Taxonomy & naming
Clarias dayi was described by the Indian ichthyologist Sunder Lal Hora in 1936. It belongs to the family Clariidae, the airbreathing or walking catfishes, within the large genus Clarias, which spans Africa and Asia and includes both small stream species and the pond-scale giants the genus is best known for. The species was for a time treated as a subspecies, Clarias dussumieri dayi, before being accepted as a distinct species; the Catalog of Fishes (Eschmeyer, CAS) currently recognises Clarias dayi as valid.
The epithet dayi honours Francis Day (1829–1889), a British surgeon and Inspector-General of Fisheries in India whose 19th-century surveys of Indian freshwater fishes remain a foundational reference for the region's ichthyofauna. Clarias dayi is endemic to peninsular India and is one of several small, poorly known Clarias restricted to the hill streams of the Western Ghats.
Morphology
Like other members of its genus, Clarias dayi has the classic walking-catfish build: an elongated, cylindrical body, a flattened, bony head, a long-based dorsal fin running most of the length of the back, and four pairs of barbels around the mouth used to feel out food in dim or turbid water. The skin is scaleless and covered in a thick mucus layer typical of the family.
Reported maximum size is around 7 in total length (FishBase) — a genuinely small species for the genus Clarias, which elsewhere includes fish that reach half a metre or more. As in all Clariidae, the pectoral fins carry a stiff, serrated spine that can lock erect; this is capable of jabbing an unwary hand and can snag in an aquarium net.
Habitat
Clarias dayi is confined to fast-flowing hill streams in tropical peninsular India, with records from the Wynaad Hills of Kerala and further reports from Ombatta and the Mudumalai area of Tamil Nadu. These are cool, clear, well-oxygenated streams draining the Western Ghats, a globally recognised biodiversity hotspot, typically running over rock and gravel substrates with riffles and pools.
As an air-breather, the species is equipped with an accessory respiratory organ that lets it survive in water with low dissolved oxygen, and it can move overland between pools during the wet season — the "walking" habit shared across the genus. Specific published data on this species' temperature and pH tolerances are sparse; as a Western Ghats hill-stream fish it is presumed to favour cool, well-aerated, running water rather than warm, still conditions, but hobbyist or field water-chemistry measurements for Clarias dayi specifically have not been located.
Feeding
Detailed dietary studies of Clarias dayi are not available. Clariid catfishes in general are opportunistic omnivores to predators, using their barbels to locate aquatic invertebrates, small crustaceans and other prey by feel along the stream bed, especially after dark. Given its modest adult size, Clarias dayi is best treated as a benthic invertebrate feeder rather than a fish-eating predator on the scale of its larger relatives.
In the near-total absence of aquarium accounts, feeding recommendations must be extrapolated from the genus: sinking meaty foods, invertebrates and prepared pellet diets offered after dark would be expected to suit it, but this has not been confirmed for the species itself.
Mating
No courtship or spawning behaviour has been documented for Clarias dayi. Other small stream-dwelling Clarias are generally believed to pair up and scatter adhesive eggs over gravel or amongst vegetation during the monsoon rains, when rising, well-oxygenated flows trigger spawning, but this pattern has not been confirmed for Clarias dayi itself and should not be assumed as fact.
Breeding
There is no record of Clarias dayi being bred in captivity, home aquaria or commercial hatcheries. The genus Clarias contains species that are farmed and hormone-spawned at industrial scale (such as the African sharptooth catfish and the Asian walking catfish), but Clarias dayi is a narrow-range, poorly studied Western Ghats endemic with no aquaculture or aquarium-trade profile, and nothing has been published on inducing or observing its reproduction. Prospective keepers should treat this species as effectively unbred in captivity and not expect to reproduce it at home.
In the aquarium
Clarias dayi is not established in the aquarium trade and aquarium-specific care information does not exist for this species. Even so, its biology sets clear expectations. At an adult size of roughly 7 in it is far smaller than the well-known giant walking catfishes, but it is still an active, air-breathing benthic feeder that will need to reach the surface periodically to gulp air, so any enclosure must leave an air gap and a secure, gap-free lid — Clariidae are notorious escape artists that can travel overland.
Like all catfish it is scaleless, so it should be treated as medication-sensitive: dose copper-based treatments and other medicines conservatively, following half-strength guidance used for other naked-skinned catfish. Its pectoral spines lock and can snag a net or jab a hand, so it is safer to move in a container than to net directly. Strong water flow, cover (rock and driftwood), and clean, well-oxygenated water reflecting its hill-stream origin would be the sensible baseline, though none of this has been tested in the hobby. Given how little is documented, this is a species for a specialist prepared to work largely from first principles rather than an established care sheet — and, as with other Clarias, it should never be released into local waterways.
Conservation
The IUCN Red List does not currently carry a dedicated assessment for Clarias dayi; FishBase lists its status as Data Deficient as of 2020. As a narrow-range endemic restricted to a handful of hill-stream localities in the Western Ghats of Kerala and Tamil Nadu, it is potentially vulnerable to the pressures affecting that biodiversity hotspot — stream damming, water abstraction, siltation from land-use change and general habitat degradation — but without population data or a formal assessment, its true conservation status is unresolved.
The absence of an aquarium trade profile means collection pressure is unlikely to be a significant threat; habitat integrity in its native Western Ghats streams is the more relevant conservation concern for this species.