Taxonomy & naming
The species was described by Datta & Barman in 1984, originally as Noemacheilus arunachalensis, based on specimens from the Namdapha River in Tirap district, Arunachal Pradesh — a placement that reflected the loose, catch-all use of Noemacheilus for stone loaches at the time. Subsequent taxonomic review moved it first into Lepidocephalus and then into Lepidocephalichthys, the genus of spiny-eyed or spirit loaches within family Cobitidae, where it sits today alongside close relatives such as L. guntea, L. berdmorei and L. thermalis.
A published revision of the genus notes that the Indian Lepidocephalichthys — including L. arunachalensis, L. manipurensis and L. coromandelensis — still need further comparative work to settle their limits and relationships, so the group is best treated as taxonomically unsettled rather than fully resolved. The Catalog of Fishes is the authority for the currently valid combination, Lepidocephalichthys arunachalensis (Datta & Barman, 1984); the parenthetical authority signals the change of genus since the original description.
Morphology
Lepidocephalichthys arunachalensis is a small, slender-bodied true loach in the sense that matters most for identification: it carries the erectile, forked suborbital spine tucked beneath the eye that defines family Cobitidae, a defensive structure it can flick out when handled or threatened. Like its relatives it is effectively naked-skinned, its scales tiny and deeply embedded, which makes it — and every other Cobitidae species — unusually sensitive to copper and to full-strength aquarium medications.
Published description notes place the dorsal-fin origin behind the origin of the pelvic fins, and describe a rounded to truncated caudal fin and a flank pattern of roughly 12–14 dark spots along the body, a pattern that helps separate it from the similar L. guntea and L. berdmorei. Exact maximum size has not been documented in the literature available; based on the small-bodied genus as a whole it is very unlikely to exceed the low teens of centimetres in total length.
Habitat
This is a tropical foothill species, not a coldwater one — a distinction worth making explicitly, because several of its Cobitidae relatives (the European spined loaches Cobitis and Sabanejewia, and the dojo or weather loach Misgurnus) are temperate fish suited to unheated tanks or ponds, while L. arunachalensis lives in the warm rivers of the eastern Himalayan foothills. It is endemic to Arunachal Pradesh, known from the Namdapha River and its Namdapha Wildlife Sanctuary type locality in Tirap district, with further records from the East Siang, Lower Dibang Valley and Siyom drainages.
Its habitat is described as foothill streams and rivers running over mixed cobble, sand and silt substrates — fast-flowing, well-oxygenated water typical of the eastern Himalayan drainage system before it broadens into the Brahmaputra plains. Precise water-chemistry data for the species itself has not been published; related Lepidocephalichthys such as L. thermalis are documented from cool, clear mountain streams around 72–75 °F and near-neutral pH, which gives a reasonable working picture for the genus in this kind of habitat.
Feeding
As in other Cobitidae, Lepidocephalichthys arunachalensis is almost certainly a sand-sifting benthic omnivore, working the fine substrate of its home streams for worms, insect larvae, small crustaceans, molluscs and detritus — the same foraging strategy documented across the genus and family. No species-specific dietary study is available, but the family's feeding mode is consistent enough that it can be stated with confidence.
Were it kept, it would need a soft sand bed to sift through in order to feed and forage naturally, exactly as recommended for its better-known relatives such as L. guntea and L. thermalis; a hard or coarse substrate would deny it its normal way of finding food.
Mating
No spawning behaviour has been documented for this species in the wild or in captivity, and it is not established in the aquarium hobby, so there are no keeper observations to draw on either. Data is genuinely sparse here rather than simply unrecorded in the sources consulted.
Breeding
Breeding has not been documented for Lepidocephalichthys arunachalensis. Going by the pattern seen across the tropical members of Cobitidae — including its own genus and the horseface loach Acantopsis — the species is expected to be an egg-scatterer with no parental care, releasing eggs among vegetation or into the current with no guarding behaviour of any kind. That pattern contrasts with the temperate Cobitidae (Cobitis, Sabanejewia, and the dojo Misgurnus), several of which have been pond- or tank-spawned in cooler water; the tropical genera, this species included, have generally not been bred by hobbyists. There is no record of this species being spawned in captivity.
In the aquarium
Lepidocephalichthys arunachalensis is not established in the aquarium trade — it does not appear in the hobbyist literature as an available species, and this profile is built from taxonomic and conservation sources rather than any keeper experience. Should it ever appear, the sensible starting point is the care template that works for its better-documented relatives: warm, clean, well-oxygenated water, a fine soft sand substrate for natural sifting and feeding, and gentle to moderate flow reflecting its foothill-stream origin.
As with every Cobitidae species, its near-scaleless skin means it would be sensitive to copper-based treatments and to full-strength doses of many standard medications, so any future keeper should plan on half-doses and gentle products. Given how narrow and pressured its known range already is, any aquarium interest in this species should rest on captive-bred stock rather than further wild collection.
Conservation
Lepidocephalichthys arunachalensis is assessed as Endangered (EN) on the IUCN Red List. It is endemic to a small number of river drainages in Arunachal Pradesh — the Namdapha, East Siang, Lower Dibang Valley and Siyom systems — which leaves it inherently vulnerable to any single pressure across that limited range, from habitat degradation to hydrological change in the eastern Himalayan foothills.
The species is not part of the aquarium trade, so ornamental collection is not a documented threat; the pressures implied by its Endangered status are more likely tied to its restricted, foothill-stream habitat and the general vulnerability of narrow-range endemics in a fast-developing region. Precise threat data specific to this species was not found in the sources consulted, and this profile does not speculate beyond the assessed status itself.