Taxonomy & naming
This page exists to set a name straight rather than to describe a species. The epithet traces to Albert C. L. G. Günther's 1903 paper "Last account of fishes collected by Mr. R. B. N. Walker... on the Gold Coast" (Proceedings of the Zoological Society of London 1902, vol. 2: 333, pl. 31), where he erected Chromis multifasciatus on material from "Lake Busum-chi" — Lake Bosumtwi, Ghana. The syntypes are lodged in the Natural History Museum, London (BMNH 1903.4.24.42–51) and the US National Museum (USNM 50954, 86647). Eschmeyer's Catalog of Fishes lists the current status of Chromis multifasciatus unambiguously as a synonym of Sarotherodon galilaeus (Linnaeus, 1758), the mango tilapia, while noting that several authorities (Trewavas & Teugels 1991; Teugels & Thys van den Audenaerde 1992; Dankwa et al. 1999) retained it as a valid subspecies. In Trewavas's 1983 monograph on the tilapiine genera Sarotherodon, Oreochromis and Danakilia, the Bosumtwi fish is treated as Sarotherodon galilaeus multifasciatus — one of five recognized subspecies of Sarotherodon galilaeus and the form endemic to that crater lake. Genus matters here: Sarotherodon is a biparental (predominantly paternal/dual) mouthbrooder, whereas the genus Tilapia in the modern sense is a guarder of substrate-laid eggs. Calling this fish a "Tilapia" therefore mis-states not just its name but its entire reproductive biology. The binomial "Tilapia multifasciata" is not a recognized valid combination; FishBase explicitly flags "Tilapia multifasciata (non Günther 1903)" as a misapplied name, and the only defensible modern usage is Sarotherodon galilaeus, or — if the Bosumtwi population is named — Sarotherodon galilaeus multifasciatus. The descriptions that follow are of that real fish.
Morphology
Sarotherodon galilaeus is a deep-bodied, laterally compressed cichlid; FishBase gives a maximum of about 15.5–16 in total length and 1.6 kg for the species across its huge range, but these figures come from large open-water populations and bear little resemblance to the dwarfed Bosumtwi form. In the crater lake the fish is small: seine sampling by Obirikorang et al. (2020) recorded mature Sarotherodon galilaeus averaging only about 3 in standard length (3.5 in total length) and roughly 17 g, smaller even than adults of most of the lake's other native cichlids. Meristically the species carries 14–17 dorsal spines and 11–14 soft rays, three anal spines and 9–12 anal soft rays, and 27–31 vertebrae; the snout profile is straight to slightly arched and the body depth is typically 45–56% of standard length. Coloration is muted — greyish dorsally, silvery below, with pinkish margins to the dorsal and caudal fins in reproductive individuals; the "many-banded" sense of multifasciatus refers to the vertical barring shown by some specimens, though Trewavas noted that distinct melanin patches occur only in occasional fish rather than across whole populations. Sexual dimorphism is slight: the species lacks marked breeding dichromatism, but males develop somewhat longer soft dorsal- and anal-fin rays.
Habitat
Lake Bosumtwi is the type locality and the home of the multifasciatus form. It is a roughly 5 mi-wide, closed meteorite-impact crater lake near Kumasi in the Ashanti Region of Ghana — the only substantial natural lake in the country and one of the youngest and best-preserved complex impact craters on Earth (formed about 1.07 million years ago). The basin has an internal-drainage pattern with 37 inflowing streams (five permanent) and no outflow, and reaches a maximum depth near 256 ft (Whyte 1975; Turner et al. 1996). Because it is endorheic and deep, the lake is seasonally stratified and its lower waters are anoxic, so fish life is confined to the oxygenated upper layer and the shoreline shallows. Whyte's (1975) survey recorded eleven historical fish species in the basin, of which five are cichlids — Tilapia busumana, Coptodon discolor, Sarotherodon galilaeus, Hemichromis fasciatus and Chromidotilapia guntheri — with a sixth, Hemichromis frempongi, endemic to the lake. Across its wider African and Levantine range, Sarotherodon galilaeus is a demersal fish of shallow inshore lake waters and rivers, recorded from depths of about 16 ft and upward, in the temperature band of roughly 72–82 °F (it has been found as cold as 48 °F). In Bosumtwi the mouthbrooding planktivores are nonetheless tied to the shallows: Whyte noted that the need to spawn over firm substrate, plus the surface-feeding habits of the juveniles, keeps even the open-water feeders dependent on the shallow zone.
