Morphological and molecular evidence for range extension and taxonomic validation of Sperata aorides (Jerdon, 1849) in the Western Ghats, India

Sperata aorides (Jerdon, 1849) is a commercially important freshwater catfish endemic to the Cauvery River basin, including its tributary, the Bhavani River. The present study report a range extension of the species to the Bharathappuzha River in Kerala, documenting its previously unrecorded distribution based on morphometric and molecular evidence. Specimens for the study were collected from different river systems in the Western Ghats, including the type locality at Erode, Tamil Nadu. Morphometric comparisons revealed minor variations between populations in head proportions, particularly in interorbital distance (19.5-24.5% vs 15.8-22.1% in HL) and eye diameter (12.0-17.3% vs 8.8-17.9% in HL). Mitochondrial cytochrome c oxidase subunit I (COI) gene sequencing confirmed species identity. Phylogenetic analysis showed that S. aorides forms a distinct clade, with low intraspecific genetic divergence (0.19%) between Cauvery and Bharathappuzha populations and higher divergence (4.61-9.85%) from congeners. These findings confirm the taxonomic validity of S. aorides and extend its known distribution to the Bharathappuzha River in the southern Western Ghats. Keywords: Bharathappuzha, Catfishes, COI gene sequencing, Distribution, Tamil Nadu