Taxonomy & naming
Clarias anguillaris was first described by Carl Linnaeus in 1758, making it one of the earliest-named African catfishes in the formal literature; the original description appeared in the tenth edition of Systema Naturae. It belongs to the family Clariidae, the walking catfishes, within the order Siluriformes. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) treats Clarias anguillaris as the valid name and recognises Clarias as the nominal genus.
Historically the species was sometimes listed under older synonyms or confused with the closely related African sharptooth catfish Clarias gariepinus, which overlaps it in much of West Africa and is far more widely studied in aquaculture. The two species can be separated reliably by gill raker count: C. anguillaris has 14–40 gill rakers on the first arch, while C. gariepinus carries 20–100. The species epithet anguillaris is Latin for 'eel-like', describing the elongated, sinuous body and the smooth, scaleless skin that give the fish a superficially eel-like silhouette.
Morphology
The body is long and laterally compressed toward the tail, giving the eel-like outline the epithet describes. The head is broad and strongly depressed, bearing four pairs of unbranched barbels: one pair each of maxillary, nasal, inner mandibular and outer mandibular barbels. There is no adipose fin; the dorsal and anal fins are long-based and run to the tail. Like other clariids, C. anguillaris carries stiff, serrated, locking spines at the leading edge of the dorsal and pectoral fins — these spines can be locked erect, they tangle badly in nets, and they can jab the keeper painfully. Always move this fish in a container, never a net.
The skin is entirely scaleless and smooth, giving the fish a wet, mucus-coated surface. Scaleless skin means reduced protection from copper-based and several other chemical treatments — dose conservatively, at half-strength or less, as with loaches and eels. Adults are typically a uniform grey-brown to olive-brown above and paler beneath, with no bold markings. Maximum recorded length is 39.5 in TL; average West African individuals run about 25.5 in TL, with weight up to 7 kg.
The most striking internal feature is the suprabranchial accessory breathing organ, a spongy, vascularised chamber above the gill arches that functions like a simple lung. In oxygen-poor water the fish rises to gulp air at the surface; access to the water surface is not optional — a clariid deprived of atmospheric air will drown.
Habitat
Clarias anguillaris inhabits a broad swathe of West and North Africa, from the Nile (lower and middle reaches) through the Lake Chad system (Logone and Shari rivers) to the Niger and Benoue, and along the Atlantic coastal rivers of Ghana, Togo, Benin, Côte d'Ivoire, Gambia and Senegal, including the Volta drainage. It is a freshwater demersal fish, living over soft or muddy substrates in rivers, lakes, floodplains and seasonal pools.
A key behavioural trait is aestivation: during the dry season, when shallow pools shrink and water bodies contract, C. anguillaris buries itself in moist mud and becomes dormant, surviving until seasonal rains return and reconnect the water system. This makes it a potamodromous species — it moves within river systems with flood pulses and receding water levels rather than migrating to the sea. Spawning is timed to the rainy season, when inundated floodplain areas provide feeding and breeding opportunities.
Water conditions across its range are variable — warm, neutral to mildly alkaline West African rivers, with temperatures similar to the sympatric C. gariepinus (46–95 °F thermal tolerance, optimum around 82–86 °F; pH 6.5–8.0). This is not a soft-acidic blackwater fish.
Feeding
Clarias anguillaris is an opportunistic omnivore with a strong piscivorous tendency at large body sizes. The diet documented across its range includes fish, molluscs, crustaceans, insect larvae (especially Diptera), algae, plant material and detritus. Juveniles are more varied in their feeding, but dietary diversity narrows as the fish grows and large individuals become predominantly piscivorous — they will eat any animal prey they can engulf.
In an aquarium context this translates simply: any fish, frog or invertebrate small enough to swallow will be eaten. Tankmates must be substantially larger than the catfish's gape. Feed large meaty foods — whole or chunked fish flesh, prawns, earthworms, large sinking catfish pellets — and expect a vigorous nocturnal feeder that sweeps the bottom after lights-out. Overfeeding a fish of this size produces significant waste; filter capacity must be sized accordingly.
