Taxonomy & naming
Acantopsis thiemmedhi was described by the Thai ichthyologist Prachya Sontirat in 1999, within the family Cobitidae, the spined and pond loaches. For many years the genus Acantopsis was treated as containing only one or two widely-distributed "horseface loach" species, with much of the material from Thailand, Myanmar, Cambodia, Laos and Vietnam lumped under names like Acantopsis dialuzona or A. choirorhynchos. A 2017 revision of the genus (published in Zootaxa) combined molecular and morphological analysis and confirmed A. thiemmedhi as one of four valid species, distinguishing it from its relatives on details of fin length and body proportions.
The species epithet honours Professor Jindah Thiemmedh, a Thai zoologist; the common name "Jinda's Horsefaced Loach" preserves an alternate transliteration of the same name. As with other recently-resolved Acantopsis species, older hobby and literature records that simply say "Acantopsis sp." or attribute Thai horseface loaches to A. dialuzona may in fact refer to this species — a reminder that the genus was a taxonomic tangle until quite recently. The Catalog of Fishes is the standing authority for the current combination, Acantopsis thiemmedhi.
Morphology
This is a true loach in the fullest sense: an elongate, cylindrical Cobitidae with a long, pointed, distinctly upturned snout — the "horseface" that gives the genus its common name — and small eyes set high on the head, an adaptation for a fish that spends much of its life buried in sand looking upward. Like other Cobitidae it carries an erectile suborbital spine, a small defensive blade folded into a groove beneath the eye that can be flicked out when the fish is handled or threatened; keepers should scoop rather than net it to avoid the spine catching in the mesh.
FishBase records a maximum size of about 4.5 in standard length, making it a mid-sized member of the family — noticeably larger than dwarf loaches but far short of the big botiids. The body carries small, deeply embedded scales rather than the fully naked skin of some cobitids, but it is still thin-skinned by ordinary fish standards, a point that matters for medication. The 2017 genus revision found that males have longer pectoral fins than females, a modest but useful sexually dimorphic trait within Acantopsis.
Habitat
Acantopsis thiemmedhi is native to Thailand, where FishBase describes it living in mountain streams and the upper reaches of rivers over sandy bottoms, in clear, running water. This is a tropical, not temperate, species — it inhabits warm foothill and highland streams rather than the cool lowland or seasonal waters that some of its Eurasian Cobitidae relatives (Cobitis, Sabanejewia, the dojo Misgurnus) tolerate.
The species has a documented high oxygen requirement and low tolerance for organic pollution, consistent with a fast-flowing, well-aerated stream habitat. A soft, sandy substrate is essential to its natural burrowing behaviour — it is a sand-sifter that needs loose, fine sediment to bury into and forage through, and a stream bed of gravel, mud or a hard bottom does not suit it.
Feeding
Acantopsis thiemmedhi is a benthic omnivore and a committed sand-sifter: it forages by burrowing through soft sand, taking small invertebrates and detritus sifted out along the way, in the manner typical of the genus. Wild individuals likely take worms, insect larvae and small crustaceans encountered in the substrate, supplemented by organic detritus.
In the aquarium it should be offered sinking foods that reach the bottom quickly — sinking pellets and wafers, and frozen or live foods such as bloodworm and small crustaceans — since it feeds at substrate level and rarely competes well for food in the water column. A soft sand bed is not just cosmetic here: without one to sift through, this species cannot express its natural foraging behaviour and can struggle to find food at all.
Mating
Documented information on courtship in Acantopsis thiemmedhi is sparse; no aquarium spawning has been reliably reported. The 2017 genus revision noted that males have longer pectoral fins than females and that fin-length characteristics appear linked to breeding condition in at least some Acantopsis species, suggesting a seasonal reproductive cycle tied to fin development, but the details of courtship behaviour itself have not been described for this species.
As with most horseface and other tropical Cobitidae, spawning in the wild is presumed to follow the seasonal rains typical of Southeast Asian monsoon streams, but this has not been directly observed and documented for A. thiemmedhi specifically. Data here is genuinely sparse, and any account of courtship behaviour beyond the fin-length dimorphism would be speculation.
Breeding
Acantopsis thiemmedhi is presumed to be an egg-scattering species with no parental care, in keeping with the rest of the family Cobitidae, but no confirmed tank breeding has been documented for it. Unlike the temperate spined loaches (Cobitis, Sabanejewia) and the dojo or weather loach (Misgurnus anguillicaudatus), which have been pond- or tank-spawned by hobbyists and breeders taking advantage of a coldwater seasonal cycle, the tropical horseface loaches of Acantopsis have generally not been bred in captivity.
The honest picture for this species is simple: it is essentially unknown as a captive-bred aquarium fish. Any specimens in the trade should be assumed wild-collected from Thai mountain streams rather than farm- or hobby-bred, and a keeper should not expect to replicate spawning without recreating the seasonal flow, temperature and substrate cues of its native highland habitat — conditions well beyond a standard home tank.
In the aquarium
This is a specialist's fish, not a generalist community loach. The single most important requirement is a soft, fine sand substrate deep enough for the fish to bury into — without it, A. thiemmedhi cannot express its natural sifting and burrowing behaviour and will be visibly stressed. It also needs strong water movement and high dissolved oxygen, reflecting its origin in clear, fast mountain streams; stagnant or poorly oxygenated water is poorly tolerated, and FishBase specifically notes intolerance of organic pollution, so stable, clean water quality is essential.
Like other Cobitidae it is thin-skinned and sensitive to copper-based treatments and full-strength doses of many medications, so any treatment should start at reduced strength. Being a burrowing, largely nocturnal or crepuscular sand-dweller, it is easy to overlook or believe absent from a tank — feeding after lights-out and watching for the telltale sand "volcano" it kicks up when active help confirm it is doing well. Size the tank to its roughly 4.5 in adult length and provide a spacious sand-floored area free of sharp gravel that could injure its sensitive underside.
Conservation
Acantopsis thiemmedhi is listed as Data Deficient on the IUCN Red List, reflecting insufficient field survey data on its distribution, population size and trends within Thailand. This is a common status for narrow-range mountain-stream Cobitidae that have only recently been resolved as distinct species and have not received dedicated conservation assessment.
As a mountain-stream specialist dependent on clean, well-oxygenated, sand-bottomed water, it is inherently vulnerable to the pressures that affect Southeast Asian highland streams generally — sedimentation, deforestation and water pollution — even though no specific population decline has been documented. Given its Data Deficient status and its dependence on high water quality, any specimens reaching the aquarium trade should be assumed wild-collected, underscoring the importance of maintaining pristine water conditions for animals that had no cushion of captive-bred supply to begin with.