Taxonomy & naming
Tylochromis microdon was described by the British ichthyologist Charles Tate Regan in 1920, in the Annals and Magazine of Natural History, from specimens collected at Bikoro on Lake Tumba in what was then the Belgian Congo. The genus Tylochromis had itself been erected by Regan in the same era to hold a group of large, deep-bodied African cichlids with distinctive sand-sifting jaws and swollen sensory canals on the head. The type series rests in the Natural History Museum, London; the lectotype (BMNH 1899.11.27.74) was fixed much later by Melanie Stiassny in her landmark 1989 revision of the genus, with paralectotypes registered alongside it. Stiassny's monograph — 'A taxonomic revision of the African genus Tylochromis (Labroidei, Cichlidae)' — remains the foundational treatment of the group and the single most important reference for this species; it confirmed microdon as valid and worked out its anatomy in detail. Within the cichlid family Tylochromis sits in the subfamily Pseudocrenilabrinae (the African cichlids), and the genus is often placed in its own tribe, the Tylochromini, regarded as an early-branching lineage near the base of the African cichlid radiation. The species epithet microdon, 'small-tooth', refers to the fine pharyngeal dentition Regan noted when he diagnosed the fish. A report of the species from neighbouring Lake Mai-Ndombe is regarded as questionable — most likely an error in the locality label — leaving Lake Tumba as its only confirmed home.
Morphology
Tylochromis microdon is a modest-sized cichlid by the standards of its genus, reaching about 6 in in standard length — well short of the 10 in or more attained by the largest river-dwelling Tylochromis. The body follows the genus plan: deep, laterally compressed, with a steeply sloping forehead and a fairly small, low-set, slightly subterminal mouth suited to working the bottom. Fin counts run to 14–15 dorsal spines and 12–15 soft dorsal rays, 7 anal soft rays, and 28–29 vertebrae. Stiassny diagnosed the species on a suite of head features rather than colour: a marked hypertrophy (swelling) of the lateral-line canals on the flank and onto the caudal fin, strikingly inflated laterosensory canals on the preopercle, and a distinctive excavation of the premaxillary oral valve. The 'small-toothed' name comes from the lower pharyngeal jaw, which carries numerous fine, slender, bicuspid teeth — a comparatively delicate pharyngeal mill set against the heavier, snail-crushing dentition seen in some of its congeners. As is typical of the genus and of African cichlids generally, no strong external sexual dimorphism has been documented; the sexes are not reliably told apart by size or colour in the available material, and like other Tylochromis it is a maternal mouthbrooder in which the female alone carries the brood.
Habitat
Lake Tumba is the entire world of this species. The lake is a shallow blackwater body of roughly 765 square kilometres lying almost on the equator in the central Congo basin (the Cuvette Centrale), connected to the Congo River by a single channel and surrounded by a wide belt of seasonally and permanently flooded swamp forest. It is strikingly shallow — averaging only three to five metres deep, with a maximum around eight metres — yet well oxygenated from top to bottom because strong winds keep the water column churned. The water is extremely soft and acidic: dissolved-mineral content is very low, and recorded pH values run as low as 4.0–4.9, the lake's food web resting largely on leaf litter and organic matter washed in from the surrounding forest rather than on in-lake plankton. What sets Tylochromis microdon apart is that it is, unusually for the genus, a predominantly lacustrine fish: Stiassny found it restricted to the open lake proper and absent from the bordering swamps and inundated forest where many other Congo fishes breed and feed. Most members of Tylochromis are creatures of flowing rivers and channels, so this commitment to a still, shallow lake is one of the more distinctive facts about the species.
Feeding
Tylochromis microdon is a benthic microphage — a bottom-grubbing fish that takes small food rather than large prey. It feeds mainly on small organic particles, plant material and invertebrates worked out of the soft lake-bed sediments, sitting low on the food web at a trophic level estimated around 2.8. This fits the broader feeding biology of the genus, which is built around sand-sifting and bottom-grubbing: Tylochromis take mouthfuls of substrate and sort edible particles from sand and detritus, and several congeners are equipped to crush snails on their pharyngeal jaws. In microdon, however, the lower pharyngeal teeth are fine and slender rather than heavy and molariform — the 'small-tooth' condition that gives the fish its name — which points to a diet of soft, fine material and small invertebrates rather than hard-shelled molluscs. In Lake Tumba, where the food chain is fuelled by allochthonous organic matter shed from the encircling swamp forest, a microphagous bottom-sifter has a ready and abundant resource in the soft, detritus-rich sediments of the lake floor.
