Taxonomy & naming
Neonoemacheilus labeosus was described by the Swiss ichthyologist Maurice Kottelat in 1982, part of his extensive early work sorting out the Nemacheilus/Noemacheilus complex — historically an enormous catch-all genus for small Asian stream loaches that has since been split into Schistura, Barbatula, Triplophysa, Neonoemacheilus and many others. The genus name itself signals this history: Neonoemacheilus, "new Noemacheilus," was erected to hold species that did not fit cleanly into the older, broader genera once everything was being scrutinised more closely.
The species sits in the family Nemacheilidae, the stone and brook loaches — by species count the largest family in the loach superfamily Cobitoidea, and one still being actively revised. The Catalog of Fishes is the governing authority for the valid combination, and it is currently recognised there as Neonoemacheilus labeosus. According to Loaches Online, the genus is very small, containing only one other described congener, N. peguensis, which underscores how narrow and specialised this taxonomic slice of Nemacheilidae is.
Morphology
This is a small, slender stone loach, reported by FishBase to reach a maximum of about 4 in standard length — modest even by the standards of the small-bodied Nemacheilidae. Its defining feature is the mouth region: very thick, fleshy lips ring a distinct pre-oral cavity, and the mouth itself opens posteriorly, on top of that cavity, rather than facing directly downward or forward as in most stream loaches. This unusual arrangement is the character most consistently singled out in the available descriptions of the species, and it likely reflects a specialised way of taking food off hard, current-swept surfaces.
Like other nemacheilids, Neonoemacheilus labeosus carries the family's characteristic small, elongated, near-scaleless body built for holding position in fast water, and — as in most stone loaches — an erectile spine below the eye is part of the family's toolkit for deterring predators and, incidentally, for snagging carelessly-handled nets. Beyond the distinctive mouth, detailed morphometric data for this species is sparse in the available literature.
Habitat
Neonoemacheilus labeosus is native to the Salween river basin, with a documented range spanning northeastern India, Myanmar and Thailand. FishBase lists it as a demersal freshwater species, meaning it lives and feeds on or near the streambed rather than in open water. Consistent with most Nemacheilidae, it is a fish of clear, flowing streams rather than still, sluggish water.
Loaches Online records the practical water parameters kept for the species: a temperature range of 72–79 °F, pH from about 6.0 to 7.5, and soft-to-medium hardness (up to roughly 12 dH). It calls for a decent flow rate and good oxygenation, mirroring the well-aerated, moving streams of its native basin. A suitable setup uses fine sand mixed with smooth pebbles and includes hiding spots such as bogwood or slate — the structure of a clear hill or foothill stream rather than a soft, still, blackwater habitat.
Feeding
FishBase places the species at a trophic level of about 2.8, close to that of a primary consumer, which is broadly consistent with a benthic micro-predator/grazer feeding low on the food web rather than an active hunter of larger prey. Its unusual thick-lipped, posteriorly-set mouth is suggestive of grazing or rasping food from stream substrates, a feeding style Loaches Online explicitly compares to that of the algae-grazing genus Garra, though this is inferred from mouth shape rather than documented directly from gut-content studies.
In the aquarium, Loaches Online reports that it accepts sinking pellets, and readily takes live and frozen foods such as bloodworm, brine shrimp and daphnia. A varied diet that includes some grazing opportunity — biofilm on smooth stones or bogwood — likely suits it best, echoing its natural habit of working over hard streambed surfaces.
Mating
Almost nothing has been documented about courtship or spawning behaviour in Neonoemacheilus labeosus. FishBase notes only a fragment of reproductive data: females of 2–2.5 in standard length were found carrying ovulae 0.5 in in diameter, confirming that fish in this size range are reproductively mature, but no spawning season, courtship behaviour or fecundity data have been documented for the species.
Given its placement within the stone and brook loaches, any spawning that does occur is expected to follow the family's general pattern of scattering eggs over gravel or stones in flowing water with no pair-bonding or nest-building — but this has not been directly observed or recorded for this species, and it would be dishonest to present it as confirmed fact rather than a reasonable inference from its relatives.
Breeding
There is no record of Neonoemacheilus labeosus having been bred in the aquarium. Loaches Online states plainly that no spawning has been reported in captivity, and the species is not known to have entered the ornamental fish trade in any meaningful way — it remains extremely rare in the hobby, if present at all.
As with the great majority of stone and brook loaches, the expected mode — based on the family and on the limited wild reproductive data available — is that of an egg-scatterer over gravel or stones in fast-flowing water, with no parental care. This is inference rather than direct observation for this specific species: the honest position is that its breeding biology is essentially undocumented, and it should not be expected to spawn in a typical home tank.
In the aquarium
Neonoemacheilus labeosus is not established in the aquarium trade, and very little practical keeping experience has been written up for it. What guidance exists points to a small, current-loving stream loach: Loaches Online recommends a decent flow rate with good oxygenation, water in the 72–79 °F range with a pH of 6.0–7.5 and soft-to-medium hardness, and a substrate of fine sand mixed with smooth pebbles, supplemented with bogwood or slate for cover. This mirrors the clear, flowing, foothill-stream conditions of its native Salween basin — not a warm, still, heavily-planted community tank.
As with most small, near-scaleless nemacheilids, caution with medications is a reasonable default even though it is not specifically documented for this species: stone loaches as a group tend to be sensitive to copper and to full-strength treatments. Given its rarity in the hobby, a keeper who does encounter this species should expect to be working with very little established precedent, and should prioritise strong flow, high oxygenation and a varied, partly grazing-based diet over any community-tank convenience.
Conservation
Neonoemacheilus labeosus is assessed by the IUCN Red List as Least Concern, with the assessment dated 10 October 2011. It occupies a documented range across northeastern India, Myanmar and Thailand within the Salween basin, and Loaches Online notes it is not known to have entered the ornamental trade in any real numbers, meaning collection for the aquarium hobby is not a documented pressure on the species.
As with much of the freshwater fauna of the Salween basin, the broader long-term risks facing this species are likely to be habitat-driven — damming, water abstraction and land-use change across the basin — rather than any trade-related decline, though detailed population trend data specific to this species is not available in the sources consulted here.