Mystacoleucus lepturus

Mystacoleucus: from the Ancient Greek μύσταξ (mústaks), meaning 'upper lip, moustache', and the generic name Leuciscina, which is not currently in use.

lepturus: from the Ancient Greek λεπτός (leptós), meaning 'slender, thin', and οὐρά (ourá), meaning ‘tail’, presumably in reference to this species' relatively slender caudal peduncle.

Known only from the upper Mekong River basin in southern China (where the river is known as Lancang Jiang), Laos, and Thailand. Records from Vietnam and Hainan Island are incorrect and refer to other species.

Type locality is 'Tributary of Lancang Jiang, Mengna (Mengla) Xian, Xishuangbanna, Yunnan Province, China'.

Predominantly a riverine fish favouring clear, well-oxygenated, running water with substrates of sand or gravel and often present in rock and boulder-filled headwater streams.

This species can be distinguished from congeners by the following combination of characters: body relatively slender, depth fitting 3.4-3.8 times in SL; 32-33 + 2 lateral line scales; 14 circumpeduncular scale rows; presence of a single pair of barbels; black distal margin on dorsal-fin; numerous body scales with dark, crescent-shaped markings.

All Mystacoleucus species possess a procumbent predorsal spine orientated towards the head, though it can be difficult to spot with the naked eye. This can become entangled in an aquarium net so care must be taken when handling the fish.

The trait is shared by members of Tor, Spinibarbus and Paraspinibarbus although there exists no strong evidence to suggest that these genera form a monophyletic lineage and it is likely that they developed the spine independantly of one another. Mystacoleucus spp. can be further identified by the presence of 6-10 branched anal-fin rays and 24-39 lateral line scales.