, easily mistaken for any number of generic tilapias; but in breeding condition the body lights up to a clean, saturated lemon- to golden-yellow, and it is this dress that has earned it a small following among crater-lake cichlid enthusiasts. Sexual dimorphism is modest and behavioural as much as structural: as in most Coptodon, both sexes can take on breeding colour, ripe females become noticeably rounder and fuller-bodied with the egg mass, and males tend to be the larger, more robust fish, with the pair-bonded male typically holding and defending the territory. The species' separation from its near-relatives elsewhere on the Cameroon volcanic line rests on subtle, overlapping morphometric and meristic differences rather than any single striking feature, which is part of why earlier authors lumped so many of these crater-lake forms together.
Habitat
The whole range of Coptodon kottae is two crater lakes in the Southwest Region of Cameroon: Lake Barombi ba Kotto (Barombi Koto) and the much smaller Lake Mboandong, both within the Meme River catchment near Kumba. Barombi Koto is a shallow volcanic crater lake roughly 1 mi across and, in most places, less than 20 ft deep, ringed by a forested-then-cultivated crater wall and dotted with a densely settled central island. The water is warm — field measurements sit around 75–79 °F — and only weakly stratified, carrying a dense phytoplankton bloom dominated by blue-green algae that tints and clouds the water. In-situ readings from the lake and its feeder streams are soft and close to neutral: conductivity under about 100 µS/cm, pH near 6.8-7.0, with a sandy or silty bottom in the open shallows and accumulations of leaf litter, branches and roots along the shaded, vegetation-overhung margins. The lake has only two small intermittent inflow streams (the Tung Nsuia and Tung Nsuria, each barely a metre or so wide and shallow) and a single intermittent outflow toward the Meme River, both of which dry out or shrink dramatically in the dry season. Within this small system kottae is the sole endemic cichlid, sharing the water with the introduced or wide-ranging Chromidotilapia guentheri, Hemichromis fasciatus, Pelmatolapia mariae and Sarotherodon galilaeus, plus a Clarias catfish, the barb Enteromius callipterus and a fauna of killifishes in the inflow streams.
Feeding
Coptodon kottae is a low-trophic-level grazer and generalist, in keeping with the herbivorous-to-omnivorous habits of the genus. Its diet consists primarily of plant material and small particles — detritus and the algal-and-microorganism film known as aufwuchs — which it crops and gleans from surfaces and sediment rather than hunting prey. FishBase places its estimated trophic level near 2.6, at the herbivore/detritivore end of the spectrum. In the crater-lake community at Barombi Koto, the cichlids partition the food base: of the species present, several (including kottae) are essentially phytoplankton- and plant-feeders, while others specialise on chironomid larvae or on small fish and invertebrates. The dense blue-green algal bloom that characterises the lake's water is, in effect, the base of the food web this fish exploits. The three phytoplankton-feeding cichlids of the lake — kottae among the most important — are also the chief species taken by the local fishery for food.
Mating
Like other Coptodon, kottae is a pair-bonding substrate spawner rather than a harem-forming mouthbrooder, and its reproductive behaviour reorganises a pair of fish around a defended nest site. When ready to breed, a male and female form a bond, both assume the bright yellow breeding livery, and together they stake out and defend a territory centred on a sheltered spawning site — typically a crevice, an overhang, or the hollow of sunken wood. The fish prefer obscured, partly enclosed places to spawn rather than an exposed flat surface, which fits a small fish in a predator-rich lake where eggs laid in the open are quickly lost. Pair formation and territorial defence are cooperative: both partners drive off intruders, and the bond persists through spawning and the long period of brood care that follows. This biparental, monogamous system — bright synchronised colour change, a jointly held territory, and shared defence — is the behavioural signature that separates the Coptodon substrate-spawners from the mouthbrooding tilapiines, and it is what makes kottae a manageable and rewarding fish to breed in captivity despite its rarity in the trade.
