An Insight into the Threadfin (Perciformes: Polynemidae) Diversity of Indian Waters using Mitochondrial COI Signatures

Threadfins (Perciformes: Polynemidae) are commercially important, highly prized table fishes in India. In this study, we analysed the mitochondrial COI gene for validating species identification and phylogeny of threadfins occurring in Indian waters. Consequently, we developed barcodes for ten polynemids belonging to the genera Polydactylus, Eleutheronema, Leptomelanosoma, Filimanus and Polynemus. The K2P distance within the polynemid species in Indian waters ranged from zero to 0.8%. Nucleotide composition was estimated as adenine (A) = 22.5%, thymine (T) = 28.7%, cytosine (C) = 29.7% and guanine (G) = 19.1%. The average transitional pairs (75.8) were more frequent than the average transversional pairs (24.2) with an estimated Transition/Transversion bias (R) of 3.33. Cryptic species were observed in Polydactylus and Eleutheronema indicating the need for detailed studies on the taxonomy of polynemids globally. The present study determines the utility of DNA barcodes in species identification in polynemids.