Known from the middle Mekong basin in Laos and Thailand, and may be endemic to the Khorat Plateau. Records exist from the Mun and Songkhram watersheds in northeastern Thailand, and a number of Mekong tributaries in laos, including the Nam Mang and Nam Kou drainages.

Type locality is ‘Nam Mang downstream of Ban Thabok, between 18°22’25″N, 103°13’30″E, and about 1 kilometer upstream, Vientiane Province, Laos’.

Native to the Mekong River drainage in Laos (where Vientiane province represents the upper limit of its range), Thailand, Cambodia, and Vietnam, and the Tapi, Chao Phraya, and Mae Klong systems in Thailand.

Type locality is ’22 kilometers upstream from Phnom Penh, Tonle Sap River, Kandal Province, Cambodia’.

Known from various parts of the middle and upper Mekong river basins with record existing from the Nam Tha, Nam Ou, Nam Khan, Nam Lik, Nam Ngum and Nam Mang tributary systems in Laos, the Nam Noeua (a tributary of Nam Ou) in Vietnam, and the Mae Nam Kok in Thailand.

Occurrences in the Chao Phraya drainage in central Thailand most likely refer to the congener R. chiengmaiensis.

This species is among a handful of near-identical congeners that are traded as ‘Siamese algae-eater’ (often abbreviated to ‘SAE’), ‘Siamese flying fox’ and ‘Crossocheilus siamensis’.

The latter name is not valid, however, and is a synonym of Epalzeorhynchos siamensis which is itself a synonym of Crossocheilus oblongus, a species described from Java. C. oblongus is currently accepted to…