Mating
Reproduction in Tylochromis microdon follows the genus pattern of maternal mouthbrooding without a lasting pair bond. Unlike the substrate-spawning, biparental cichlids of the New World, the sexes here do not form a stable couple to share parental duties; instead mating is brief, and the female alone takes on the care of the brood. This is the same reproductive strategy seen across the African mouthbrooding cichlids, in which males typically court and spawn with one or more females and then play no further role, while each female withdraws to incubate her clutch in her mouth. Detailed in-situ courtship observations for this particular species have not been published — Lake Tumba's fish fauna remains poorly studied — so the fine points of how males display, where spawning takes place on the lake bed, and how territories (if any) are held are not documented. What is reliably recorded is the essential fact: microdon is a maternal mouthbrooder that does not pair bond, and the burden of reproduction falls on the female.
Breeding
As a maternal mouthbrooder, the female Tylochromis microdon collects her eggs into her mouth at or shortly after spawning and broods them there through hatching and the early free-swimming stage, the developing young sheltered inside the buccal cavity until they are large enough to fend for themselves. This oral incubation trades a large clutch for greater safety per egg — a hallmark of the African lacustrine cichlids and a reproductive mode shared across the genus Tylochromis. Specific fecundity figures for microdon have not been published, but the genus-typical pattern for mouthbrooding Tylochromis is a comparatively modest clutch on the order of a few dozen to perhaps a hundred or so relatively large eggs, far fewer than a substrate-spawner of similar size would lay. No captive or field breeding account documents clutch size, incubation period, or fry development for this species in particular; like much of Lake Tumba's biology, its breeding cycle has gone largely unstudied. In the lake's warm, acidic, equatorial water the broad seasonal flood pulse — a small flood around May–June and a larger one from September into January — is the kind of environmental cue that drives spawning in many central Congo fishes, and is the most plausible trigger here.
In the aquarium
Tylochromis microdon is essentially never seen in the aquarium hobby. It is an obscure, single-lake endemic with no ornamental trade, no established captive population, and — being assessed as Endangered — no case for casual collection. Almost everything written here is therefore inference from its biology rather than from keeping experience, and it should be read that way.
Were it ever maintained, the demands would be specific. This is a fish of warm, extremely soft, strongly acidic blackwater (Lake Tumba runs to pH 4–5), so it would need soft, acidic conditions well outside the comfort zone of most rift-lake cichlids and tap-water setups. It is a dedicated bottom-sifter, so a deep bed of fine, soft sand is non-negotiable — coarse gravel would frustrate its natural feeding and risk gill abrasion. At roughly 6 in and built on the deep-bodied Tylochromis plan, an adult would want a long tank with a generous footprint and open sand to work, gentle to moderate flow, and the dim, tannin-stained water of its native lake. Feeding would be straightforward in principle, since it is an unfussy microphage that takes small invertebrates, detritus and plant matter; a varied diet of small frozen and prepared sinking foods would suit it. As a non-pair-bonding maternal mouthbrooder it would likely be best kept as a group with enough space to diffuse aggression, but none of this is documented in practice. In short: a specialist's fish in theory, and in reality one that almost no aquarist will ever encounter.
Conservation
The IUCN Red List assesses Tylochromis microdon as Endangered, under criterion B1ab(v); the assessment was carried out on 16 February 2009 by T. Moelants and published in 2010. The category reflects the species' tiny range: it is endemic to a single, roughly 765-square-kilometre lake, and a fish confined to one small water body is inherently exposed — a single catchment-wide disturbance can affect the entire population at once. The IUCN review of freshwater biodiversity in central Africa flags Lake Tumba as harbouring several endemic and threatened fishes, listing both Tylochromis microdon and the lacustrine cichlid Lamprologus tumbanus as Endangered, alongside other lake specialists. The pressures on the Lake Télé–Lake Tumba wetland complex are the familiar ones of the Congo basin: expanding human settlement and fishing pressure on a productive shallow lake, deforestation and disturbance of the surrounding swamp forest that supplies the lake's food web, and the prospect of climate-driven changes to the central basin's flood regime. The fish fauna of Lake Tumba has been little studied since mid-twentieth-century surveys, so population trends are poorly known — itself a conservation concern, since a narrow-range endemic can decline unnoticed. Its long-term security rests on the health of one lake and the forested wetlands that feed it.