Taxonomy & naming
Coelotilapia joka was described in 1969 by the Belgian ichthyologist Dirk F. E. Thys van den Audenaerde, the great twentieth-century monographer of the African tilapiines, as Tilapia joka. For more than four decades it sat, like scores of other species, inside the vast catch-all genus Tilapia — a name that had become a taxonomic holding pen for almost any substrate-spawning African cichlid that was not an Oreochromis or a Sarotherodon.
That changed when Dunz & Schliewen (2013) reconstructed the molecular phylogeny of the 'haplotilapiine' cichlids and formally dismantled the old Tilapia. Their analysis placed joka on a deeply divergent, isolated branch with no close living relatives, and they erected for it the monotypic genus Coelotilapia and its own tribe, Coelotilapini. In other words, this is not a miniature cousin of the farmed tilapias at all but the last survivor of a separate, very old radiation. The Catalog of Fishes (Eschmeyer/CAS) is followed here for the valid name and authority; the parentheses on '(Thys van den Audenaerde, 1969)' record that the species is no longer in the genus in which it was first described.
Morphology
Coelotilapia joka is small by tilapiine standards, reaching about 4 in in total length — a 'dwarf tilapia' rather than the kilogram-scale food fish the name usually conjures. The body is deep and strongly compressed from side to side, with the high-backed profile typical of the group.
Its signature feature is pattern. Against a pale, silvery-to-brassy ground the fish carries a set of bold, dark vertical bars, and these are at their most dramatic in juveniles, which can be strikingly black-and-white — the look that has earned the species a devoted following among aquarists who keep it for its graphic markings rather than any bright colour. Adults are more subdued and brassy, the barring softening with age. Reported sexual dichromatism is weak and poorly documented, with the sexes broadly similar.
Habitat
The species is a narrow endemic of the Upper Guinean forest belt, confined to the lower courses of a handful of clear rainforest rivers — principally the Moa and the Moro/Mano drainages — in southern Sierra Leone and western Liberia. Within those rivers it is a fish of the bank zone, occupying the water column from mid-depth to the bottom near submerged structure.
These are warm, soft to moderately hard, near-neutral forest waters. FishBase gives an environmental envelope of roughly pH 6.0–8.0, hardness around 5–12 dH and 73–77 °F — the steady, shaded conditions of a lowland rainforest stream rather than the open, fluctuating lakes and floodplains where the larger tilapiines thrive. That restriction to a few clear-water rivers in one of West Africa's most heavily exploited forest regions is central to the species' conservation story.
Feeding
Like other members of the broader tilapiine grade, Coelotilapia joka is an omnivore that works the substrate and submerged surfaces. Its natural diet is built from aufwuchs — the carpet of algae, micro-organisms and trapped detritus that coats rocks, wood and leaf litter — together with small benthic invertebrates picked from the bottom.
In aquaria it accepts prepared foods readily and benefits from a vegetable component in the diet, in keeping with its grazing habits. As with many forest-river cichlids, a varied diet that includes some algal or plant matter supports the best colour and condition.
Mating
Coelotilapia joka is a substrate spawner, not a mouthbrooder — a distinction that matters, because the most famous African cichlids in this part of the family tree (the Oreochromis and Sarotherodon food tilapias) are mouthbrooders, while the older 'Tilapia'-grade lineages to which joka belongs retain the ancestral habit of laying and guarding eggs on a surface.
Reproduction follows the biparental pattern usual for these substrate brooders: a pair forms and defends a territory, and courtship plays out over a cleaned hard surface chosen as a spawning site. Detailed observations of pairing and courtship in the wild are sparse for this rarely studied species, and the account here reflects the well-established mode of its lineage rather than a large body of field data specific to joka.
Breeding
Spawning is biparental and substrate-based. The eggs are deposited on the cleaned surface, and both parents share guard duty — fanning and defending the clutch, then shepherding the wriggling larvae and, later, the free-swimming fry. This contrasts sharply with the maternal mouthbrooding of the farmed tilapias and aligns joka with the substrate-tending strategy of the lineage it represents.
Because the species is uncommon and localised, well-documented breeding records — clutch sizes, developmental timing, fry-rearing detail — remain limited. Where data are thin, this atlas says so rather than inventing specifics; what is secure is the substrate-spawning, biparental mode itself.
In the aquarium
Among cichlid keepers, Coelotilapia joka is prized as an oddball — a genuinely small 'tilapia' with bold barred markings and a pedigree (its own genus and tribe) that appeals to enthusiasts who value the unusual. It is kept by specialists more than beginners, and it is not a common import.
It wants clean, well-oxygenated water that mirrors its forest-river origins — warm, near-neutral and stable — along with room, cover and tolerance for the territoriality that surfaces around spawning. Given its Endangered status in the wild, captive-maintained lines carry real conservation value, and responsible aquarists who breed it help insure a species whose natural range is small and shrinking.
Conservation
Coelotilapia joka is assessed as Endangered on the IUCN Red List (2019), under criteria B1ab(iii)+2ab(iii) — the codes for a species with a very small, fragmented range that is suffering a continuing decline in the extent and quality of its habitat. It is known only from a few clear rivers of the Upper Guinean forest in Sierra Leone and western Liberia, a region under intense pressure from deforestation, alluvial and mineral mining, siltation and pollution.
What raises the stakes is the fish's evolutionary singularity. Because joka is the only species in Coelotilapia and in the tribe Coelotilapini, its loss would not merely subtract one species from a crowded genus — it would erase an entire ancient branch of the African cichlid tree. That phylogenetic distinctiveness, combined with a tiny range in a global biodiversity hotspot, makes it one of the higher conservation priorities among West African freshwater fishes.