Taxonomy & naming
The Tholloni tilapia was described in 1884 by the French ichthyologist Henri-Émile Sauvage as Chromis tholloni, in the Bulletin de la Société Zoologique de France, from material collected at Franceville on the upper Ogooué River in Gabon. The original type series comprises syntypes held at the Muséum national d'Histoire naturelle in Paris (MNHN 1884-0294, 0295 and 1884-098), one of which (1884-298) was later treated as a holotype in the museum's type catalogues. For most of the twentieth century the species was carried under the catch-all genus Tilapia, and the combination Tilapia tholloni was the standard usage following the influential tilapiine revisions of Teugels and Thys van den Audenaerde. The genus Coptodon, originally a Gosse name long sunk into Tilapia, was resurrected as a valid genus by Andreas Dunz and Ulrich Schliewen in their 2013 molecular phylogeny of the haplotilapiine cichlids 'formerly referred to as Tilapia,' which broke the unwieldy old Tilapia into several genera along lineage lines. In that scheme Coptodon gathers the West and Central African substrate-spawning tilapiines — among them the familiar Coptodon zillii and Coptodon rendalli — and tholloni was formally moved to it as Coptodon tholloni (Sauvage, 1884), the combination now accepted by the Catalog of Fishes and subsequent regional treatments. Genetically it sits very close to Coptodon zillii; electrophoretic work (Sodsuk 1993) found the two almost indistinguishable, and the species is one of the better-studied members of the genus.
Morphology
Coptodon tholloni is a modest-sized, fusiform-to-deep-bodied tilapia. FishBase gives a maximum of about 8.5 in total length, but most individuals — and virtually all aquarium fish — are considerably smaller, which is why the species earns the loose hobby label 'dwarf tilapia' relative to the half-metre giants of the genus Oreochromis. The fin counts are typical of the genus: 15 to 16 dorsal spines and 9 to 11 soft rays (24 to 26 total dorsal elements), three anal spines with 7 to 9 soft rays, and 27 to 29 scales along the lateral line. The mouth is terminal and the outer-row jaw teeth are relatively fine. Diagnostic colour features set it apart from its congeners: the unpaired fins are not predominantly red-brown; the caudal fin is densely scaled and patterned with a network of clear spots and lines; there is at least one (sometimes two) row of dark spots running along the middle of the flank; and each flank scale carries a small black sickle-shaped mark at its base, producing a fine speckled overlay across the body. The lower limb of the first gill arch bears ten or fewer rakers — a comparatively low count that reflects the species' coarse, plant-based diet rather than fine filter-feeding. Sexual dimorphism is modest and typical of substrate-spawning tilapiines: ripe females become noticeably rounder in the belly, and breeding fish of both sexes intensify in colour, but the sexes are not strongly differentiated outside the spawning season and are most reliably told apart by venting.
Habitat
The species is a fish of the coastal river basins of Lower Guinea and the lower Congo region of west-central Africa. Its documented range runs from the Ogooué River in Gabon — the drainage of the type locality — south through the Nyanga (Gabon), the Kouilou-Niari in the Republic of the Congo, and the Chiloango on the Angola–Democratic Republic of the Congo border, to the lower Congo River itself in the DRC. Specimens from Pool Malebo (Stanley Pool) on the Congo are ambiguous and may represent either this species or the closely allied Coptodon congica. Most of this range falls within the Ogooué–Nyanga–Kouilou–Niari freshwater ecoregion, with the lower-Congo populations reaching into the Lower Congo ecoregion. It is a strictly freshwater, benthopelagic fish of warm tropical lowland waters; FishBase cites a preferred temperature band of roughly 75–79 °F, and as a coastal-rivers species it occupies vegetated margins, swamps, floodplain wetlands and slow reaches rather than open rapids. The IUCN classifies its habitat simply as inland wetlands. Like other Coptodon it tolerates a fairly broad chemical envelope and is at home in soft, slightly acidic to near-neutral coastal-forest waters; well-oxygenated, weedy shallows where macrophytes and algae are abundant are its characteristic biotope.
Feeding
Coptodon tholloni is a herbivore — a macrophyte- and algae-eater that sits low on the food web, with FishBase placing its trophic level at about 2.6. Like its close relative Coptodon zillii, it is a chopping, plant-shredding tilapiine: the genus name itself (from the Greek for 'cut' and 'tooth') advertises the cutting dentition these fish use to bite and tear filamentous algae, soft aquatic plants and other vegetable matter, supplemented opportunistically with detritus and small invertebrates. Its relatively low gill-raker count is consistent with a coarse plant diet rather than the fine plankton-straining of mouthbrooding tilapias. This vegetarian habit is precisely why substrate-spawning tilapias of the zillii–rendalli–tholloni group have been valued in aquaculture and pond management — they crop nuisance weed and algae — and tholloni in particular has been used extensively as a laboratory model in tilapia nutrition and physiology studies. In the wild community it functions as a grazer of the weedy shallows, helping convert macrophyte and periphyton production into fish biomass available to larger predators.
