Nam Ou

The dwarf snakehead, Channa gachua, is a snakehead recorded across an enormous range from Iran to Taiwan and Bali. There is significant evidence that C. gachua as currently understood is a complex of similar-looking species in need of taxonomic review. A mouthbrooder bred regularly in captivity, it can share a well-chosen community with peaceful fishes too large to be prey, but populations should not be mixed as some may hybridise.

Devario laoensis is a devario from the upper Mekong watershed in northwestern Laos and northern Thailand. Its dark P stripe starts faint around mid-body and becomes thicker and darker towards the caudal-fin base. Among congeners it is most similar to D. chrysotaeniatus, in which the P stripe extends to the end of the caudal-fin rays. Its habitats lie at relatively high altitude and are likely to be hill streams and small rivers.

Mystacoleucus greenwayi is a riverine cyprinid from the middle Mekong basin in Thailand and Laos and the Chao Phraya watershed. It favours clear, well-oxygenated running water over sand or gravel, often in rock and boulder-filled headwater streams. A schooling fish, it should be kept in a group of six or more alongside similarly-sized cyprinids, loaches and other riverine fishes, and like all Mystacoleucus it has a forward-pointing predorsal spine that can snag in a net.

Rhinogobius mekongianus is a goby from the middle and upper Mekong basin in Laos, Vietnam and Thailand. Its name has been misapplied in the aquarium trade to the congener R. chiengmaiensis, and it does not appear to have been on the market itself. It has 7-8 irregular dark markings on the body (vs. 5 in R. chiengmaiensis), and records from the Chao Phraya drainage most likely refer to that species.

The goonch, Bagarius yarrelli, is a very large sisorid catfish recorded from the Indus in Pakistan east through Indochina to Sumatra and Borneo. Also known as the 'giant devil catfish' and 'sand shark', it reaches 1300 to 2000 mm and is fished for food across much of its range. That wide distribution appears doubtful, and Indian and Southeast Asian populations may prove not to be conspecific. It lives among boulders in the fast, turbulent rapids of large rivers.

Mekongina erythrospila is a large cyprinid endemic to the middle and lower Mekong River system in Laos, Thailand, Cambodia and Vietnam. It tends to inhabit medium to large river channels with fast-flowing water and rocky beds. Occasionally in the ornamental trade, it grows to 400 to 450 mm and is unsuitable for most private aquaria. It can be aggressively territorial towards conspecifics and similarly-shaped fishes.

Metzia bounthobi is a cyprinid known only from the Nam Ou River basin, a Mekong tributary in northern Laos. It has been collected from hill streams with clear, slow to moderately fast-flowing water. It differs from all its congeners in having more branched anal-fin rays and more lateral line scales, and the genus itself remains unresolved in taxonomic terms.