DNA barcoding of feral tilapias in Philippine lakes

Tilapia (Oreochromis mossambicus) was first introduced to the Philippines in 1950 for aquaculture. Since then, other species of tilapia have been introduced to the country and some of them (mainly Oreochromis niloticus) have become established in lakes and other water bodies. In this study, DNA barcoding using the mitochondrial cytochrome c oxidase subunit I (COI) gene was done to assess the reliability of morphological identification and the degree of introgression among feral tilapias (Oreochromis spp.) in seven major Philippine lakes, namely Laguna de Bay, Lake Lanao, Taal Lake, Lake Mainit, Lake Naujan, Lake Bato, and Lake Buhi. Specimens were also collected from a private hatchery in Sual, Pangasinan to serve as reference. Morphological traits, Nucleotide BLAST (BLASTn), and Translated BLAST (BLASTx) analyses were used to classify the specimens. A Neighbor-Joining tree was constructed using the Kimura 2-Parameter method, incorporating 66 COI sequences generated from the study and 20 additional reference sequences obtained from GenBank. Three Oreochromis clusters were obtained and were classified as the O. niloticus group, O. mossambicus group, and O. aureus group, with bootstrap support values of 99%, 74%, and 99%, respectively. The mean K2P genetic distances within each group were 0.008%, 0.959%, and 0.086%, respectively. The clustering of COI sequences generated from this study corresponded with the results of the BLASTn analysis. Oreochromis hybrids were also found in all the lakes. The study highlights the usefulness of DNA barcoding for molecular identification and detection of introgressed individuals, with potential applications in management of feral stocks.