Taxonomy & naming
Tylochromis leonensis was described in 1989 by the American ichthyologist Melanie L. J. Stiassny, in her comprehensive taxonomic revision of the genus Tylochromis published in the Annales du Musée Royal de l'Afrique Centrale (Série Sciences Zoologiques, volume 258). It was one of nine new species Stiassny erected in that monograph — a revision that doubled the number of recognized Tylochromis species from nine to eighteen at a stroke and, for the first time, imposed order on a notoriously difficult group of large, superficially similar African sand-sifters. The holotype (BMNH 1976.11.12.145) is held in the Natural History Museum, London, with an extensive paratype series distributed among the London museum, the Museum of Comparative Zoology at Harvard, the Royal Museum for Central Africa at Tervuren, and the United States National Museum. The type locality is the Taia River at Njala, in central Sierra Leone. The genus Tylochromis itself was created by Charles Tate Regan in 1920, with Pelmatochromis jentinki Steindachner, 1894 as its type species; it is the sole member of the tribe Tylochromini within the African subfamily Pseudocrenilabrinae. The genus name combines the Greek tylos, meaning knob, knot or callus, with chromis, an ancient fish name; Regan coined it in reference to a strong bony protuberance (apophysis) on the underside of the braincase that anchors the pharyngeal apparatus. The specific epithet leonensis is a place name, the Latin suffix -ensis appended to (Sierra) Leone, marking the country in which the species was first recognized. Stiassny's companion 1990 anatomical paper went further than nomenclature: weighing the genus's suspensorium, gill-arch musculature and the distinctive 'Tylochromis-type' pharyngeal apophysis, she argued that Tylochromis represents the sister group to all the remaining African Cichlidae — a single, plesiomorphic lineage branching off near the very base of the continent's cichlid tree.
Morphology
Tylochromis leonensis is a robust, moderately deep-bodied cichlid that reaches about 8.5 in in standard length, making it one of the larger fishes of its coastal-river community and a sizeable aquarium animal once tail length is added. The dorsal fin carries 13 to 15 spines followed by 13 to 16 soft rays, the anal fin three spines and seven soft rays, and there are 28 vertebrae. Several scale and lateral-line characters distinguish it within the genus: it has a high lateral-line scale count (38 to 42), with two scale rows between the upper lateral line and the anterior part of the lower lateral line, and a comparatively low gill-raker count of roughly 13 to 15 along the lower limb of the first arch. The most diagnostic feature is internal — the lower pharyngeal jaw bears a short, deep keel that is deeply indented along its ventral margin, part of the heavy molar-toothed pharyngeal mill that defines the genus. Like its congeners the fish wears the silvery, faintly iridescent flanks and dark opercular spot typical of Tylochromis; in life the genus tends toward a sandy or brassy-grey base with darker dorsal shading rather than bright colour. No specialized, contrasting breeding livery has been documented for the species, and sexual dimorphism is weak and poorly described — as in other maternal mouthbrooding Tylochromis, ripe females are recognized mainly by a fuller body and the brooding posture rather than by fixed colour or finnage differences.
Habitat
The species is restricted to the coastal river basins of the Upper Guinea ichthyological province in West Africa, an area noted for its high freshwater endemism. FishBase circumscribes its range as the coastal rivers from the Kogon in Guinea to the Bia, with the type series taken from the Taia River in Sierra Leone; the IUCN assessment additionally records it from Liberia and Côte d'Ivoire, so the species spans the Northern Upper Guinea and Southern Upper Guinea freshwater ecoregions. This Kolenta / Sierra Leone / western Liberia corridor is recognized as an exceptional pocket of freshwater endemism in its own right, sheltering a cluster of species found nowhere else — among them Sarotherodon caudomarginatus, Sarotherodon leonensis, Tilapia joka, Pelvicachromis roloffi and Anomalochromis thomasi, alongside Tylochromis leonensis itself. Within its own genus, West Africa is a minor outpost: only four of the roughly eighteen described Tylochromis occur there, against a main body of species distributed across central Africa. Two of those four, T. jentinki and T. intermedius, inhabit the same coastal rivers and may occur syntopically with T. leonensis, while the fourth, T. sudanensis, is a savannah-river species of the Niger system and the Cross and Wouri drainages further east in central Africa. These are tropical Atlantic-draining rivers that descend from the Fouta Djalon and the Guinean highlands across a narrow coastal plain, often with torrential upper courses and broader, sand-floored lower reaches fringed by floodplain lakes, swamp forest and mangrove estuaries. Tylochromis leonensis is a fish of the larger water: it inhabits extensive sandbanks in the main channels and hardly ever penetrates into small streams, behaving as a benthic species of open sandy bottoms. FishBase records a preferred temperature band of roughly 75–79 °F for the species, consistent with warm West African lowland rivers; it is regarded as an essentially Upper Guinean endemic and a strict freshwater inhabitant, though the genus as a whole tolerates the brackish lower reaches and lagoons of the same coast. As a sandbank dweller of the channel proper it occupies shallow to moderate depths over the bed, generally within the upper few metres of the water column rather than deep offshore.
