Henicorhynchus caudimaculatus

caudimaculatus: from the Latin cauda, meaning 'tail', and maculatus, meaning 'spotted'.

Recorded from the middle to lower Mekong River basin in southern China (Yunnan province), Laos, Thailand, and Cambodia, plus the Chao Phraya watershed in central Thailand.

Type locality is 'Thailand: Lam Ton Lang, a tributary of Menam Sak [Mae Nam Pa Sak; Ban Lam Thong Lang, village northwest of Pakjong'.

A riverine species most often collected in mid-to-large sized channels, although in the Mekong basin it is also known to enter smaller tributaries and inundated fields.

H. caudimaculatus can be distinguished from congeners by the following combination of characters: presence of a pair of small maxillary barbels, rostral barbels absent; 5-6 faint, thin, lateral stripes along each flank; body depth fits 3.5-3.8 times in SL; 34-35 lateral line scales.

Species currently included in Gymnostomus have previously been placed in a variety of genera including Henicorhynchus, Cirrhinus, Bangana, and Labeo in the last few decades alone. However, Gymnostomus is a senior subjective synonym of Henicorhynchus, thus rendering the latter invalid, while Gymnostomus is easily distinguished from Cirrhinus by possession of 8-9 (vs. 10-15) branched dorsal-fin rays.

Some confusion remains, however, since a recent phylogenetic study (Yang et al., 2012) considered Henicorhynchus to be valid, and members were not recovered in the same evolutionary lineage as Indian Gymnostomus species, suggesting that they are not closely related. It is unclear whether further taxonomic changes will be required in the future in order to reflect this disparity, but here on SF we currently follow Kottelat (2013) since it was published more recently and has been widely accepted, thus Henicorhynchus is a synonym of Gymnostomus.

Gymnostomus species are considered members of the tribe Labeonini within the putative cyprinid subfamily Cyprininae or simply the subfamily Labeoninae (name varies with author). According to the most recent phylogenetic research, this grouping is further divided into four subtribes; Labeoina, Garraina, Osteochilina, and Semilabeoina (Yang et al., 2012). Among these, Gymnostomus is included in the Labeoina alongside Labeo, Bangana sensu stricto (which includes the genus Nukta), Cirrhinus sensu stricto, Cirrhinus microlepis (which is of a different genetic lineage to other Cirrhinus species), and Incisilabeo. As noted above, however, this refers only to the Indian species of Gymnostomus, with the Southeast Asian species placed in the Osteochilina assemblage.

Some Gymnostomus species are common in mainstream rivers at certain times of year and extremely important in local fisheries during these periods.