Taxonomy & naming
Acantopsis octoactinotos was described by the American ichthyologist Darrell J. Siebert in 1991 (Copeia 1991(4): 910–915), as part of a revision of the horseface loaches that split the once catch-all genus Acantopsis into several distinct species. The genus remains Acantopsis, and the Catalog of Fishes — the standing authority for valid fish names — accepts A. octoactinotos as a valid species within it.
The genus sits in the family Cobitidae, the true or spined loaches, alongside the temperate Cobitis and Sabanejewia and the tropical Lepidocephalichthys. For decades hobbyists and older literature lumped most horseface loaches together under a single wide-ranging "Acantopsis dialuzona" or "A. choirorhynchos"; Siebert's 1991 revision showed that several distinct, geographically separate species exist across Southeast Asia, of which this is one, distinguished from its relatives partly by fin-ray counts (reflected in the specific epithet) and by the shape of its snout.
Morphology
This is a true loach in every sense: an elongated, laterally compressed, sand-coloured fish carrying the erectile suborbital spine that gives the family Cobitidae its common name of "spined loaches." The spine sits folded in a groove beneath the eye and can be flicked out defensively — worth remembering when netting the fish. Like other cobitids its scales are tiny and deeply embedded, leaving the skin close to naked and, as in most scaleless loaches, sensitive to medication.
The defining feature of the genus is the long, tapering, almost tubular snout, angled slightly downward and ending in a small underslung mouth flanked by barbels — an adaptation for probing and burrowing through sand. A. octoactinotos is separated from its close relative A. choirorhynchos chiefly by a straighter, less strongly downturned snout profile and by differences in fin-ray counts. It reaches a modest maximum size of around 4.5 in, with females typically growing larger and heavier-bodied than males.
Habitat
The species is known from Borneo, with its type locality in a tributary of the Kinabatangan River near Deramakot in Sabah, Malaysia, and it is recorded more broadly from Indonesia and Malaysia. This places it firmly among the tropical, Southeast-Asian members of Cobitidae, in contrast to the coldwater spined loaches (Cobitis, Sabanejewia) and the weather loach (Misgurnus) of temperate Eurasia — A. octoactinotos is a warm-water fish through and through.
It lives over clean sandy or fine-gravel beds in flowing tropical streams and rivers, where it spends much of its time buried with only its eyes and the tip of its snout exposed, sifting the substrate for food. A soft, silty-free sand bottom and reasonably clean, well-oxygenated flowing water are defining features of its natural habitat.
Feeding
Acantopsis octoactinotos is a sand-sifting benthic omnivore. In the wild it buries itself in soft substrate and works through the sand grain by grain, taking worms, insect larvae, small crustaceans, molluscs and organic detritus that it filters out through its gills as it feeds — the classic horseface loach feeding style. It relies on a fine, soft substrate to forage naturally; a hard or gravel bottom denies it this behaviour entirely.
In the aquarium it does best on sinking foods that reach the substrate — frozen bloodworm and brine shrimp are reported to be readily accepted — along with sinking pellets and wafers. Because it feeds mostly out of sight, buried in sand, keepers should make sure enough food reaches the bottom for it, rather than assuming surface feeders have left leftovers behind.
Mating
Detailed accounts of courtship in this species are not documented in the available literature; sexual dimorphism is limited to females growing larger with a fuller, deeper abdomen than males, which is the main cue keepers use to sex mature individuals. As with most tropical Cobitidae, there is no record of the seasonal or environmental cues that trigger spawning being worked out from aquarium observation.
Given how little is documented, keepers should treat any claim of predictable pairing or spawning behaviour in this species with caution — the honest state of knowledge is that its reproductive biology in captivity remains essentially unrecorded.
Breeding
Breeding is not known to have been achieved in the home aquarium for Acantopsis octoactinotos. Cobitidae as a family are egg-scatterers with no parental care, and several temperate members of the family — Cobitis, Sabanejewia, and especially the dojo or weather loach Misgurnus — have been pond- or tank-spawned by hobbyists. The tropical horseface loaches, including this species and its relatives, have not: no reliable aquarium spawning has been reported.
As with most members of this genus, the fish sold in the trade are wild-collected rather than captive-bred. Keepers should acquire A. octoactinotos to enjoy as a characterful sand-sifter, not with any expectation of breeding it at home.
In the aquarium
The single most important element of a setup for this species is substrate: it needs a deep bed of soft, rounded sand, not gravel, both to express its natural burrowing and sifting behaviour and to avoid abrading its underslung mouth and barbels. Warm water in the tropical range and a soft, near-neutral pH suit it best, matching its Bornean stream origins; it should not be kept as a coldwater fish.
Being near-scaleless, like other true loaches it is sensitive to copper-based medications and to full-strength doses of many treatments — half-doses and gentler products are the safer approach if disease treatment becomes necessary. Loaches.com notes it can be more aggressive than some related Acantopsis species, so it is worth watching how it settles with tankmates and with its own kind. At a modest maximum length of around 4.5 in it does not need an enormous tank, but it does need the right floor: sand, sand, and more sand.
Conservation
Acantopsis octoactinotos is assessed by the IUCN Red List as Vulnerable (VU), with the assessment dated 2019. This reflects its restricted known range on Borneo, where it is tied to a specific type of clean, sandy tropical stream habitat — the kind of specialist niche that is vulnerable to siltation, deforestation, and river degradation across Sabah and the wider island.
As a specialist stream fish rather than a species with broad ecological tolerance, its conservation outlook depends on the health of Bornean freshwater habitats generally. There is no documented evidence in the available sources of the aquarium trade itself driving population decline, but as with many range-restricted Southeast Asian stream fishes, ongoing habitat pressure is the primary concern.