Taxonomy & naming
Coptodon spongotroktis was described in 1992 by Melanie L. J. Stiassny, Ulrich K. Schliewen and Wallace J. Dominey as Tilapia spongotroktis, in their landmark paper 'A new species flock of cichlid fishes from Lake Bermin, Cameroon, with a description of eight new species of Tilapia' (Ichthyological Exploration of Freshwaters 3(4): 311–346). The species account begins on page 337, and the holotype — an adult collected in Lake Bermin — is held at the American Museum of Natural History (AMNH 98258), with paratypes distributed among the AMNH, the Zoologische Staatssammlung München (ZSM) and the Royal Museum for Central Africa in Tervuren (MRAC). The type locality is Lake Bermin itself, at roughly 5°09′30″N, 9°38′00″E in the Nguti subdivision of Cameroon's South West Province. For most of its published life the fish carried the catch-all genus name Tilapia, but that genus had long been recognized as a holding bin for unrelated substrate-spawning lineages. Dunz and Schliewen's molecular phylogeny and revised classification of the haplotilapiine cichlids (2013) split the old Tilapia apart, and the Bermin flock — together with the West African 'Tilapia zillii' group — was transferred to the resurrected genus Coptodon Gervais, placed in the tribe Coptodonini. The combination Coptodon spongotroktis has been the valid name since. The 1992 paper is notable beyond this one species: it formally recognized the entire Lake Bermin radiation, a flock of (as currently counted) nine endemic Coptodon that descend from a single colonizing ancestor and now coexist, reproductively isolated, in one of the smallest lakes ever shown to host a cichlid species flock.
Morphology
Coptodon spongotroktis is a modestly sized, deep-bodied cichlid; FishBase lists a maximum of about 5.5 in standard length, and aquarium fish generally stay a little smaller. The fin counts run to 15–16 dorsal spines and 10–11 dorsal soft rays, with three anal spines and eight anal soft rays, the typical Coptodon configuration. What sets the species apart is its feeding apparatus, which the describers diagnosed in detail. The lower pharyngeal jaw is robust and bears a large, triangular (rather than heart-shaped) tooth plate covered in stout, sparsely spaced teeth — a heavy mill rather than a fine grinder. The oral dentition is coarse, with stout bicuspid teeth in the outer row, two to four inner tooth rows in the upper jaw and two to three in the lower, and a relatively short, broad lower jaw (its length usually less than its width). The snout is acute, the lower lip has a smooth ventral margin, and the 12–14 gill rakers are stout and fleshy, linked by a crenulate median membrane between the outer and inner rows — a built-in strainer-and-crusher that fits a diet of sponges and aufwuchs. In life the fish is a fairly plain tilapiine in build, but, as in its relatives, breeding adults intensify in colour. Sexual dimorphism is the modest tilapiine kind: males tend to grow somewhat larger and become more strongly coloured when in condition, while ripe females are deeper-bellied; the sexes are not dramatically different and are best told apart by venting and breeding behaviour rather than by any single fixed external trait.
Habitat
The entire known range of Coptodon spongotroktis is Lake Bermin, a small volcanic crater lake (also spelled Barombi-Koto in older literature, though it is distinct from Lake Barombi Mbo) set into an extinct caldera in southwestern Cameroon. The lake is minute — only about 600 metres across, roughly 0 mi² in surface area — and shallow for a crater lake, reaching only some 15 metres at its deepest. It has no significant inflowing streams and a single small outflow, leaving it effectively a closed evolutionary arena. Reported in-situ conditions are warm and unremarkable by tropical standards: surface temperatures around 75 °F, a pH near 7.5, and soft water with low alkalinity. Its shallowness is, paradoxically, a measure of safety: deep Cameroonian crater lakes such as Nyos and Monoun can accumulate dissolved carbon dioxide in their depths and 'turn over' catastrophically, but a 15-metre lake is far less prone to that kind of limnic eruption. Within the lake spongotroktis shares the water with the eight other endemic Coptodon of the flock, all packed into the same small basin; the species is benthopelagic, foraging over the substrate and submerged surfaces where freshwater sponges and algal growth develop. Ecological surveys of the lake report it as common in the deep zone as well as in the shallows, so it ranges across the lake's full depth profile from the shoreline down to its roughly 15-metre floor.
Feeding
Coptodon spongotroktis is, as its name promises, a freshwater-sponge specialist — a genuinely rare trophic niche among fishes, since sponge tissue is both nutritionally poor and physically defended by glassy silica spicules. FishBase, citing the descriptive literature, records that it feeds mainly on freshwater sponges, supplemented with filamentous algae, phytoplankton and small amounts of insects. Its robust, triangular lower pharyngeal mill and coarse, stout oral teeth are exactly the equipment such a diet demands: a crushing apparatus capable of processing spicule-laden material that would defeat a fine-toothed grazer. In effect the fish has evolved to make a living off what amounts to eating broken glass. This specialization is central to the Lake Bermin story. The flock is striking because, unlike the textbook adaptive radiations of the Rift Lakes, most of the Bermin Coptodon share broadly similar diets of algae, detritus and aufwuchs in a small, fairly uniform lake — making the diversification hard to explain by ecological niche-partitioning alone. Spongotroktis is the conspicuous exception: it alone has cracked a resource its lake-mates largely cannot use, while still taking the same general fare (phytoplankton, algae, insects) when sponges are scarce. It is thus best read as an opportunist with a specialist's toolkit rather than an obligate spongivore.
