DNA barcoding of the ichthyofauna of Taal Lake, Philippines

Everyone may be familiar with barcodes usually printed as parallel lines in labels of most commercial products. It is basically a machine-readable representation of data that makes possible the efficient management and accurate retrieval of information about the product. Now, instead of parallel lines, imagine using a short genetic marker in the organism’s DNA sequence as the barcode, then we have what is referred to as DNA barcoding.

DNA barcoding is a method to identify an organism as belonging to a particular species using short, standardized gene regions. It is used to identify an unknown sample by comparing the barcode with a known classification.  It is also useful in discriminating specifies of highly similar morphology, flagging certain specimens for further taxonomic analysis, and assisting in the discovery of new species.

In a recent study [1], a team of researchers from the University of the Philippines in Diliman, Divine Word College of Legaspi, and Angeles University Foundation used DNA barcoding to identify the different species of fish found in Taal Lake. The study represents the first molecular survey of the ichthyofauna of Taal Lake and the first DNA barcoding attempt of Philippine fishes. The findings of the study appeared in a recently published paper entitled “DNA barcoding of the ichthyofauna of Taal Lake, Philippines” by SVL Aquilino and colleagues in the journal Molecular Ecology Resources.

Located in the province of Batangas, Taal Lake is the third largest lake in the Philippines (the largest being Laguna de Bay) and is considered a very important fisheries resource. It provides freshwater fish to the country and is also home of the world’s only freshwater sardine, Sardinella tawilis. The rampant introduction of foreign fish species into the lake, however, has caused the lake’s declining biodiversity, which could be due to competition, direct predation, or hybridization. In fact, it has been reported that 87% of the previous listings of fish species had disappeared during the same time that aquaculture flourished in the lake [2]. This makes DNA barcoding relevant as it would provide some definitive information on the species of fish that can be found in the Taal Lake ecosystem.

In the study, 23 species of fish taken from the lake were barcoded. Of the 23 species, one is Sardinella tawilis, which is endemic to Taal Lake, 15 are native to the Philippines, and seven are introduced. The study’s general findings showed an “increasing genetic variation with increasing taxonomic levels, supporting a marked change in genetic divergence at the species boundaries”. DNA barcoding also revealed some new information which either confirms species demarcation or warrants further taxonomic reexamination. For example, the studied specimen of halfbeaks were found to be closest to Hyporhamphus affinis instead of Hyporhamphus quoyi, as previously reported. The study was also the first to report five new species, namely Hyporhamphus affinis, Sarotherodon melanotheron, Amphilophus citrinellus, Glossogobius aureus and Awaous melanocephalus, which were not reported in the lake before. The researchers suggested that the first two must have been recently introduced, while the latter three could have been misclassified in previous reports.

The results presented in the paper provide some evidence in the effectiveness of DNA barcoding for the rapid and accurate identification of fishes and for identifying certain species that need further taxonomic investigation. More importantly, it also provides a better understanding of the fish ecology of Taal Lake, which could serve as a baseline information for policy makers in creating better conservation strategies or in aiding them in their efforts to effectively manage the lake.

Details of the study can be read in “DNA barcoding of the ichthyofauna of Taal Lake, Philippines” by S. Aquilino, et al. Molecular Ecology Resources 11 (2011), pp. 612–619.

References:

1. Aquilino SVL, Tango JM, et al. DNA barcoding of the ichthyofauna of Taal Lake, Philippines, Molecular Ecology Resources 11 (2011), pp. 612–619.
2. Papa RDS, Pagulayan RC, Pagulayan AEJ, Zooplanktivory in the endemic freshwater sardine, Sardinella tawilis (Herre 1927) of Taal Lake, the Philippines, Zoological Studies 47 (2008), pp. 535–543.