Labiobarbus siamensis

Labiobarbus: from the generic names Labeo and Barbus.

siamensis: 'from Siam' [Thailand].

Known from the Mekong River system in Laos, Thailand, and Cambodia, plus the Chao Phraya and Bang Pakong watersheds in central Thailand.

Type locality is 'Thailand: Petschaburi [Petchaburi] and Bangkok'.

Inhabits rivers and streams of all sizes, and typically moves into inundated floodplains and forests during the wet season.

Wild fish are known to feed on small items including phytoplankton, zooplankton, periphyton, and benthic algae.

L. siamensis can be distinguished from congeners by the following combination of characters: 39-42 scales in the lateral series; shoulder spot usually absent, but sometimes well-defined; body with longitudinal stripes formed by a spot on each scale; dorsal fin with dusky median stripe and no red coloration; caudal fin dusky, sometimes with reddish coloration, but no well-defined stripes; 20-23 circumpeduncular scales; 25-30½ branched dorsal-fin rays; maxillary barbels relatively long, extending well beyond posterior border of eye.

Different populations vary in appearance somewhat (see image of Salween specimen for example), and L. leptocheilus may turn out to represent a group of closely-related species rather than a single taxon. The population from the Cambodian Mekong has been considered to represent a distinct species, Labiobarbus lineatus, although that name is currently a synonym of L. leptocheilus following Kottelat (2013). However, it is widely used in the ornamental trade, and typically applied to all forms of L. leptocheilus.

In recent studies the genus Labiobarbus is usually grouped within the cyprinid subfamily Labeoninae. Several authors including Roberts (1989) have argued that the generic name Dangila (Valenciennes, 1842), which was officially used for over 100 years, should continue to take precedence.

However according to rules set out in the modern-day International Code of Zoological Nomenclature Labiobarbus is the correct name on the basis of priority, having first been proposed by van Hasselt in 1823. Further doubts that van Hasselt and Valenciennes may have described two different fish were settled by Roberts (1993) who found that they were the same.

Members are most-easily distinguished from their close relatives by the possession of two pairs of well-developed barbels, an extremely long dorsal-fin with 4 simple and 18-30 branched rays and unique soft mouth parts which lack unculi (these form ridge-like rows on the lips of other Labeonins).