Metzia bounthobi

Metzia: named for Charles William Metz, Stanford University, who helped authors identify fishes collected in Japan.

bounthobi: named "in honour of Bounthob Praxaysombath (NUOL), who was the leading researcher performing the field surveys throughout the NUOL-NEF project on 2007–2010. Eight of all 10 type series of the new species were brought from the project surveys".

Known only from the Nam Ou River basin, a Mekong tributary in Phongsaly and Luang Prabang provinces, northern Laos.

Type locality is 'Mekong basin in Sopvan, Nyoi District, Luang Prabang Province, Lao PDR (20°36.5’N, 102°39.1’E), northern Laos'.

Collected from hill streams with clear water and slow to moderately fast-flowing water.

This species can be distinguished from congeners by the following combination of characters: 18–20 (vs. 10-18) branched anal-fin rays; 49–55 (vs. 35-48) lateral-line scale rows; 33–36 (vs. 15-20) predorsal scale rows; 20–22 (vs. 14-18) circumpeduncular scale rows; 8–10 (vs. 12-18) gill rakers on outer side of the first gill arch.

Although it is included in the genus Metzia this grouping remains somewhat unresolved in terms of taxonomy and it may contain more than a single genetic lineage. For example, members share a number of characters with the genera Ischikauia Jordan and Snyder 1900, Hemiculterella Warpachowski 1887, and several species of Anabarilius Cockerell 1923, including a bipartite gas bladder, a non-spinous dorsal-fin ray, and a sharp ventral keel between the pelvic-fin insertion and anus.

Metzia was also recovered together with the genus Hemigrammocypris in a phylogenetic study published in 2010, thus rendering it paraphyletic. In addition, M. formosae and M. longinasus differ from most other members of the genus in mouth position (upturned vs. terminal in putative congeners) and number of lateral line scales (43–48 vs. 35-39), and M. bounthobi differs from all congeners in number of branched anal-fin rays (18-20 vs. 10-18) and lateral line scales (49-55 vs. 35-48).

The current concept of Metzia can be diagnosed as follows: body compressed; abdomen with a sharp ventral keel between pelvic-fin insertion and anus; no barbels; no symphysal projection on the lower jaw fitting into a depression on upper jaw; lateral line complete, curved ventrally anterior to pelvic-fin insertion, running parallel with ventral profile and extending through centre of caudal peduncle above anal-fin base; gas bladder bipartite, posterior chamber with a rounded distal extremity; last simple dorsal-fin ray not spinous, origin closer to caudal-fin base than tip of snout or posterior to a vertical through pelvic-fin insertion; 10-20 branched anal-fin rays; 35-55 lateral-line scales.