Mating
Coptodon, like the wider tribe of West and Central African substrate-spawning tilapiines, are biparental and territorial breeders, and spongotroktis follows that template. Outside of reproduction the Bermin Coptodon are relatively peaceable and shoaling, but as fish come into spawning condition they pair off and become markedly aggressive in defence of a chosen site. Pair formation is mutual: a male and female bond and together clear and guard a patch of substrate, displaying to each other and driving off intruders — including their own packed-in lake-mates — through the run-up to spawning. In the confines of Lake Bermin, where nine species crowd a single small basin, that territorial intensity around breeding is one of the mechanisms keeping the species reproductively isolated. Aquarium observers of the Bermin flock report exactly this: fish that tolerate one another in a group will turn sharply combative once a pair commits to a site, the female typically taking the lead in defending the immediate nest while the male patrols the wider territory.
Breeding
Coptodon spongotroktis is a biparental substrate (open-)spawner — the ancestral tilapiine mode, in contrast to the maternal mouthbrooding of genera such as Oreochromis and Sarotherodon. The pair deposits adhesive eggs on a cleaned hard surface and both parents then tend the clutch: fanning and guarding the eggs, shepherding the wrigglers into pits, and escorting the free-swimming fry as a guarded school. Specific wild clutch counts for spongotroktis are not well documented in the literature, but the figure is genus-typical: Coptodon substrate-spawners commonly lay on the order of several hundred to roughly a thousand eggs per spawning, scaled to female size, and the Bermin species are noted for breeding young and small. In the closely studied lake-mates, females have been recorded spawning at remarkably small sizes (a few centimetres), and both parents prove diligent guardians — a hallmark of the group. Care is biparental from egg through free-swimming fry, with the young defended vigorously until they are large enough to disperse. The combination of small body size, early maturity and committed dual-parent care is part of what has let the flock persist as nine distinct populations inside one tiny lake.
In the aquarium
The Lake Bermin Coptodon, spongotroktis among them, are kept by a dedicated circle of cichlid specialists and conservation-minded hobbyists rather than being general-trade fish, and they have a reputation as rewarding, hardy aquarium subjects. They are medium-sized and only seasonally scrappy, so a tank of around 35.5 in or more in length suits a group; the standard advice is to start with a group of six to eight juveniles and let pairs form. Out of breeding they are not aggressive toward unrelated tankmates, and they cohabit well with robust, mid-sized companions such as African tetras, larger barbs or rainbowfishes; the critical caveat is breeding, when a committed pair will fiercely defend a spawn and is best isolated, or at least given a tank divided by ample hardscape so subordinate fish can stay out of sight. Wild water parameters are undemanding — roughly 75 °F, pH near 7.5, soft and low in alkalinity — and the fish are adaptable enough that dechlorinated tap water within ordinary ranges generally suits them without special adjustment. Décor should emphasize broken sight-lines: driftwood, rockpiles, ceramic caves and inverted flowerpots both reduce squabbling and give a pair a sheltered place to spawn. Two husbandry quirks are worth flagging for this species in particular. First, plants are treated as food, not furniture — Bermin Coptodon will graze even tough Anubias and Java fern, so a permanently planted aquascape is not realistic. Second, and uniquely, spongotroktis does not forget its sponge-eating ancestry: it will nibble sponge filters, including synthetic foam, so biological filtration is best provided by a canister or hang-on-back unit rather than an exposed sponge. Diet in captivity is easy — a quality vegetable-based (mbuna-style) pellet, supplemented with blanched greens and only occasional protein-rich live or frozen foods — and the fish breed readily and make excellent parents once settled.
Conservation
Coptodon spongotroktis is assessed by the IUCN Red List as Critically Endangered, under criteria B1ab(iii)+2ab(iii); the assessment was carried out in 2009 by T. Moelants and published in 2010. The rationale is geographic: the species exists in a single lake of well under one square kilometre, so any degradation of Lake Bermin threatens the entire global population at once. The documented and potential pressures are real. Expansion of oil-palm plantations and slash-and-burn agriculture around the crater drives sedimentation and pollution into the lake, degrading the shallow substrate habitat the flock depends on. Deforestation of the crater rim could expose the sheltered water to more wind, raising the remote but catastrophic possibility of the lake's stratified layers mixing and the oxygen-poor deep water rising to suffocate the fish — and, although the lake's shallowness makes a Nyos-style CO2 burst unlikely, the broader vulnerability of Cameroonian crater lakes to limnic disturbance is part of the conservation picture. Because all nine Bermin Coptodon share this single fragile habitat, the flock has become a focus of aquarium-based conservation: the species are maintained in the hobby as C.A.R.E.S. Preservation Program fishes, and captive populations are valued as insurance against the loss of a lake that could, in principle, be erased in a single event. The species carries no CITES listing.