Breeding
Coptodon kottae is a biparental substrate brooder. The pair spawns on a cleaned, hidden surface in an obscured location — a crevice, a sheltered rock face, or inside a hollow in sunken wood — depositing adhesive eggs that both parents then guard and tend. As is typical of the genus, both adults take an active role: the eggs are fanned and defended, and once the young hatch and become free-swimming the parents continue to herd and protect the school of fry as a bonded pair, a level of shared care that contrasts sharply with the female-only mouthbrooding of Oreochromis and Sarotherodon. The species is reported to be very easy to breed in the aquarium, and its substrate-spawning, fry-guarding habits make rearing the young straightforward once a compatible pair has formed. Precise wild clutch counts for kottae do not appear to have been published; congeneric Coptodon substrate-spawners of similar size typically lay on the order of a few hundred to roughly a thousand eggs per spawning, and that genus-typical figure is the best available guide. The combination of high fecundity, a short generation time and diligent biparental care gives the species a high biological resilience, which is one of the few bright spots for a fish whose wild range is so tightly confined.
In the aquarium
Coptodon kottae is a genuine rarity in the hobby — it has gone years between imports — but on the occasions it has reached aquarists it has proven undemanding and easy to spawn, and it has a modest, devoted following among keepers of Cameroon crater-lake cichlids. A pair can be housed in an aquarium of around 30 US gallons (roughly 30 US gal) or more; a longer tank is better, both to let a pair establish a territory and to give other fish room to stay clear of a spawning couple, since like most substrate-spawning cichlids these fish become pointedly territorial and aggressive when they have eggs or fry to defend. Water chemistry should mirror the lake: warm (about 75–82 °F), soft, and near neutral (pH roughly 6.5-7.5), with no need for the hard, alkaline conditions associated with Rift Lake cichlids. Provide a sandy or fine substrate and, crucially, plenty of structure — rockwork with crevices, caves, and pieces of bogwood — so a pair can choose an obscured spawning site of the kind they favour in the wild. Feeding is easy: as a plant-and-detritus grazer the species does well on a vegetable-forward diet, including spirulina or algae-based prepared foods, blanched greens and quality flake or pellet, supplemented with the occasional meaty item. The two things to plan for are the breeding aggression (give tankmates space, and keep companions that can hold their own without being targets) and the fish's everyday plainness — buyers expecting the breeding-dress yellow should know that a settled, non-spawning fish is simply grey. Beyond that, kottae is hardy and long-lived in well-kept water, and keeping it is, in a small way, an act of conservation: with the wild population threatened, captive-maintained lines preserve a fish that exists in only two lakes.
Conservation
The IUCN Red List assesses Coptodon kottae as Endangered (EN), under criteria B1ab(iii)+2ab(iii), in an assessment dated 16 February 2009 by T. Moelants (published as an amended version in 2017). The listing reflects the species' single overriding vulnerability: its entire global range is two small crater lakes, Barombi Koto and Mboandong, so any degradation of those waters threatens the whole species at once. The documented pressures are local and intensifying. Oil-palm plantations and slash-and-burn agriculture on the crater slopes drive sedimentation and nutrient pollution into Barombi Koto, which doubles as the drinking-water source for the lakeside community. Deforestation of the crater rim is a subtler danger: by exposing the lake to more wind it raises the risk of the stratified water column overturning, mixing the oxygen-poor, organic-rich bottom layer into the shallow zone where the fish live and potentially triggering a mass fish kill. There is even a remote possibility of a limnic CO2 release of the catastrophic kind seen at nearby Lake Nyos and Lake Monoun, though Barombi Koto is generally considered too shallow to store dangerous volumes of the gas. The fish is also harvested for food by the local fishery. None of these threats is hypothetical for a single-lake endemic, and the species' value lies as much in its fragility as in its biology: it is exactly the kind of narrow-range crater-lake cichlid for which captive-breeding programmes such as the CARES initiative exist.