Protomyzon is a genus of hillstream loaches native to fast-flowing forest streams on Borneo and neighboring parts of Southeast Asia; the atlas's records span Malaysia, Indonesia, and Brunei. Like other hillstream loaches, Protomyzon species have a flattened body and modified paired fins that act as a sucker, letting them cling to smooth rocks in strong current rather than being swept downstream. The four species in the atlas are small, with adults ranging from about 1.5–3 in.
Hillstream loaches as a group have a dedicated following among aquarists who build cool, well-oxygenated, fast-flow 'stream' tanks with powerheads and rocky substrate, but Protomyzon species specifically are seen far less often in the trade than more common hillstream genera, and none of the atlas's four species has a widely used common name on record. Conservation status is reassuring so far — three species are rated Least Concern and one is Not Evaluated — though hillstream specialists in general remain sensitive to water quality and flow changes in the fast, clear streams they depend on.