The Irrawaddy River, also names Ayeyarwady River, is a river that flows throughout South-Eastern Asia. The Irrawaddy drainage area in China is originating from Tibet and is consisted of three branches, the Dulongjiang River, Dayingjiang River and Longchuanjiang River.
The Irrawaddy River is home to a large diversity of animals, including about 43 fish species. Based on the previous research, it is the type locality of seven species of Schizothorax, including S. molesworthi meridionalis, S.myzostomus, S. dulongensis, S. elongates, S. oligolepis, S. oligolepis malacathus and S. rotundimaxillaris.
In a recent study conducted by Dr. CHEN Xiaoyong (Kunming Institute of Zoology, CAS) and his colleagues, two species never previously described were identified during taxonomic works on Schizothorax species distributed in the Irrawaddy drainage area in China, and were named Schizothorax leukus sp. nov. and Schizothorax heteri sp. nov.
Schizothorax leukus can be distinguished from its congeners by a combination of the following characters: surface of lower lip covered with papilla, posterior edge of lower lip straight; low jaw developed, almost full the oral cavity, anterior edge of low jaw covered with horny sheath; breast and belly before pectoral-fin tip scaleless; barbels equal to eye diameter; last un-branched dorsal fin ray soft, lower third of the ray enlarged with posterior edge serrated; lateral line scales 94–105, scales between dorsal-fin origin to lateral line 26–34, scales between pelvic-fin origin to lateral line 21–27; outer side of the first gill arch with 16–20 gill rakers; body dark brown, without dark spots.
Schizothorax heteri can be distinguished from its congeners by a combination of the following characters: rostral fold equal to upper lip; lower lip developed, trilobed, the median lobe minute, its width equal to diameter of the rostral barbel base; postlabial groove continuous; low jaw without horny sheath; breast and belly before pectoral-fin tip scaleless; barbels equal to eye diameter; last un-branched dorsal fin ray strong, posterior edge serrated; dorsal-fin origin posterior to pelvic-fin origin; lateral line scales 89–104, scales between dorsal-fin origin to lateral line 24–33, scales between pelvic-fin origin to lateral line 19–29; body light brown, without any spots.
Moreover, in this study, the validation of S. rotundimaxillaris and the questionable records of S. molesworthi, S. griseus and S. paoshanensis were discussed. So far, eight valid species of Schizothorax were found and recorded from the Chinese Irrawaddy drainage.
The main findings of this study have been published on Zoological Research (http://www.zoores.ac.cn/CN/abstract/abstract3366.shtml).