Taxonomy & naming
Clarias insolitus was described by Heok Hee Ng in 2003, based on a holotype (5 in SL) and seven paratypes (2–5.5 in SL) collected in 1991 from the upper Barito River system in Kalimantan Tengah, Indonesian Borneo. It belongs to the family Clariidae, the airbreathing or walking catfishes, within the genus Clarias, which spans Africa and Asia and includes species ranging from small stream-dwellers to large farmed food fish.
The species epithet insolitus is Latin for "unusual" or "unaccustomed", a fitting name given how the original description sets this species apart from its Southeast Asian congeners: a distinctively long, thin anterior fontanel on the skull and hypertrophied sensory canal pores that are visible to the naked eye, along with a uniform violet-gray body lacking the white spotting seen in some relatives. The Catalog of Fishes (Eschmeyer, CAS) recognises Clarias insolitus as a valid species; no synonymy or generic reassignment is noted.
Morphology
Clarias insolitus is a small walking catfish, with the holotype measuring 5 in SL and paratypes ranging 2–5.5 in SL; FishBase gives a maximum size of 5.5 in SL. Like all Clarias it has an elongated, cylindrical body, a flattened head, four pairs of barbels around the mouth, and a long-based dorsal fin running most of the length of the back paired with a similarly long anal fin — the hallmark silhouette of the walking catfishes.
The species is diagnosed by a long, thin anterior fontanel on the skull and sensory canal pores on the head that are hypertrophied — large enough to see without magnification, an unusual feature among its Southeast Asian relatives. The body is a uniform violet-gray, without the white spots present in some congeners, and the pectoral spine carries prominent serrations along its anterior edge. Meristic counts from the original description include 67–76 dorsal soft rays, 53–63 anal soft rays and 61–63 vertebrae, with no dorsal spine. As in all Clarias, the skin is entirely scaleless.
Habitat
This species is endemic to the upper Barito River drainage in Kalimantan Tengah, Central Kalimantan, on the island of Borneo, Indonesia — known only from small freshwater streams within that system. Its distribution appears to be narrow and confined to this one river drainage, consistent with the pattern of localised endemism seen across Borneo's freshwater fish fauna.
Detailed data on the specific microhabitat, water chemistry, and seasonal conditions of these streams was not available in the sources consulted here; the cached record does not report specific temperature or pH figures for the type locality. As a Bornean lowland-to-upland stream fish, it likely experiences warm tropical conditions typical of the region, but that should not be treated as measured data for this species specifically.
Feeding
No specific dietary study of Clarias insolitus was found in the sources consulted. Clariid catfishes in general are opportunistic nocturnal predators and scavengers, taking insects, small crustaceans, other invertebrates and occasionally small fish from the stream bed, and there is no reason from the available data to expect this small-bodied Bornean species to differ substantially from that pattern. Given the genus's reputation, tankmates should always be too large to be swallowed — though for this species that consideration is largely academic, since it is not established in the aquarium trade.
Mating
No observations of courtship or spawning behaviour in Clarias insolitus were found in the consulted sources. The species has essentially no presence in the aquarium hobby and appears to be known only from its original type series and subsequent taxonomic treatments, so there is no hobbyist or scientific account of its mating behaviour to draw on here. Data sparse.
Breeding
There is no record of Clarias insolitus being bred in captivity, hobbyist or commercial. Larger and more widely farmed Clarias species (such as C. gariepinus and C. batrachus) are propagated at commercial scale using hormone-induced spawning, but this small, narrowly endemic Bornean species has no such trade importance and is not known to be kept, let alone bred, in home aquaria. Any breeding-mode description would be speculation; none is offered here.
In the aquarium
Clarias insolitus is not an aquarium fish in any meaningful sense — it does not appear in the ornamental trade, and PlanetCatfish and other hobbyist references treat it, at most, as a taxonomic curiosity rather than a species anyone keeps. Even so, the general cautions that apply to the genus are worth stating. Clarias are scaleless, so any Clarias in captivity needs conservative dosing of copper-based and other medications, the same caution used for loaches, puffers and eels. They carry stiff, serrated, locking pectoral spines that can snag a net and jab the handler, so any handling should use a container rather than a net. They are also obligate air-breathers that gulp atmospheric air at the surface, and the genus as a whole includes species that are notorious invasive escapees — none should ever be released into open waters. Given the total absence of husbandry data for this specific species, none of this should be read as an endorsement of keeping it; it remains, at most, a scientific-interest fish known from a single Bornean river system.
Conservation
The IUCN Red List assesses Clarias insolitus as Data Deficient, in an assessment dated 1 September 2018, reflecting a poorly known distribution and biology and limited commercial or aquarium importance. It is known only from the upper Barito River drainage in Kalimantan Tengah, Borneo, a narrow endemic range that would leave it vulnerable to localised pressures such as deforestation, mining, and water-quality degradation common across Kalimantan's river systems, though no population trend data exists to confirm or quantify any decline. Given its restricted known range and the general threats facing Bornean freshwater habitats, a fuller status assessment would be valuable.