DNA barcoding of brackish and marine water fishes and shellfishes of Sundarbans, the world's largest mangrove ecosystem

The present study aims to apply a DNA barcoding tool through amplifying two mitochondrial candidate genes i.e., COI and 16S rRNA for accurate identification of fish, aquatic molluscs and crustaceans of Sundarbans mangrove wetland, to build a reference library of fish and shellfishes of this unique ecosystems. A total of 185 mitochondrial COI barcode sequences and 59 partial sequences of the 16S rRNA gene were obtained from 120 genera, 65 families and 21 orders of fish, crustaceans and molluscs. The collected samples were first identified by examining morphometric characteristics and then assessed by DNA barcoding. The COI and 16S rRNA sequences of fishes and crustaceans were clearly discriminated among genera in their phylogenies. The average Kimura two-parameter (K2P) distances of COI barcode sequences within species, genera, and families of fishes are 1.57 +/- 0.06%, 15.16 +/- 0.23%, and 17.79 +/- 0.02%, respectively, and for 16S rRNA sequences, these values are 1.74 +/-.8%, 0.97 +/-.8%, and 4.29 +/- 1.3%, respectively. The minimum and maximum K2P distance based divergences in COI sequences of fishes are 0.19% and 36.27%, respectively. In crustaceans, the K2P distances within genera, families, and orders are 1.4 +/- 0.03%, 17.73 +/- 0.15%, and 22.81 +/- 0.02%, respectively and the minimum and maximum divergences are 0.2% and 33.93%, respectively. Additionally, the present study resolves the misidentification of the mud crab species of the Sundarbans as Scylla olivacea which was previously stated as Scylla serrata. In case of molluscs, values of interspecific divergence ranges from 17.43% to 66.3% in the barcoded species. The present study describes the development of a molecular and morphometric cross-referenced inventory of fish and shellfish of the Sundarbans. This inventory will be useful in future biodiversity studies and in forming future conservation plan.

Automated summary

The present study aimed to use DNA barcoding to accurately identify fish, aquatic molluscs and crustaceans in the Sundarbans mangrove wetland and build a reference library of these species. Through analyzing COI and 16S rRNA sequences, the study found clear discrimination among genera in the phylogenies of fishes and crustaceans. Additionally, corrections in species identification and information on interspecific divergence in molluscs were provided, which will be valuable for future biodiversity studies and conservation efforts.