Taxonomy & naming
Acanthopsoides delphax was described by the ichthyologist Siebert in 1991, in a revision of the genus Acanthopsoides that drew on existing museum collections to distinguish several previously conflated species. The genus name places it among the dwarf horse-faced loaches, a group closely allied to the true horse-faced loaches, Acantopsis, within the family Cobitidae — the spined and pond loaches. The Catalog of Fishes, the standing authority for valid fish names, retains the combination Acanthopsoides delphax.
The species epithet delphax is Greek for 'piglet,' a fitting diminutive for a fish that tops out at only about 2.5 in and sits within a genus whose species are notoriously difficult to tell apart even for specialists. As with much of the Cobitoidea, the group has been repeatedly reshuffled since the nineteenth century; Acanthopsoides itself was only clearly separated from Acantopsis in relatively recent taxonomic work, and this species should be regarded as a genuinely obscure, seldom-studied member of the family.
Morphology
Acanthopsoides delphax is a small, elongate true loach with the long, pointed snout characteristic of its genus — reported at roughly 1.9 to 2.1 times the length of the head, an exaggerated, horse-like face shared with its relative Acantopsis. Its color pattern is faint and unremarkable by loach standards: a pale body marked chiefly by two small black blotches at the base of the caudal fin, without the bold banding seen in showier cobitids.
As a member of family Cobitidae it carries the erectile suborbital spine that defines the group — a small, sharp spine housed in a groove beneath the eye that can be flicked out defensively, and that gives the family its common name of spined loaches. Like other true loaches its skin is functionally near-scaleless, with tiny, deeply embedded scales, a feature that matters for medication sensitivity. Maximum recorded size is small: about 2.5 in standard length, making this one of the more diminutive members of the family.
Habitat
This is a tropical Southeast Asian species, native to the Mekong, Salween and Chao Phraya river basins — a range spanning parts of mainland Southeast Asia rather than any single country's watershed. It inhabits slow-current stretches of rivers over muddy to sandy substrate, the kind of soft, fine bottom that its genus is built to exploit.
The species shows potamodromous behavior, meaning it undertakes wholly freshwater migrations within river systems rather than moving to sea. It is unambiguously a warm-water, tropical fish — not a coldwater or temperate species like the Eurasian spined loaches (Cobitis, Sabanejewia) or the dojo loach (Misgurnus) — and it should be kept and understood accordingly, in warm, soft, slow-flowing water over a fine substrate.
Feeding
Acanthopsoides delphax is a benthic omnivore, foraging over and within the soft riverbed for small invertebrates. Like its close relative the horse-faced loach Acantopsis, its long snout and elongate body are suited to working through muddy or sandy sediment rather than picking food from hard surfaces, sifting out worms, insect larvae, small crustaceans and other benthic prey along with some detritus.
A soft substrate is not optional for this feeding style — it is how the fish is built to find food. Any aquarium attempt to keep this species would need to replicate that soft, sift-able bottom rather than relying on gravel or bare glass, offering a mixed diet of sinking foods that reach the substrate where the fish actually forages.
Mating
No courtship or spawning behavior has been documented for Acanthopsoides delphax specifically; the species is data-sparse even by the standards of a poorly known genus. What can be said comes from its position within family Cobitidae and its tropical, Southeast Asian range, which puts it in the same broad camp as other tropical cobitids such as Acantopsis and Lepidocephalichthys rather than the temperate Cobitis, Sabanejewia or Misgurnus lineages that have occasionally been pond-spawned in captivity.
Given the total absence of published breeding accounts, no sexual dimorphism has been reported and none should be assumed; this is an area where honest silence is more useful than invented detail.
Breeding
As a member of family Cobitidae, this species' relatives are egg-scatterers: ripe fish release adhesive eggs among plants or vegetation, typically around spring conditions, with no parental care afterward. Several temperate spined loaches — Cobitis, Sabanejewia, and the dojo or weather loach Misgurnus — have been pond- or tank-spawned by hobbyists and researchers under cooler, seasonal conditions. The tropical Cobitidae, including the horse-faced loaches Acantopsis and species of Lepidocephalichthys, have generally not been bred in captivity, and Acanthopsoides delphax falls squarely into that unbred, tropical branch of the family.
There is no documented spawning of Acanthopsoides delphax in the aquarium or in research settings. The honest picture is that this species has essentially never been bred in captivity, and any breeding account attributed to it should be treated with skepticism absent a citable source.
In the aquarium
Acanthopsoides delphax is not an established aquarium fish; it is a small, seldom-imported, difficult-to-identify member of a genus that even specialists struggle to tell apart from its close relatives. Any keeper attempting it should plan around its real biology: a soft, sand-like substrate for natural sifting behavior, warm tropical water matching its Mekong-Salween-Chao Phraya origins, and slow to moderate current reflecting the sluggish river stretches it inhabits.
As with other true loaches, its near-scaleless skin makes it sensitive to copper-based medications and full-strength treatments generally — half-doses and gentle products are the safer default for any cobitid. Given its modest 2.5 in adult size, a species-appropriate setup would not need to be large, but the near-total absence of husbandry reports means most specifics — ideal group size, compatible tankmates, longevity — remain genuinely unknown rather than merely unwritten here.
Conservation
Acanthopsoides delphax has not been evaluated by the IUCN Red List and carries no conservation category; it is recorded here as Not Evaluated rather than assigned a guessed status. This is unsurprising for a small, taxonomically obscure river fish within a genus whose species are difficult even to distinguish from one another.
No population trend, threat assessment or trade data specific to this species is documented in the sources consulted. Its native basins — the Mekong, Salween and Chao Phraya — face well-known broader pressures from damming, sedimentation and land-use change across mainland Southeast Asia, but attributing any specific impact to this species without a formal assessment would be guesswork rather than fact.