Yunnanilus is a genus of small stone loaches in the family Nemacheilidae, concentrated in Yunnan Province in southwestern China, which gives the genus its name. Species occupy a range of habitats within that region, from flowing hill streams to the springs, sinkholes, and groundwater-fed pools of Yunnan's karst limestone country, and a number of described species are restricted to a single spring system or small lake basin. The atlas covers 33 species with adult sizes from about 1.5–3.5 in, typical of small benthic loaches: slender, low-slung bodies, barbels around the mouth for feeling along the substrate, and a generally subdued brown or grey patterning, though some spring- and cave-associated species show reduced pigmentation and eyes as an adaptation to their sheltered habitats.
Yunnanilus is a genus of far more conservation and scientific interest than aquarium interest; only a small minority of its species, such as the Mini Zebra Loach (Yunnanilus pulcherrimus), have any real presence in the hobby, and most names in the atlas are essentially unknown in the trade. What stands out instead is how threatened the genus is as a whole. The IUCN tally shows a large block of Not Evaluated species alongside a heavy concentration of Endangered and Critically Endangered listings, consistent with a pattern of single-spring or single-lake endemism in a region under mounting pressure from groundwater extraction, spring capping, pollution, and habitat conversion. Several Yunnanilus species are considered among the most range-restricted freshwater fish known anywhere, making the genus a useful bellwether for Yunnan's karst spring ecosystems.