Taxonomy & naming
Rhyacoschistura larreci was formally described by the Swiss ichthyologist Maurice Kottelat in 2019 in the journal Zootaxa, based on a holotype of 2 in standard length and a paratype of 2.5 in standard length, both collected from the Nam Houng watershed, part of the Mekong drainage in Xayaburi Province, Laos. The species epithet honours LARReC, the Living Aquatic Resources Research Center, marking that institution's twentieth anniversary at the time of description.
It belongs to the genus Rhyacoschistura, a small group within the family Nemacheilidae — the stone and brook loaches, by far the largest and most species-rich family in the loach superfamily Cobitoidea. The genus name itself points to the group's habits: it combines a root referring to torrents or mountain streams with the loach genus name Schistura, signalling that these are fast-water specialists within the broader Schistura-like radiation. As with much of Nemacheilidae, the genus-level classification here has been repeatedly revised as older, broad genera such as Nemacheilus and Noemacheilus were split apart; Rhyacoschistura larreci has only ever been described under its current combination, so there is no historical synonymy to untangle for this particular species.
Morphology
Rhyacoschistura larreci is a modestly sized nemacheilid, with both known specimens just under 2.5 in standard length — consistent with the compact size typical of stream-dwelling stone loaches. The original description notes a color pattern of numerous narrow, slanted bars crossing the flank in an irregular arrangement, rather than the bold, evenly spaced banding seen in some other loach groups. Males have modified, branched pectoral-fin rays with a notably thickened first ray, and the pelvic-fin morphology is described as distinctive — features used to separate this species from its close relatives within the genus.
Like other nemacheilids, it almost certainly carries the family's characteristic near-scaleless or fine-scaled skin, a trait that makes stone and brook loaches generally sensitive to strong medications and heavy metals in the aquarium. The original description does not describe an erectile suborbital spine of the kind seen in the botiid loaches, and none should be assumed here — that structure belongs to a different loach family. Beyond the diagnostic features recorded in the type description, detailed morphological data for this recently described species remain sparse.
Habitat
The type locality is the Nam Houng watershed, a tributary system within the Mekong drainage in Xayaburi Province in northern Laos — a landscape of fast-flowing, clear hill streams draining forested terrain. No population data beyond the type series has been published, so the species' full range within the wider Mekong basin is unknown.
As a member of Rhyacoschistura — a genus name that itself signals a torrent-dwelling lifestyle — and of the broader Nemacheilidae, this fish is inferred to inhabit cool-to-moderate, well-oxygenated, fast-flowing hillstream water over sand, gravel and stone, in the manner typical of the family. This is not a still-water or blackwater species; stone and brook loaches of this kind are found where the current runs and the water stays clear and richly oxygenated. Precise temperature and chemistry readings from the type locality have not been published, so any aquarium parameters should be treated as an informed estimate for a Southeast Asian hillstream loach rather than a measured fact.
Feeding
No dietary study has been published for Rhyacoschistura larreci specifically. Nemacheilid stone and brook loaches as a group are benthic micro-predators and grazers, working the streambed for small invertebrates, insect larvae and crustaceans, and taking algae and organic detritus opportunistically; many are most active at dusk and after dark.
On that basis this species should be treated as a small-invertebrate feeder rather than a herbivore or a flake-eater. In an aquarium setting it would be expected to take small live and frozen foods such as bloodworm, daphnia and brine shrimp readily, alongside sinking pellets formulated for bottom-dwelling fish, while showing little interest in food that stays at the surface.
Mating
Nothing has been published on courtship or spawning behaviour in Rhyacoschistura larreci. No external sexual dimorphism is described in the original account beyond the modified pectoral- and pelvic-fin structure noted as diagnostic of the species — features that may relate to sex or simply to species identification, and the type description does not clarify which.
Stone and brook loaches of this kind are, as a family, egg-scattering fish with no courtship display or pair bond reported; spawning in related species is understood to be tied to seasonal rises in flow rather than any elaborate mating ritual. In the absence of direct observation for this species, that general pattern is the best available guide.
Breeding
There is no record of Rhyacoschistura larreci being bred in captivity, and as a recently described species from a single remote Laotian stream system, that is unsurprising. Nemacheilid stone and brook loaches as a family are egg-scatterers: ripe adults release eggs over gravel and among stones in fast-flowing water, with no nest, no guarding and no parental care of any kind — a very different strategy from the cave-guarding or mouthbrooding behaviours seen in some other fish groups, which do not apply to this genus.
Given the total absence of husbandry or spawning data, the honest summary is that this species is not known to have been bred in the aquarium, and any reproduction in captivity would rely on replicating cool, fast, highly oxygenated flowing water rather than any specific triggering technique that has been documented.
In the aquarium
Rhyacoschistura larreci is not established in the aquarium trade, and there is no husbandry record to draw on. Anything said here is inference from its genus and family rather than from keeper experience with this species. As a small hillstream-adapted nemacheilid, it would be expected to need cool-to-moderate, clear, fast-flowing, well-oxygenated water over a sand-and-gravel substrate with rounded stones — closer to a powerhead-driven biotope tank than a typical still community aquarium.
Like other near-scaleless loaches, it should be assumed sensitive to copper-based medications and to full-strength doses of many standard treatments, so any medicating would call for caution and reduced dosing. Given the size of the type specimens, under 2.5 in, a modestly sized but strongly filtered and well-aerated setup would suit it, ideally with the company of its own kind, since social grouping is a general trend across small benthic loaches even where it has not been specifically documented for this species. At present, though, this remains a scientific description rather than an aquarium fish.
Conservation
Rhyacoschistura larreci has not been assessed by the IUCN Red List and is classified here as Not Evaluated. As a species described only in 2019 from a single watershed in a remote part of Laos, it fits a common pattern among newly described stone and brook loaches: real, named, and yet essentially unstudied beyond the original description.
With no population estimate, no known range beyond the type locality, and no documented trade presence, no conservation status can honestly be assigned beyond Not Evaluated. Its home region — the Mekong basin's tributary streams in northern Laos — faces broader regional pressures from damming, deforestation and water development that affect many Mekong-basin endemics, but no specific assessment of impact on this species has been published.