Epalzeorhynchos is a small genus of Southeast Asian cyprinids - the barb and carp family - native to the Mekong and Chao Phraya drainages of Thailand and neighbouring Cambodia, Laos, and Vietnam. The atlas's 2 species share a torpedo-shaped, laterally flattened body, a flat ventral surface, and a downturned, sucker-like mouth fringed with barbels, built for grazing algae and biofilm off rocks in fast-flowing rivers. They run 4.5–6 in, and both are strongly territorial toward their own kind.
Both species are hobby staples, sold under names that reference their coloring rather than taxonomy: the redtail shark (Epalzeorhynchos bicolor), jet-black with a vivid orange-red tail, and the rainbow shark (E. frenatum), grey-brown with red-tinged fins. Despite huge captive-bred numbers in the trade, the wild picture is dire for one of them - the redtail shark is Critically Endangered, reduced to a small stretch of central Thailand and squeezed by damming, sand mining, and pollution, and is one of the atlas's CARES-listed species. The rainbow shark, by contrast, remains Least Concern.