Crossocheilus is a genus of barbs (family Cyprinidae) native to fast-flowing streams and rivers across Southeast Asia, recorded in the atlas from Thailand, Laos, Cambodia, Vietnam, Malaysia, Indonesia, and China. The atlas covers 2 species, 6.5 in, sharing an elongate, torpedo-shaped body and a ventral, sucker-like mouth built for grazing algae and biofilm off rocks and driftwood in current.
This is one of the most recognized genera in the entire freshwater hobby by reputation: C. oblongus, sold as the Siamese algae eater, is prized above almost any other fish for reliably eating black beard and brush algae that most other algae-eating species ignore. That popularity has a well-known catch for buyers - the "Siamese algae eater" trade name gets applied loosely to several similar-looking fish, including look-alikes from other genera entirely, so correct identification matters for anyone specifically after the true Crossocheilus grazing behavior. C. reticulatus, the silver flying fox, sees far less trade by comparison. Both atlas species are currently assessed Least Concern.