Taxonomy & naming
Clarias gariepinus was described by the English naturalist William John Burchell in 1822 from the Gariep (Orange) River in South Africa, the source of its specific epithet. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Clarias gariepinus as the valid name. It belongs to the family Clariidae, the walking catfishes and airbreathing catfishes, within the order Siluriformes.
The genus Clarias is large and taxonomically complex, encompassing scores of species across Africa, the Middle East, and South and Southeast Asia. Over its history the African sharptooth catfish has appeared in the literature under various earlier combinations and synonyms, but Clarias gariepinus has been stable as the accepted name for the widespread African taxon. Some earlier African literature used the name Clarias lazera, which is now treated as a junior synonym.
The epithet gariepinus is a Latinised form of 'Gariep', the Khoikhoi name for the Orange River and historically the name used for that drainage in the Cape region of southern Africa.
Morphology
The African sharptooth catfish is an elongate, powerfully muscled fish with a broad, depressed head and a wide, terminal mouth armed with bands of small, conical teeth. The body is laterally compressed toward the tail and covered with smooth, scaleless skin — entirely naked, with no bony plates or scutes. Four pairs of barbels surround the mouth: one maxillary pair, two mandibular pairs, and one nasal pair. The dorsal fin is long and low, running most of the length of the body; both the dorsal and pectoral fins bear stiff, serrated spines that lock erect and can tangle badly in a net, and can jab the keeper hard enough to cause injury.
Adult coloration is typically grey to dark olive-brown on the back and flanks, fading to a pale cream or white on the belly; the skin sometimes has a faint mottling. The suprabranchial organ — a paired, branching structure in the gill chamber — allows the fish to extract oxygen from air and is visible as a slight swelling behind the head in live specimens.
FishBase records a maximum total length of 78.5 in, though most wild fish are 31.5–51 in; farm-raised individuals rarely exceed 39.5 in. This is a genuinely large catfish.
Habitat
Clarias gariepinus has one of the widest natural distributions of any African freshwater fish: it occurs across nearly all of sub-Saharan Africa, from the Nile and Senegal river systems south through the Congo basin to the Orange River in South Africa, including the Rift Valley lakes (as a peripheral species), the Niger, the Volta, the Zambezi, and many smaller systems. It has also been introduced widely — and become invasive — in parts of Asia, the Middle East, southern Europe, and beyond.
It is a habitat generalist of remarkable range. It thrives in large rivers, floodplain lakes, swamps, irrigation channels, and ephemeral pools. Its suprabranchial air-breathing organ allows it to inhabit waters so warm and stagnant that dissolved oxygen plummets to near zero — conditions lethal to most other fish. It tolerates temperatures from about 68 °F to 82 °F and a wide pH range of roughly 6.0 to 8.0, in soft to moderately hard water. It can move overland through wet grass at night, which is how it colonises new water bodies and how it earned the 'walking catfish' label (though it is less agile overland than the true walking cats of Southeast Asia).
Feeding
Clarias gariepinus is a generalist carnivore and opportunistic piscivore. In the wild it eats fish, frogs, crustaceans, aquatic invertebrates, carrion, and organic detritus — essentially anything organic that it can locate by scent or with its sensitive barbels. Larger individuals are dominated by fish in their diet and will pursue prey up to a substantial fraction of their own body length.
In the aquarium or pond context this translates to a fish that will eat any tankmate it can fit in its mouth. Suitable foods include large whole fish or fish fillets, prawns and shrimp, earthworms, and large sinking pellets formulated for carnivorous catfish. Feeding is most active after dark, as this is a nocturnal species that spends the daylight hours sheltering in cover. Because of its size, an individual in a tank will consume large quantities of food and produce proportionately heavy waste loads.
Mating
In the wild, Clarias gariepinus spawns seasonally, typically triggered by rising water levels and increased rainfall at the onset of the wet season. Males develop a distinctly swollen genital papilla during breeding condition; females become visibly gravid with eggs. Spawning is broadcast-style over flooded vegetation and substrate, with no extended courtship ritual described for the species.
The separation of the sexes is clearest during reproductive condition: sexually active males reach maturity at a smaller size than females in farm practice — roughly 31.5 in for males versus 39.5 in or more for productive females — though individuals well below those sizes have been observed in sexual condition under farm conditions. In commercial production, broodstock are selected by size and condition, and mating is initiated artificially.
Breeding
Clarias gariepinus is bred at enormous commercial scale on fish farms across Africa and Asia, where it is a major aquaculture species farmed for food. Commercial reproduction invariably involves hormone-induced spawning: broodstock fish are injected with pituitary extract or synthetic gonadotropin-releasing hormone analogues (such as Ovaprim), eggs are stripped from ripe females, and milt from males is used to fertilise them artificially, after which the eggs are incubated in hatchery troughs.
This is not a species that reproduces in the home aquarium. The combination of very large adult size (well over 39.5 in for reproductive individuals), the need for hormone induction to trigger spawning under captive conditions, and the logistical requirements of artificial fertilisation and hatchery incubation puts home breeding entirely out of reach. Aquarists should not expect or attempt it. The fish encountered in the hobby are farm-raised juveniles produced through this commercial pipeline.
In the aquarium
The African sharptooth catfish is a serious commitment, and the vast majority of individuals sold in the aquarium trade are purchased without any appreciation of what the fish will become. A juvenile of 4–6 in is appealing enough in a pet shop; the same animal at 31.5–39.5 in is a public-aquarium or pond fish that has long since eaten every tankmate it could swallow and demolished any décor in the tank. This species should not be purchased for a domestic aquarium.
For those with genuine large-scale facilities — a pond of several thousand litres or a large public or institutional tank — the care parameters are broad: temperature 68–82 °F, pH 6.0–8.0, soft to moderately hard water. The air-breathing organ means the fish must have access to the water surface; keep a gap between the water surface and any lid, and ensure the lid is secure, as this fish can push out of uncovered tanks. The scaleless skin is sensitive to copper-based medications and to many other chemical treatments — dose conservatively and avoid copper entirely if possible. Handle with extreme care: the serrated, locking pectoral and dorsal spines are capable of causing serious puncture injuries. Always move this fish in a solid container, never in a net. Once established in a water body, Clarias gariepinus is a notorious invasive species and must never be released into open water.
Feed large meaty foods — whole fish, prawns, earthworms, large carnivore pellets — after dark. Any tankmate small enough to be eaten will be eaten.
Conservation
The IUCN Red List assesses Clarias gariepinus as Least Concern. It is among the most abundant and widespread freshwater fish in Africa, present across nearly every major drainage of the continent, and is harvested and farmed at such scale that it is economically one of the most important freshwater food fish in Africa. Population pressures from fishing are offset by the ease of aquaculture production and the species' adaptability.
The conservation picture is complicated by the species' status as an invasive elsewhere in the world. Introduced populations established in parts of Asia (Thailand, Indonesia, the Philippines, Malaysia), the Middle East, and southern Europe have had documented negative impacts on native freshwater fauna through predation and competition. In Florida, introductions of congeners (notably the introduced Asian walking catfish Clarias batrachus) have long been considered a management problem. The native African range is considered stable; it is as an invasive that Clarias gariepinus poses an ecological risk, and release into open water must never occur.