Taxonomy & naming
Clarias anfractus was described by the ichthyologist Heok Hee Ng in 1999, part of a wave of new Bornean Clarias descriptions from that period as researchers worked through the island's walking-catfish diversity. It belongs to the family Clariidae, the airbreathing or walking catfishes, and to the genus Clarias itself, which spans dozens of species across Africa and Asia, from small stream endemics like this one to the giant, invasive C. gariepinus and C. batrachus.
The genus name Clarias derives from a Greek root referring to liveliness or vigour, an old reference to the fish's ability to survive out of water and thrash about on land. The species epithet anfractus is Latin for "bent" or "winding", though the exact character it references is not confirmed here; Clarias species descriptions from this period often name morphological details of the skull or fin rays. As with most narrow-range stream Clarias, there is no history of the species being shuffled through other genera — it was described directly into Clarias and the Catalog of Fishes maintains that placement.
Morphology
Clarias anfractus is a small member of its genus. The holotype measured 7 in and five paratypes ranged from 5.5–8 in, giving a maximum recorded size of roughly 8 in — modest set against giants like C. batrachus or C. gariepinus, which are sold as small juveniles but can reach half a metre or more. Like every Clarias, its skin is completely naked and scaleless, an elongated eel-like body tapers to a rounded tail, and the dorsal and anal fins run long along the body without joining the caudal fin.
The pectoral fins each carry a stiff, serrated spine with an irregular outline that can be locked erect — a feature shared across the genus and one that can snag a net or jab an unwary hand. The body carries scattered pale spots along its sides, a pattern noted as a useful field mark against co-occurring Clarias. As an airbreather, it has the accessory branching organ typical of the family, allowing it to gulp atmospheric oxygen and survive in poorly oxygenated pools.
Habitat
This species is endemic to Sabah, in Malaysian Borneo, known from the Segama and Kalabakan river drainages. It lives in the slow pools of forested, fast-flowing streams, on substrate of mud and soil thick with leaf litter and debris, and it shelters in burrows or holes dug into that substrate by day, emerging to forage at night.
As a small-range Bornean forest-stream endemic, it depends on intact rainforest catchments — the same leaf-litter, slow-pool habitat that supports much of the island's small blackwater and forest-stream fish fauna. Specific water chemistry has not been documented for this species in the sources available; forest streams of this type in Borneo are typically soft and acidic, but that should be treated as inference from habitat type rather than a measured value for this species.
Feeding
Detailed dietary data for Clarias anfractus has not been documented. As with other small stream Clarias, it is presumed to be a nocturnal predator of invertebrates and small aquatic animals it can find in the leaf litter and mud of its pool habitat — worms, insect larvae, crustaceans and similar prey, taken opportunistically after dark.
In the aquarium, walking catfish of this genus generally accept a wide range of meaty foods: sinking pellets, frozen bloodworm, prawn and other prepared foods. Given the uncertainty around wild diet specifics, offering a varied, protein-rich diet after lights-out is the safest approach; data is sparse enough that specifics should not be overstated.
Mating
No courtship or spawning behaviour has been documented for Clarias anfractus specifically. Across the genus, walking catfishes typically pair or aggregate at the start of the wet season, when rising water levels trigger spawning migrations and flood newly available habitat; eggs are generally scattered over submerged vegetation or substrate rather than guarded in a nest.
Given the complete absence of aquarium or field breeding accounts for this species, any account of its specific mating behaviour would be speculation. What can be said with confidence is that it has not been bred in captivity as far as documented, and its natural history in this respect remains essentially unstudied.
Breeding
Breeding of Clarias anfractus in the aquarium has not been documented. Large, well-known Clarias — C. batrachus, C. gariepinus and their farmed relatives — are propagated at commercial scale using hormone-induced spawning, a technique built around species that mature at a large size and are raised in ponds or tanks for food production; they are essentially never bred by home aquarists.
Clarias anfractus is a much smaller species and a narrow-range wild endemic rather than an aquaculture fish, so it falls outside that commercial pipeline entirely — but that also means no home-breeding method has been worked out or reported for it either. Anyone attempting to breed it would be working from first principles, informed at best by the general biology of small stream-dwelling Clarias rather than by any species-specific record.
In the aquarium
Clarias anfractus is rarely if ever seen in the aquarium trade, and specific care information is not documented in the available literature. What can be said follows from its genus and its measured size: at a recorded maximum of about 8 in, it stays much smaller than trade staples like C. batrachus, but any Clarias needs a securely covered tank, since walking catfishes are strong, determined escape artists that can survive out of water for extended periods using their air-breathing organ.
Like all Clarias its skin is completely scaleless, so it should be treated as medication-sensitive — dose copper-based treatments and many standard medications conservatively, as with loaches, puffers and other naked-skinned catfish. Its pectoral spines lock and can snag a net or jab the keeper, so it is safer to move in a submerged container than to net directly. As a nocturnal burrower from leaf-littered forest streams, it should be given a soft substrate, hiding places, and cover from light, with feeding offered after dark. Given how little is documented about this species, and the invasive track record of larger Clarias elsewhere, this is not a fish to acquire casually or release if unwanted.
Conservation
The IUCN Red List assesses Clarias anfractus as Least Concern. It is a narrow-range Bornean endemic, restricted to the Segama and Kalabakan drainages of Sabah, but is not currently considered threatened.
As with many small-range forest-stream fishes, its long-term outlook is tied to the health of its specific catchments — logging, land conversion and sedimentation in Sabah's forested river systems are the pressures most likely to matter over time, even though the species is not currently flagged as at risk. It is not known to be part of any established aquarium trade, so collection pressure is presumed minimal.