Investigation of the genetic diversity of pearl spot, Etroplus suratensis (Bloch, 1790), through DNA barcoding and phylogenetic analysis from two habitats

Abstract

Etroplus suratensis (pearl spot) is a commercially important cichlid native to South and Southeast Asia, yet its genetic variation in habitats of Karnataka has not been previously studied. This study integrates morphological and molecular approaches to examine specimens from freshwater (n=65) and brackish water (n=60) environments. Morphometric and meristic analyses confirmed species identity, but significant differences in several characters (p < 0.05) were observed between the two populations, likely reflecting phenotypic plasticity driven by environmental conditions. Such variation may cause ambiguity in species identification if based solely on morphology. Mitochondrial cytochrome c oxidase I (COI) gene sequences (655 bp) were amplified and compared with GenBank references. BLAST analysis confirmed  E. suratensis identity, and phylogenetic reconstruction revealed strong genetic homogeneity, with an average intraspecific divergence (K2P) of 0.005. Both populations clustered closely with published E. suratensis sequences, indicating minimal genetic differentiation despite pronounced morphological differences. This study represents the first genetic diversity assessment of E. suratensis from Karnataka and provides essential baseline data on its population structure. Our findings highlight the limitations of morphology-based identification in phenotypically variable species and recommend DNA barcoding for accurate species validation in ecological monitoring, fisheries management, and conservation. Future research should investigate adaptive genomic variation and environmental influences on phenotypic traits to better understand the species' evolutionary adaptability across habitats. Keywords COI gene, DNA barcoding, Etroplus suratensis, Genetic diversity, Morphometry, Phenotypic plasticity, Karnataka