Description of a new <i>Pangasius</i> (Valenciennes, 1840) species, from the Cauvery River extends distribution range of the genus up to South Western Ghats in peninsular India

A new species of the genus Pangasius, is described based on 17 specimens collected from the Cauvery River, India. It can be distinguished from its sister species from South and Southeast Asia, by its widely placed, small and rounded vomerine and palatine tooth plates, longer maxillary and mandibular barbels, greater vertebrae count 50 (vs. 44-48), and smaller caudal peduncle depth (6.5-8.2% SL vs. 9.89-13.09% SL). The tooth plates of the new species closely resembles that of Pangasius macronema but can be clearly distinguished from the latter by having lesser gill rakers (16-19 vs. 36-45); a smaller eye (2.4-4.4% SL vs. 5.2-9.6% SL); and larger adipose-fin base (1.5-2.9% SL vs. 0.1-1.2% SL). The mitochondrial cytochrome c oxidase (COI) gene sequence of the new species shows the genetic divergence of 3.5% and 5.1% from P. pangasius and P. silasi respectively, the two sister species found in South Asia and India. The species delimitation approaches, Poisson Tree Processes (PTP) and assemble species by automatic partitioning (ASAP) clearly resolved that the P. icaria is distinct from its sister species. Phylogenetic position of the species with its sister species was evaluated using maximum likelihood and Bayesian analysis. The discovery of this previously unknown species of genus Pangasius from the Cauvery River of peninsular India indicates important biogeographical insight that this genus migrated till the southern division of Western Ghats.