Diversity and distribution of fish in rivers Chinnar and Thenar and their tributary, southern Western Ghats, Tamil Nadu, India

The diversity and distribution of fishes were studied in the Chinnar and Thenar rivers of the Cauvery River basin of Anamalai Hills. A total of 14 sampling sites were randomly selected in this region, and fish sampling was carried out from April 2017 to May 2018. The high species diversity was recorded in downstream site 11, Thenar River (H’ = 3.14), and low diversity was observed in upstream site 3, Chinnar River (H’ = 1.64). Thirty-seven species of primary freshwater fishes belonging to four orders, 11 families, and 21 genera were recorded. The order Cypriniformes, with 26 species, dominate the fish assemblages (70.27%), followed by Perciformes with six species (16.21%), Siluriformes with four species (10.81%), and Synbranchiformes with one species (2.70%), respectively. Among the Cyprinids, Devario aequipinnatus, Barilius getensis, and Garra mullya had the highest local dominance (32% each) in this river’s cape. The only one exotic species, Oreochromis mossambicus, was recorded at downstream sites of Amaravathi River. Among the recorded species, about 43% of fish species are endemic to the Western Ghats, seven species are listed as threatened, five as endangered, and two are vulnerable, according to the IUCN Red List.