Taxonomy & naming
Clarias longior was described by the Belgian-British ichthyologist George Albert Boulenger in 1907. It belongs to the family Clariidae, the airbreathing or "walking" catfishes, and to the genus Clarias, a large African and Asian genus of naked-skinned, labyrinth-organ-bearing catfishes. The species is recognised as valid in FishBase, GBIF and ITIS records.
The epithet longior is Latin for "longer", referring to the species' relatively elongate, anguilliform (eel-like) body compared to other members of the genus — a build shared broadly across Clarias but especially pronounced in this species. Data on this species specifically is sparse; much of what is known about its biology is inferred from close congeners such as C. gariepinus, and should be read with that caveat.
Morphology
As in every Clarias, the body is elongate and cylindrical, tapering toward a long-based dorsal fin and a long-based anal fin that both run much of the length of the body, giving the fish its characteristic eel-like silhouette — accentuated in this species by the "longer" body form implied by its name. The head is broad and flattened, the mouth wide with four pairs of barbels, and the skin is completely scaleless, smooth and mucus-covered.
A precise adult size for Clarias longior is not established in the sources consulted here (data sparse). Aquarists should not treat this as reassuring — the genus is a well-documented size trap: closely related species sold as small juveniles (C. gariepinus exceeds 67 in, C. batrachus can pass 23.5 in) grow rapidly into large, heavy pond- or public-aquarium fish, and C. longior should be assumed capable of substantial size unless proven otherwise. Like other clariids it has a paired suprabranchial (labyrinth) organ above the gills that lets it breathe atmospheric air directly, and it can survive out of water for extended periods and even move short distances overland between pools.
Habitat
Species-specific habitat data for Clarias longior was not found in the sources consulted; the genus as a whole is characteristic of African fresh waters, from quiet lakes, ponds, floodplain pools and swamps to flowing rivers, and clariids are known for tolerating turbid, oxygen-poor water that would stress most other fish, an ability that follows directly from their air-breathing organ.
By genus-level proxy (Clarias gariepinus, a close relative used here only as an indicative comparison, not a confirmed match for this species), water temperatures in the group span roughly 46–95 °F with optimal growth around 82–86 °F, and pH in the range of about 6.5–8.0. Treat these as general genus context rather than confirmed figures for C. longior specifically.
Feeding
Clarias are opportunistic omnivores and, as they grow, increasingly capable predators — nocturnal hunters that will eat any fish or invertebrate small enough to swallow, alongside insects, crustaceans, detritus and plant matter. Species-specific dietary data for C. longior was not found, but this genus-level pattern should be assumed.
In captivity, Clarias readily accept pellets, meaty frozen foods and whole prey items. Because of their predatory size and appetite, tankmates must be too large for the catfish to swallow — a Clarias will not distinguish between "dither fish" and a meal once it has grown past its juvenile stage.
Mating
No species-specific courtship or spawning behaviour for Clarias longior was found in the sources consulted. Across the genus, Clarias are large, fast-growing fish that reach maturity and spawning size well beyond what a typical aquarium can accommodate, and the group is propagated almost exclusively through artificial, hormone-induced spawning at commercial hatcheries rather than through natural pairing in captivity.
Breeding
This is a large, commercially significant genus and Clarias longior should be treated the same way as its relatives: it is farm- or hormone-bred at scale for aquaculture and is essentially not bred in the home aquarium. Commercial production of Clarias typically uses hormone injection (hypophysation) to induce spawning in ponds or tanks, followed by artificial fertilisation and larval rearing — a process entirely outside the scope of hobbyist fishkeeping.
Genus-level information (from PlanetCatfish, describing Clarias breeding behaviour generally rather than this species specifically) notes that Clarias can be cavity nesters in the wild, digging a hollow roughly 12 in across in gravel or substrate, with both sexes participating and eggs laid at water temperatures around 77 °F. Even so, the fish's eventual size makes deliberate home breeding impractical, and no home-aquarium spawning reports for C. longior were found.
In the aquarium
Clarias longior is not a suitable long-term aquarium fish for the vast majority of keepers. It belongs to a genus notorious for the size trap: an innocuous-looking juvenile a few centimetres long can grow into a large, thick-bodied adult that no ordinary home tank can house, and this species' "longer" build only adds to the footprint. Anyone offered one should plan for a large public-aquarium-scale system or a pond, not a home tank, and should never release an unwanted specimen into local waterways — Clarias species are notorious invasives outside their native range.
Because it is completely scaleless, this catfish is medication-sensitive: copper-based treatments and many standard medications should be dosed conservatively, often at reduced strength, as with other naked-skinned catfish. It carries stiff, serrated pectoral spines typical of the genus, which can lock erect, tangle in a net and jab the handler — move it in a container rather than netting it. As an air-breather it needs unobstructed access to the surface to gulp atmospheric oxygen, and it is a nocturnal predator that will eat any tankmate small enough to swallow, so companions must be selected accordingly and be too large to be prey.
Conservation
The IUCN Red List assesses Clarias longior as Least Concern. Detailed rationale and population trend were not available in the sources consulted, so the assessment should be read as a broad, not-currently-threatened status rather than one accompanied by a fully documented population narrative.
As with many members of this large, adaptable, and in places heavily farmed genus, threats and status can vary considerably by locality even where the overall Red List category is favourable. Data on this species specifically remains sparse; there is little to report beyond the LC assessment itself.