Feeding
Tylochromis leonensis is a benthic macrophage — a bottom-working forager that takes in mouthfuls of substrate and sorts edible material from sand. Its diet is dominated by aquatic insects and their larvae, but it also accepts plant matter, giving it a generalist, low trophic position (FishBase estimates a trophic level of about 2.6). The genus is built around the mechanics of this lifestyle: a heavy lower pharyngeal jaw paved with stout, often molariform teeth forms a crushing mill capable of processing hard-shelled prey, and across the genus Tylochromis are well known as snail-eaters, so much so that congeners have been trialled as biological control agents against the snails that host schistosomiasis. In leonensis the pharyngeal apparatus is robust but its dentition is comparatively modest by the standards of the most specialized mollusc-crushers, in keeping with a diet weighted toward insect larvae rather than thick-shelled gastropods. Working the open sandbanks of the river channel, it fills the role of a sand-sifting invertivore in its community, recovering chironomids and other benthic invertebrates from the sediment of large West African rivers.
Mating
Reproductively, Tylochromis leonensis follows the genus pattern of a maternal mouthbrooder that does not form a pair bond. There is no enduring partnership between male and female and no shared, jointly defended territory of the kind seen in substrate-spawning cichlids; instead, mating is a brief encounter, after which the sexes part and the female alone assumes the entire burden of brood care. Detailed in-situ courtship observations for this particular species are lacking, but in mouthbrooding cichlids of this reproductive style spawning is typically initiated by a male displaying over a patch of the sandy bottom, with a receptive female approaching to spawn before withdrawing with the clutch. The absence of pair-bonding and biparental territoriality is itself the salient social fact about the species: outside the moment of spawning, adults are not tied to a mate, and the female's investment is concentrated entirely into oral incubation rather than into defending eggs laid on a substrate.
Breeding
The species is described as oviphilous and as a maternal mouthbrooder: after spawning the female takes the fertilized eggs into her mouth and broods them orally through incubation and early larval development, releasing free-swimming fry only once they are well advanced. The male contributes nothing to care beyond fertilization. No clutch count has been published specifically for Tylochromis leonensis, and at roughly 8.5 in it is a large fish for its genus; mouthbrooding Tylochromis are generally moderately fecund relative to their size, producing clutches on the order of a few dozen to perhaps a couple of hundred comparatively large eggs, the trade-off inherent in oral incubation, where brood size is physically limited by the volume of the female's buccal cavity. The genus is rated as highly resilient by FishBase, with an estimated minimum population doubling time of under fifteen months, implying that under good conditions recruitment is rapid despite the modest per-spawning egg numbers. Wild spawning has not been documented in detail, and there is no published aquarium breeding report for the species, so the finer points of egg number, incubation period and fry size remain to be established.
In the aquarium
Tylochromis leonensis is essentially an ichthyologist's fish rather than a hobby staple — it is rarely imported, has no established trade common name, and PlanetCatfish records no breeding report and no documented aquarium keepers for it. Anyone who does encounter it should plan around what it is: a 20-plus-centimetre, sand-sifting West African river cichlid that needs a large, long tank with a substantial open footprint rather than height. A deep bed of fine sand is non-negotiable for a fish whose entire feeding biology is built on mouthing and sorting substrate; coarse gravel both frustrates that behaviour and risks abrading the gills. Strong, well-oxygenated water with good flow suits a fish of flowing coastal rivers, and powerful mechanical and biological filtration is needed to cope with the detritus a sand-sifter stirs up. Water should be warm — around the documented 75–79 °F preference, and up toward the high 20s is reasonable for a lowland tropical species — and kept in the broadly neutral to slightly alkaline, moderately soft to medium-hard range typical of these rivers (roughly pH 6.5 to 8.0). Feeding is straightforward given its generalist, insect-larva-based wild diet: sinking foods, frozen and live invertebrates such as bloodworm, and some plant or vegetable matter will all be taken. As a large, robust, non-territorial mouthbrooder it is best matched with similarly sized, sturdy tankmates that can share open water without being bullied or, conversely, harassing it; it is not a community fish for small, delicate species. The honest summary is that husbandry guidance here is extrapolated from the genus and from its known biology — there is little first-hand aquarium literature to draw on for this species specifically.
Conservation
Tylochromis leonensis is assessed by the IUCN Red List as Least Concern, in an evaluation published in 2020 (assessed 10 January 2020 by I. Diallo and P. Lalèyè). The assessment records the species across four West African countries — Guinea, Sierra Leone, Liberia and Côte d'Ivoire — notes a population trend that is presently unknown, and identifies no current widespread threats to the species, the basis for the Least Concern listing. It carries no CITES listing and no CMS listing. That comparatively comfortable status should be read against the broader pressures on the Upper Guinea coastal rivers it depends on, a region of exceptional but vulnerable freshwater endemism. Across these basins, mangrove clearance, dam construction (for example on the Konkouré in the Northern Upper Guinea ecoregion), deforestation, mining and the general intensification of land use are degrading aquatic habitat and have placed a number of co-occurring endemic fishes at risk. As a wide-ranging, large-river generalist, Tylochromis leonensis is far less exposed than the narrow-range endemic killifishes and barbs of the same region, but it shares their watershed, and the long-term health of its populations is tied to the fate of these Atlantic coastal rivers.