Gyrinocheilus is a genus of Southeast Asian freshwater fish placed in its own family, Gyrinocheilidae, within the order Cypriniformes alongside the true loaches. The atlas covers 3 species, native to fast-flowing rivers and streams in Cambodia, Laos, Thailand, and Vietnam. What sets the genus apart from ordinary loaches is its feeding apparatus: a specialized, disc-like sucking mouth used to clamp onto rocks and rasp off algae, paired with an extra water-intake opening above each gill so the fish can keep breathing while its mouth stays fixed to the substrate — a genuine anatomical workaround rather than a simple sucker-mouth. Unlike most Cypriniformes, Gyrinocheilus also lack barbels around the mouth.
Gyrinocheilus aymonieri, at roughly 11 in, is the species most aquarists know by sight even if not by name: sold worldwide as the 'Chinese algae eater' or 'Siamese algae eater,' it is a classic starter fish bought young for its enthusiastic grazing on tank algae. The catch is well documented in the hobby — as it matures it grows territorial and often stops grazing altogether, switching instead to rasping the mucus coat off slower tankmates, a behavior that has made adult specimens a common rehoming problem. G. pennocki and G. pustulosus, by contrast, are little-known regional species that rarely if ever reach the trade. Two of the genus's three species have not yet been formally assessed for conservation status.