Taxonomy & naming
Yunnanilus discoloris was described by Zhou and He in 1989, placed from the outset in Yunnanilus — a genus of small stone loaches named for Yunnan province, where many of its species are endemic. It sits within Nemacheilidae, the stone and brook loach family, which was split out of the old, unwieldy "Noemacheilus/Nemacheilus" catch-all as ichthyologists worked through the immense diversity of small-bodied loaches across Asia. The Catalog of Fishes is the authority for the currently valid combination, Yunnanilus discoloris.
The species epithet discoloris is Latin for "differently coloured" or "of two colours," referring to the marked colour difference between males and females rather than to any single striking pattern. As with many Yunnanilus species, it is known almost entirely from its type locality and has attracted little taxonomic revision since its original description; the literature on it remains thin, a pattern typical of the genus's many narrow-range spring and stream endemics.
Morphology
Like other Yunnanilus, this is a small, slender, nearly scaleless stone loach built for gripping and browsing along the bottom of clear, flowing water. Nemacheilids of this genus typically carry the small, erectile suborbital spine characteristic of true loaches, and their skin is thin and largely naked of scales — a feature that leaves them notably sensitive to medication and to poor water quality. FishBase's account gives no specific size or weight for the species, and no photograph is on record there; general knowledge of the genus does not extend far enough to responsibly estimate this species' proportions or maximum length, so no figure is given here rather than guessing.
The one morphological detail that is well documented is sexual dimorphism, and it is striking for a nemacheilid: males show a black longitudinal stripe running down the flanks with light spots strung along the back, while females instead show black spotting and blotching scattered across the back and flanks. This is an unusually clear-cut pattern difference for a stone loach and is presumably part of what the describers had in mind when they named the species "differently coloured."
Habitat
Yunnanilus discoloris is endemic to a single spring — known as White Dragon Spring — and its outflow near Chenggong, on the edge of Kunming in Yunnan province, southern China. The spring drains into Lake Dianchi, the large plateau lake that sits at the heart of the Kunming basin. This places the species firmly within the Yunnan-Guizhou Plateau ichthyofauna, a region famous among ichthyologists for producing narrow, spring-bound endemics found nowhere else.
As a stone loach of a spring-fed system, it can be expected to live in cool, clear, well-oxygenated water typical of the habitat type — the springs and spring-runs of the Yunnan plateau are markedly cooler and cleaner than the region's larger, more turbid rivers. Beyond that general expectation for the genus and habitat, FishBase and the other sources consulted give no further detail on substrate, flow or water chemistry at the site, and none should be invented; the honest picture is a single, small, largely undocumented spring habitat under direct threat from its lack of protection.
Feeding
No species-specific diet data for Yunnanilus discoloris were found in the sources consulted. Stone and brook loaches in Nemacheilidae are, as a rule, bottom-foraging micro-predators, working over gravel and stone for small invertebrates — insect larvae and tiny crustaceans — in place of anything resembling a grazing or filter-feeding strategy, and it is reasonable to expect this species follows that general pattern.
Given how little is documented about this fish, that expectation should be read as a genus-level generalisation rather than a confirmed fact about Yunnanilus discoloris itself. Data on its feeding ecology is genuinely sparse, and this atlas would rather say so plainly than fabricate specifics that no source supports.
Mating
No courtship or spawning behaviour has been documented for this species in the sources reviewed. What is known is limited to the sexual dimorphism itself — males carrying a black flank stripe with pale dorsal spotting, females instead showing dark spotting and blotching — which at least confirms that the sexes are visually distinguishable, a useful starting point that most small stone loaches do not offer.
Beyond that, nothing in the record describes how or when this population spawns in the wild, and no aquarium spawning has been reported. As with feeding, the honest position is that mating behaviour in Yunnanilus discoloris is essentially unstudied.
Breeding
There is no documented aquarium breeding record for Yunnanilus discoloris, and given how narrowly it is known — a single unprotected spring, a population under 500 individuals, and no meaningful presence in the hobby — that is unsurprising. Stone and brook loaches in Nemacheilidae are, as a family, egg-scatterers: ripe fish release eggs over gravel and among stones in fast water, with no nest-building, no cave-guarding and no parental care once the eggs are laid. That is the general pattern for the genus, and there is no reason to expect this species departs from it, but it has not been confirmed for Yunnanilus discoloris specifically.
In practice, this is a species that has essentially never been bred in captivity, and the honest expectation for any keeper is that it will not be either — both because of the general difficulty of breeding small nemacheilid loaches at home and because so little is known about its specific spawning triggers and behaviour.
In the aquarium
Yunnanilus discoloris has no meaningful presence in the aquarium trade, and none of the sources consulted offer species-specific care guidance, tank size, temperature or water-chemistry recommendations. Rather than borrow figures from an unrelated genus or fabricate a care sheet this species has never earned, this atlas records that the aquarium picture for Yunnanilus discoloris is essentially blank.
What can be said comes from the wider biology of Nemacheilidae and of near-scaleless loaches generally: fish of this build tend to be sensitive to copper and to full-strength medication, and stone loaches from cool, clean, flowing spring or stream habitats generally fare poorly in warm, still, high-bioload community tanks. Given that the wild population is critically small and the species is not established in the hobby, any responsible keeper encountering material claiming to be Yunnanilus discoloris in trade should treat the identification with real scepticism — and the conservation case against removing spring-endemic fish from a population already under 500 individuals should weigh heavily against collection.
Conservation
Yunnanilus discoloris is assessed by the IUCN as Critically Endangered, a status that reflects both its extraordinarily narrow range and the precariousness of that single site. It is known only from White Dragon Spring near Chenggong, Kunming, and its outflow into Lake Dianchi; the estimated total population is fewer than 500 individuals, and the spring itself is not protected. An academic paper — "Threatened fishes of the world: Yunnanilus discoloris," published in Environmental Biology of Fishes — has specifically flagged the species' threatened status, underscoring that its precarious situation has been recognised in the scientific literature, not just by a red-list entry.
A species restricted to one unprotected spring on the edge of a rapidly urbanising city — Kunming, one of southern China's largest metropolitan areas — faces exactly the kinds of pressures that push narrow endemics to extinction: groundwater extraction, pollution, habitat modification and simple encroachment. There is no evidence that the aquarium trade plays any role in its decline; the threat here is habitat, not collection. With no protected status for the spring itself, the species' survival depends entirely on whether that single water body persists in a condition the fish can tolerate.