Taxonomy & naming
Acantopsis bruinen was described in 2018 by Boyd, Nam, Phanara and Page, one of several horseface loach species split out as the genus Acantopsis was revised with modern taxonomic tools; older literature and hobby sources often lumped Mekong-basin horseface loaches under a single wide-ranging "Acantopsis dialuzona" or similar name before this kind of species-level work separated them. The genus Acantopsis sits in the family Cobitidae, the true spined loaches, alongside genera such as Cobitis, Sabanejewia, Lepidocephalichthys and the dojo loach Misgurnus.
As with any species described this recently, coverage in general aquarium references and databases is thin, and the record here should be read as provisional where it touches on distribution and biology beyond the original description. The Catalog of Fishes is the standing authority for the valid combination Acantopsis bruinen; this profile does not alter or "correct" that name.
Morphology
Acantopsis bruinen has the classic horseface loach build: an elongated, subcylindrical body tapering to a long, pointed, distinctly downturned snout, with eyes set high on the head so the fish can bury itself in sand and still watch for predators and prey. Reported maximum size is small for the family, in the range of roughly 2.5–3 in standard length, in keeping with other Mekong Acantopsis.
As a member of Cobitidae it carries the erectile suborbital spine that gives true loaches their name — a sharp, hinged spine folded into a groove beneath the eye that can be flicked out defensively, and which readily catches in fine-mesh nets. Its skin, like that of other cobitids, has small, deeply embedded scales that leave it functionally near-scaleless, a point that matters for its sensitivity to medication.
Habitat
The species is known from fast-flowing streams of the Mekong basin in Thailand and Laos, over rocky and sandy substrate. This places it among the tropical members of Acantopsis rather than the temperate spined loaches of Europe and the Caucasus — it is a warm-water stream specialist, not a coldwater fish, with a preferred range in the roughly 68–77 °F band typical of these Mekong tributaries.
In the wild it lives buried for much of the day in loose sand at the stream margins or in slacker pockets of flow, emerging to forage and moving with the current. A soft, sand-dominated substrate is central to its habitat and, by extension, to keeping it successfully — this is a species built to bury, not to sit on gravel or bare glass.
Feeding
Acantopsis bruinen is a sand-sifting benthic omnivore, the defining feeding style of the horseface loaches. It buries itself in the substrate and works through it, taking worms, insect larvae, small crustaceans, molluscs and organic detritus sifted from the sand, expelling the inert material through its gills.
In the aquarium this translates directly: it needs a soft sand bed to feed and behave naturally, and does best on sinking foods — bloodworm, blackworm, brine shrimp, sinking pellets and wafers — offered where it can find them at the bottom. A gravel or coarse substrate denies it the sifting behaviour that is core to how this fish feeds and, ultimately, to its welfare.
Mating
No sexual dimorphism has been documented for Acantopsis bruinen in the sources available, and this is not unusual for a species described only in 2018 with limited follow-up study. As with other tropical Cobitidae, mature females in related species tend to appear fuller-bodied when gravid, but no reliable external marker for this species can be stated with confidence.
Spawning behaviour in the wild has not been documented for this species specifically. Related tropical Acantopsis and other Southeast Asian Cobitidae are presumed, by analogy with the family, to scatter eggs in open water with no pair bond or courtship display beyond release of eggs and milt — but this should be read as an inference from the family, not a direct observation of A. bruinen.
Breeding
Acantopsis bruinen has not been bred in the home aquarium as far as the available sources record, and this fits the wider pattern for the genus. Tropical Cobitidae such as the horseface loaches (Acantopsis) and Lepidocephalichthys generally have not been spawned by hobbyists, in contrast to some temperate spined loaches — Cobitis, Sabanejewia, and especially the dojo or weather loach Misgurnus — which have been pond- or tank-spawned in cooler conditions.
Where spawning is documented for the family at all, it follows the loach pattern of egg-scattering: adhesive eggs released among plants or fine substrate with no parental care whatsoever, typically triggered by a seasonal rise in water level and flow. No such event has been recorded for A. bruinen, and there is no farm or hormone-induction supply chain reported for this species either — it simply is not a fish that gets bred, in captivity or on farms.
In the aquarium
Acantopsis bruinen is a specialist fish, not a casual community addition, and its needs follow directly from its biology. It absolutely requires a soft, fine sand substrate deep enough to bury in — anything coarser prevents its natural burrowing and sifting behaviour and can injure its barbels and skin. Being near-scaleless like all Cobitidae, it is sensitive to copper-based medications and full-strength treatments generally, so half-doses and gentle products are the safer approach if disease treatment becomes necessary.
As a fast-water stream fish it appreciates good current and strong oxygenation, and a soft, acidic-to-neutral, warm setup in roughly the 68–77 °F range reflects its native Mekong streams. Given how recently it was described and how little is written about it in the hobby, keepers should treat husbandry information as provisional and lean on the general Acantopsis/horseface-loach template — sand, current, dim lighting, and a calm tankmate roster — until more is known specifically about this species.
Conservation
Acantopsis bruinen has not been formally assessed on the IUCN Red List. Given its description in 2018 and apparently narrow known range within Mekong tributaries of Thailand and Laos, a Not Evaluated status should be read as a gap in assessment coverage rather than any signal of security — recently described stream endemics in the Mekong basin are frequently narrow-range and can be vulnerable to the river's well-documented pressures from damming, sand mining, and water-quality decline.
No dedicated trade or export data for this species were found in the sources consulted; it does not appear to be a significant aquarium-trade fish at present. As with many recently split Mekong stream fishes, the most useful conservation step is simply more field survey work to establish its actual range and status.