Mating
In contrast to the maternal mouthbrooders that dominate the tilapia of aquaculture, Coptodon tholloni is a monogamous, pair-bonding substrate spawner, and pair formation is the centrepiece of its reproductive behaviour. A male and female form a bond and jointly establish and defend a territory on the bottom, where they prepare a spawning site by cleaning a firm surface or excavating a shallow depression in the substrate. Courtship and territorial defence are mutual, with both partners driving off intruders, and the bond persists through spawning and into an extended period of shared brood care. This biparental, territorial system — the ancestral condition for the genus — makes the species comparatively transparent to observe and is part of why substrate-spawning Tilapia (in the old broad sense) including tholloni became classic subjects for studies of cichlid pair-bonding and parental behaviour. The pre-spawning phase is one of site selection, surface cleaning and steadily escalating site fidelity rather than the lek-style display of mouthbrooding tilapiines.
Breeding
Coptodon tholloni is an open, pair-bonding substrate brooder in which both parents guard the brood. The pair deposits a sheet of adhesive eggs on a cleaned hard surface or in a prepared depression, after which the eggs are guarded and fanned by the parents in place rather than carried in the mouth. The eggs are small for a tilapia — measured at roughly 0.5 in in the tilapia-culture literature, markedly smaller than the 0.5 in eggs of mouthbrooding Oreochromis — which is a typical trade-off: substrate spawners lay more, smaller eggs and protect them externally, whereas mouthbrooders lay fewer, larger eggs and shelter them orally. Wild clutch sizes are not precisely tabulated for tholloni itself, but congeneric open substrate-spawners in the genus are highly fecund (large Coptodon zillii may release on the order of a thousand eggs per spawn), and tholloni's small egg size and 'High' resilience rating (a minimum population-doubling time under fifteen months) point to a similarly prolific output. After hatching, the wrigglers are tended by both parents and the free-swimming fry are guarded as a shoal that the adults herd and defend; the young begin taking outside food within roughly a week of becoming free-swimming. The biparental guarding of mobile young, rather than oral incubation, is the defining feature of the species' breeding biology.
In the aquarium
The Tholloni tilapia is kept only occasionally in the hobby, usually by tilapiine and African-cichlid specialists rather than general community keepers, and is sometimes traded as a 'Tholloni tilapia' or grouped with the small substrate-spawning species marketed as 'dwarf tilapia.' It is an undemanding, hardy fish — qualities that made it a stalwart of laboratory and pond use — but two facts govern its husbandry: it grows to a stout 20-plus centimetres, and it is a dedicated plant-eater. A single pair needs a robustly filtered tank of at least about 40 US gal (a 47 in / 4-foot footprint is sensible for adults), with plenty of bottom area, because a bonded pair becomes strongly territorial when in breeding condition and will commandeer a large patch of the floor.
Décor should be simple and durable: a sand or fine-gravel substrate the fish can work, some flat stones or slate to serve as spawning surfaces, and sturdy rockwork or terracotta to break sightlines. Do not expect a planted aquarium to survive — as a macrophyte grazer the species will crop and uproot soft plants, so any greenery should be tough (Anubias, Java fern lashed to wood) or regarded as food. Water chemistry is forgiving within the warm tropical range: a temperature of roughly 75–82 °F suits it, with pH anywhere from about 6.0 to 7.8 and soft-to-moderately-hard water all acceptable, reflecting the broad coastal-rivers envelope of the genus. Good filtration and regular water changes matter more than precise parameters; these are messy, well-fed herbivores.
Feeding is easy and is the key to colour and condition: a vegetable-led diet of spirulina and algae-based pellets or flake, blanched greens (spinach, courgette, peas) and the occasional frozen or live invertebrate treat keeps them in good order. Avoid a purely high-protein carnivore diet, which does not suit a grazing tilapiine.
Tankmate choice is the usual tilapia compromise. Outside breeding the species is reasonably even-tempered for its group, but a spawning pair is territorial and will defend the nest vigorously, so companions should be robust, similarly sized fish that can keep out of the way — other medium African cichlids, large barbs or catfish in a spacious tank. Small or timid fish are a poor match, and keeping multiple unpaired adults in close quarters invites the chronic squabbling typical of substrate-spawning tilapias. Its real appeal is behavioural: a settled pair raising and shepherding a cloud of fry is one of the more rewarding sights in tilapiine keeping.
Conservation
The IUCN Red List assesses Coptodon tholloni as Least Concern (assessed 16 February 2009 by T. Moelants, published in the 2010 assessment), recording it from Gabon, the Republic of the Congo and the Democratic Republic of the Congo, with an unknown population trend and no known major threats. As a widespread, adaptable habitat generalist of coastal-river wetlands — and a hardy, fast-reproducing herbivore rated 'High' for resilience and only slightly vulnerable to fishing — it is far less exposed than the many narrow-range endemic tilapias of West and Central African crater lakes, several of which are gravely threatened. It carries no CITES or CMS listing and is considered harmless to humans. The species is of minor local fisheries and aquaculture value rather than a conservation concern. The broader caution is regional rather than specific: the coastal rivers and lower-Congo basin it inhabits face the familiar pressures of deforestation, expanding agriculture, pollution and habitat alteration, but none of these is currently documented as a population-level threat to this particular tilapia.