Assessing fish diversity of Merbok Estuary and adjacent marine waters by DNA taxonomy: towards building comprehensive DNA barcode reference library

The Merbok Estuary comprises one of the largest remaining mangrove forests in Peninsular Malaysia. Its value is significant as it provides both direct and indirect services to local and global communities. It also offers a unique opportunity to study the structure and functioning of mangrove ecosystems. However, its biodiversity is still partially described, limiting its research value. Recent inventories based on morphological examination, documented 138 fish species residing, frequenting or subject to entering the Merbok Estuary. Using a molecular approach, we assessed the fish diversity of the Merbok Estuary and its adjacent waters in DNA barcoding 350 specimens assignable to 135 species initially identified based on morphology. Our results revealed the presence of 140 MOTUs, 130 of them are congruent with morphology-based species delimitation. In two cases, barcodes did not permit to differentiate between two morphotypes while they unveiled cryptic diversity within six other species, calling for further taxonomic investigations. This study provides a comprehensive core-list of fish taxa in Merbok Estuary, demonstrating the advantages of combining morphological and molecular evidence to describe diverse but still poorly studied tropical fish communities. It also delivers a large DNA reference collection for brackish fishes occurring in this region which will facilitate further biodiversity-oriented research studies and management activities.