Mating
In the wild, spawning in Clarias anguillaris is triggered by the onset of the rainy season and associated flooding. Rising water levels, increased turbidity and dropping barometric pressure appear to act as spawning cues, and adults move onto inundated floodplain areas to breed. The species is not known to be sexually dimorphic in a way that makes reliable field sexing straightforward, though gravid females become visibly distended with eggs before spawning.
In commercial aquaculture, which is where virtually all knowledge of this species' reproduction derives, both sexes require hormonal induction to spawn in captivity. Pituitary extract or synthetic analogues (such as LHRHa or human chorionic gonadotropin) are injected, and stripping — manual expression of eggs and milt — is common practice. Natural courtship and pair-spawning in the home aquarium essentially do not occur; the fish grows too large and requires hormone intervention to reproduce.
Breeding
Clarias anguillaris is farm- and hormone-bred at commercial scale and is not bred in the home aquarium. The fish is an economically significant food fish across West Africa, and its aquaculture is well documented: hatcheries use hormone injection to synchronise ovulation, strip the eggs and milt, fertilise artificially, and rear the larvae in controlled conditions. This is the exclusive pathway for captive reproduction.
The home aquarist keeping this species should not expect to breed it. Adults quickly exceed the space available in any domestic tank, and induced spawning requires veterinary-grade hormones and dedicated facilities. The species has no parental care behaviour in the familiar sense — it does not guard a nest or mouth-brood — but the reproductive biology of a fish this size is academic for almost all hobbyist contexts.
In the aquarium
Clarias anguillaris is not a practical home-aquarium fish. An adult reaches 39.5 in TL and weighs up to 7 kg — the scale of a large Python or public-display fish — and even a 'reasonable' captive size of 25.5 in demands a tank measured in the hundreds or thousands of litres. This is the size-trap genus of the Clariidae: juveniles are sold at 2–4 in and are sometimes passed off as novelty 'mini catfish'; the buyer ends up with a pond fish. Purchase only if permanent large-volume housing exists.
If space is genuinely available, care is straightforward. The fish is hardy across a wide thermal range (comfortable from roughly 72–86 °F) and tolerates pH 6.5–8.0. Soft, neutral West African river water is appropriate. Heavy, efficient biological filtration is non-negotiable given the fish's output at full size. Provide a tight-fitting, weighted lid: clariids climb and can cross damp surfaces; escape is common in open tanks. Because the suprabranchial organ is obligate, an air gap of a few centimetres above the water surface must always be maintained.
The skin is scaleless, so treat this fish as you would an eel or loach where medication is concerned — avoid full-dose copper treatments and standard broad-spectrum medications without dilution; half-dose or catfish-safe alternatives are advisable. The locking pectoral and dorsal spines tangle in nets and cause painful punctures; always move the fish in a large container. Do not release this species into natural waterways under any circumstances — it is a known invasive with established feral populations in regions outside its native range, and its air-breathing, mud-burrowing lifestyle makes eradication extremely difficult.
Conservation
The IUCN Red List assessed Clarias anguillaris as Least Concern in 2022. The species is widespread across West Africa and the Nile drainage, occupies a large area of occupancy, and is not currently considered at risk of significant population decline at the global scale. Its ability to aestivate in mud during droughts gives it resilience to habitat fluctuation that more sensitive species lack.
The fish is an important subsistence and commercial food fish across the Sahel and West African river basins, and large-scale aquaculture in several countries reduces some pressure on wild stocks. Nevertheless, localised pressures — habitat degradation, pollution of floodplain systems, overfishing in some basins, and the reduction of seasonal floods by dam construction — affect populations at the river or lake level even if the species as a whole remains widespread. Introduced populations have established in parts of the world outside its native range, where it poses ecological risks as a large predator in novel ecosystems.