Taxonomy & naming
Acanthopsoides robertsi was described by Siebert in 1991, one of a handful of species placed in the genus Acanthopsoides — a group of small, horseface-shaped loaches within the family Cobitidae, the true spined loaches. The genus name itself signals its relationship to the better-known horseface loach genus Acantopsis: Acanthopsoides means, roughly, "resembling Acanthopsis," and the two genera share the same elongated snout and sand-diving habit, differing mainly in scale counts, fin details and adult size.
The Catalog of Fishes (Eschmeyer, CAS) is the authority for the currently valid combination, Acanthopsoides robertsi, and no synonymy or generic transfer is in wide use for this species. It sits within Cobitidae, the family that gives all true loaches their defining feature: an erectile spine hidden in a groove beneath the eye, used defensively and folded away when not needed.
Morphology
This is a small, slender, torpedo-shaped loach with the elongated, slightly upturned snout typical of the horseface group — an adaptation for probing and burrowing into sand. Seriously Fish records a maximum standard length of around 2 in, translating to roughly 2.5–3 in total length including the caudal fin, making it distinctly smaller than the well-known horseface loach Acantopsis dialuzona, which it superficially resembles. The Aquarium Wiki similarly gives a maximum of about 2 in.
Like all Cobitidae it carries the family's signature erectile suborbital spine, folded into a groove beneath the eye and flicked out defensively when the fish is stressed or handled. Its scales are minute and deeply embedded, leaving the skin functionally naked — a trait shared across the true loaches that makes them notably sensitive to medications and slower to recover from skin damage than scaled fish.
Habitat
Acanthopsoides robertsi is endemic to the island of Borneo, known from the Kapuas River basin in West Kalimantan, Indonesia, with the type locality given as an oxbow of the Kapuas near 0°44'N, 112°23'E. The Aquarium Wiki also notes records from forest and upland streams in the wider Indonesia–Malaysia border region of Borneo, generally in moderate-to-fast-flowing water over sandy bottoms.
This is a tropical species through and through, living in warm, flowing streams and river channels with sandy or fine-gravel substrates — exactly the kind of soft, loose bed a sand-sifting loach needs to bury into and forage through. It is not a coldwater or temperate Cobitidae like the Eurasian spined loaches or the dojo; its water and thermal requirements track the warm lowland and upland rivers of equatorial Borneo.
Feeding
Acanthopsoides robertsi is a sand-sifting benthic omnivore. In the wild it forages by burying into fine sand and sieving worms, small arthropod larvae and organic detritus out of the substrate through its gills — the same feeding strategy used by its larger relative Acantopsis, just on a smaller scale. This is a fish built to work loose sediment, not to pick food off gravel or rock.
In the aquarium it readily takes sinking foods: frozen or live Artemia, Tubifex, Daphnia and bloodworm are all reported to suit it well. Because natural feeding depends on a soft, diggable substrate, a bed of fine sand lets the fish express its normal foraging behaviour and find missed food; on gravel or coarse substrate it can only pick at what lands on the surface, which shortchanges both its diet and its wellbeing.
Mating
No reliable account of sexual dimorphism in Acanthopsoides robertsi has turned up in the available sources — the sexes are not reported to differ obviously in colour or body shape, which is typical for small horseface-type Cobitidae and makes pairing by eye difficult for keepers.
As a tropical Bornean stream species, any natural spawning cue would be tied to the seasonal rains and associated changes in river flow, much as with other Southeast Asian Cobitidae — but no observed spawning behaviour, wild or captive, has been documented for this species in the sources consulted.
Breeding
Acanthopsoides robertsi has not been bred in home aquaria as far as the available sources record. Seriously Fish notes that breeding is undocumented for this species, though an unrelated species sold under the trade name Acanthopsoides sp. "A01" has reportedly spawned once in captivity, with fry recorded over a mixed sand and fine-gravel substrate — a data point about the genus's general habits rather than a confirmed account for A. robertsi itself.
Like other tropical Cobitidae — the horseface loaches (Acantopsis) and Lepidocephalichthys — this species falls outside the pattern seen in temperate spined loaches such as Cobitis, Sabanejewia and the dojo (Misgurnus), which have been pond- or tank-spawned in cooler climates. Where any Cobitidae does spawn, the mode is egg-scattering over or among plants and fine substrate with no parental care; there is no cave-guarding or mouthbrooding in this family. For Acanthopsoides robertsi specifically, the honest picture is that it is essentially never bred by hobbyists, and any captive-bred stock reaching the trade would be exceptional rather than routine.
In the aquarium
Acanthopsoides robertsi is described by The Aquarium Wiki as a peaceful, sociable bottom-dweller, well suited to a quiet community of similarly small, non-aggressive fish. Its modest adult size — around 2–3 in — makes it far less of a long-term space commitment than its larger horseface relatives, but it still needs the same core setup: a soft, fine sand substrate it can bury into and sift, moderate to strong water flow reflecting its stream origins, and good oxygenation.
Being a true loach, it carries the family's near-scaleless skin and the associated sensitivity to copper-based medications and full-strength treatments generally; half-doses and gentle, loach-safe products are the safer route if disease treatment becomes necessary. As with most Cobitidae this species is not commonly available in the trade and is best sought from specialist loach or Bornean-fish importers rather than general fish stores; the Aquarium Glaser importer profile in the source material confirms it does periodically enter the commercial supply chain from Indonesia.
Conservation
Acanthopsoides robertsi has not been formally assessed on the IUCN Red List and is recorded here as Not Evaluated (NE) rather than assigned a guessed status. Multiple searches across IUCN, GBIF, WorldSpecies and ITIS turn up no published assessment for this species.
It is known only from a limited area of the Kapuas basin in West Kalimantan and the wider Bornean stream systems noted by The Aquarium Wiki, which — as with many small-range Bornean freshwater endemics — leaves it potentially exposed to the broader pressures facing the island's rivers: deforestation, agricultural conversion and associated sedimentation. No population trend or trade-driven decline has been documented for this species in the available sources, and its low profile in the aquarium trade means collection pressure is likely minor compared to habitat change.