Gastromyzon

Gastromyzon is a genus of small, freshwater loaches in the order Cypriniformes. Traditionally placed in the family Balitoridae, it is also treated by some classifications as the subfamily Gastromyzontinae within the family Gastromyzontidae. The genus comprises numerous described species that inhabit fast-flowing streams. Members exhibit dorso-ventrally flattened bodies, broad heads, a ventral, downward-facing mouth adapted for grazing on rock surfaces, and stout fins that aid in clinging to substrates in turbulent water. They are typically small, reaching roughly 3–6 cm in length, though sizes vary.

Geographic distribution covers parts of Southeast Asia and southern China, including Vietnam, Laos, Cambodia, Thailand, Malaysia, Indonesia, and Borneo. Their habitats are clear, well-oxygenated streams with rocky or gravel substrates and strong currents, often in mountainous or hilly terrain.

Ecology: Gastromyzon species feed mainly on algae and biofilm scraped from rocks and other submerged surfaces. Their suction-like mouths and modified fins enable them to resist being swept away. Many species shelter in crevices or under overhangs. Reproductive biology is not well documented in detail; it is assumed that eggs are adhesive and laid in rocky crevices, with limited parental care as in related hillstream loaches.

In the aquarium hobby, a few species are kept by enthusiasts who replicate fast-flowing, oxygen-rich conditions with ample aeration, power heads, and rocky substrates. Conservation concerns stem from habitat degradation, siltation, and damming that can diminish suitable hillstream habitats.