Feeding
Sarotherodon galilaeus is a low-trophic-level microphage — FishBase estimates a trophic level near 2.0. Adults feed mainly on phytoplankton and fine organic detritus, filtering suspended algae and particulate matter, and the IUCN assessment describes the species as planktivorous and phytophagous, also taking some crustaceans, functioning as an obligate particulate feeder as larvae and juveniles and largely as a filter feeder as an adult. In the Sudd lakes it is often associated with beds of submerged vegetation. In Lake Bosumtwi this trophic role is central to how the lake works: Whyte (1975) characterized Sarotherodon galilaeus there as one of two mouthbrooding planktonic feeders exploiting the open-water food supply, in contrast to the substrate-associated and predatory native cichlids. As a fine-particle grazer near the base of the food web, the Bosumtwi mango tilapia is forage as much as forager, and its biomass helps support the lake's modest artisanal fishery.
Mating
Reproduction in Sarotherodon galilaeus is unlike anything in the substrate-spawning Tilapia for which this fish is sometimes mistaken. The species forms only temporary pair bonds and shows little or no breeding dichromatism. Courtship and territory establishment are led predominantly by the female: she takes the initiative through courting and mating, and is mainly responsible for excavating the spawning pit and defending the mating territory — a reversal of the more familiar tilapiine pattern. Pair formation persists just long enough for spawning; once the eggs are taken into the parents' mouths the bond dissolves. The species occasionally schools and can be territorial during reproduction, with juveniles and breeding adults gathering inshore while non-breeding adults range into open water. In the confines of Lake Bosumtwi, where suitable firm substrate is limited to the shallow margins, these inshore-spawning requirements concentrate breeding into the narrow shoreline band the lake's fishes share.
Breeding
Sarotherodon galilaeus is a biparental mouthbrooder — the defining trait of its genus and the single most important reason "Tilapia multifasciata" is a misnomer. After the female-led courtship, eggs are laid in a shallow pit and fertilized, then taken up and incubated orally; both sexes participate in mouthbrooding, though it is often the male (or both parents) that carries the developing clutch, with the female more rarely doing so (Daget & Iltis 1965, via the IUCN assessment). This dual oral incubation contrasts sharply with the maternal-only mouthbrooding of Oreochromis and with the open substrate-guarding of Tilapia and Coptodon. Published clutch sizes specific to the Bosumtwi form are not well documented, but Sarotherodon galilaeus is a low-fecundity mouthbrooder by tilapiine standards — fecundity figures above 1,000 eggs are cited for the species generally, far below the many-thousand-egg clutches of substrate-spawning tilapias, and Obirikorang et al. (2020) single out the low fecundity of the lake's native mouthbrooders as a key vulnerability. Brooded young are released as free-swimming fry that shelter near the parents and the shallow substrate. Because incubation is oral, the brood is independent of nest sites once spawning is complete, but the surface-feeding habit of the juveniles still binds them to the lake's shallow zone.
In the aquarium
Practically speaking, there is nothing to keep under the name "Tilapia multifasciata" — the name is invalid and no fish is traded as such. The underlying species, Sarotherodon galilaeus, is a commercial food and aquaculture fish rather than an ornamental one; it appears in the aquarium trade only marginally, usually as the nominate form or as undifferentiated "mango tilapia," not as the Bosumtwi subspecies. Anyone who did keep Sarotherodon galilaeus would be housing a large, plain, fast-growing tilapiine that wants warm water (roughly 72–82 °F), tolerates a wide chemistry, and needs a big tank or pond; it is a microphagous filter-feeder, so it accepts prepared and vegetable foods readily, and its biparental mouthbrooding can be observed but offers little of the colour or compact size hobbyists seek. The endemic Bosumtwi form in particular has no place in the hobby: it is a small, geographically restricted population of conservation interest, not an aquarium subject, and removing fish from a closed crater lake under pressure would be irresponsible. In short, treat this entry as a nomenclatural correction — if you are looking for a fish, you want a validly named species, not this combination.
Conservation
The Bosumtwi form has no separate IUCN assessment of its own as a valid species; its status is read through its parent, Sarotherodon galilaeus, which the IUCN Red List assesses as Least Concern (assessed 23 April 2020; Diallo et al. 2020, version 2025-2), on the grounds of a very wide West African, Nilotic and Levantine range with no major widespread threats. That basin-wide security, however, says little about the crater-lake population. Lake Bosumtwi is a small (~5 mi), closed, endorheic system — a UNESCO Biosphere Reserve since 2016 and a culturally sacred lake — whose endemic and near-endemic cichlids have low fecundity and are already exposed to mounting artisanal fishing pressure from the lakeside communities. The most acute recent threat is biological: after an unpermitted Nile-tilapia (Oreochromis niloticus) cage farm operated on the lake from 2012 until its closure in 2015, Obirikorang et al. (2020) documented the first established wild Oreochromis niloticus in Bosumtwi, making up 2–10% of cichlid catches. A high-fecundity, environmentally tolerant invader in so confined a basin poses real risk of competition with, and displacement of, the lake's small native mouthbrooders — the mango tilapia among them. So while the species as a whole is Least Concern, the Bosumtwi multifasciatus population should be read as a vulnerable endemic form in a stressed closed lake, not as a fish of no conservation concern.