Mystacoleucus greenwayi

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

greenwayi: named in honour of ornithologist John Greenway (1903-1989), a member of the 1939 French-American expedition to Laos during which the type was collected.

Present in the middle Mekong River basin in Thailand and Laos plus the Chao Phraya watershed in central Thailand. In the latter it is restricted to the Ping, Yom and Nan tributary systems.

Type locality is 'Ban Nam Khueng, 30 km northwest of Ban Nam Khueng, about 6 km from Mekong River, Laos'.

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.

In the Mun River, close to the Pak Mun dam, Thailand, sympatric species included Hampala dispar, Cyclocheilichthys apogon, Osteochilus hasseltii, Kryptopterus apogon, K. bleekeri, Acanthopsis choirorhynchus, Raiamas guttatus, and Puntioplites proctozysron.

In a small stream of the Nam Ou river watershed, Phôngsali Province, northern Laos it occurred sympatrically with Acheilognathus deignani, Cyprinus rubrofuscus, Devario laoensis, Pseudorasbora parva, and Barbodes semifasciolatus.

An aquarium with base dimensions of 120 ∗ 45 cm48 ∗ 18 in or equivalent should be the minimum size considered.

Choice of décor is not as critical as water quality and the amount of open swimming-space provided but this species is perhaps best-suited to an environment resembling a flowing stream/river with a substrate of variably-sized, water-worn rocks, sand, fine gravel and perhaps some small boulders.

This can be further furnished with driftwood roots or branches, and aquatic plants such as Microsorum, Bolbitis or Anubias spp. can be grown attached to the décor.

Since it naturally occurs in pristine habitats it is intolerant to accumulation of organic pollutants and requires spotless water in order to thrive. Though torrent-like conditions are unnecessary it also does best if there is a high proportion of dissolved oxygen and moderate water movement. Weekly water changes of 30-50% aquarium volume should be considered mandatory.

Likely to be a generalised omnivore in nature. Stomach analyses of the congener M. marginatus showed it to feed on insects, crustaceans, worms, algae and aquatic plants, though it's unclear if the latter two were taken directly or via the stomach contents of prey items.

In the aquarium it is easily-fed but for it to develop its best colours and condition offer regular meals of small live and frozen foods such as chironomid larvae (bloodworm), Daphnia and Artemia along with good quality dried flakes and granules; at least some of the latter should contain added plant material such as Spirulina.

Not aggressive but can upset slow-moving or timid tankmates with its vigorous behaviour, especially when feeding, so is best maintained alongside robust, similarly-sized fishes, especially cyprinids, loaches and other riverine species.

This species exists in schools in the wild therefore a group of six or more should be the smallest considered.

Sexually mature females are likely to be deeper-bodied than males.

Unrecorded in aquaria. In nature spawning occurs during the wet season, from April to September.

M. greenwayi can be distinguished from congeners by the following combination of characters: body relatively slender, depth fitting 3.3-3.5 times in SL; 28-31 +2 lateral line scales; 14 circumpeduncular scale rows; one pair of maxillary barbels; dorsal-fin with black distal margin; numerous body scales with a dark, crescent-shaped marking on the base.

All Mystacoleucus species possess a procumbent predorsal spine orientated towards the head, though it can be difficult to spot with the naked eye. Thos 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's 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.