Taxonomic triage of the genus Thrissina from Indian waters: a step towards diversity assessment

Anchovies of the genus Thrissina (family Engraulidae) are common pelagic fishes that constitute a high-volume fishery resource along the Indian coast. Their accurate identification is essential for the fishery and management of resources. 314 specimens of six species of the genus Thrissina were collected to generate data for exact field identification and species-specific molecular signatures. The identification of the specimens was confirmed using morphometric and meristic parameters, along with COI-based DNA barcodes. This integrative study also aimed to reconstruct a phylogeny to clarify the evolutionary relationships among the species. The morpho-meristic results indicated that maxillary length, number of scutes, number of lower gill rakers, and anal fin ray count were the main characteristics for identifying Thrissina species. The species barcoded included T. setirostris , T. malabarica , T. mystax , T. baelama , T. polybranchialis , and T. vitrirostris . The nucleotide content of each species was examined and the genetic distance was calculated. The interspecific genetic distance (K2P) ranged from 13–22% with the highest distance observed between T. baelama and T. malabarica (22%) and the lowest between T. mystax and T. polybranchialis (13%). The average genetic distance within the genus was 19%. The topology of the phylogenetic tree showed that all the species in this study formed separate clades with a common ancestor. This work provides the first COI-barcode of the least investigated T. polybranchialis from the Indian coast, and establishes the relationship between T. mystax and T. polybranchialis . The integrative data generated here will aid in the correct identification and global studies on the genus. More morphological and molecular studies are recommended to clarify the relationship between all available species within this genus.