Being able to consistently and comprehensively monitor aquatic biodiversity is critical to inform fisheries management and evaluate the effectiveness of conservation actions. For large tropical rivers like Southeast Asia’s Mekong – which spans six countries and is home to over a thousand species of fish – the logistical and physical challenges of sampling the full range of diversity in the system are daunting to say the least. But the key to achieving this colossal effort may be microscopic. Environmental DNA, or eDNA, is rapidly proving itself to be an invaluable tool for monitoring biodiversity, particularly for fish communities. However, it has only just begun to be applied in diverse tropical river systems, and has yet to be comprehensively evaluated in the Mekong Basin. But that is about to change, as FISHBIO and the Cambodian group Young Eco Ambassador (YEA) have recently undertaken a pilot effort funded by the Wonders of the Mekong Project to conduct eDNA sampling at a landscape scale across the lower Mekong and its tributaries in Cambodia. The results from this study will represent an important first step for understanding the types of questions that eDNA analysis may help answer in the Mekong, which in turn may pave the way for its integration into fisheries monitoring programs in the region.

 

Environmental DNA techniques rely on the detection of genetic material that living things shed into their environment, and collecting an eDNA sample is as simple as pushing river water through a very fine filter to capture particles that may contain DNA. Because collecting eDNA samples is inexpensive and can be done rapidly, this technology represents a potentially powerful opportunity to efficiently collect a significant amount of data across very large landscapes. Monitoring with eDNA has already been extensively applied in temperate river systems, and has yielded valuable information for fisheries managers. Further, comparisons of eDNA data with data obtained from traditional sampling methods (like nets and traps) have shown promise for this technique to effectively capture fish community diversity. Although eDNA methodology has been successfully implemented for the detection of rare species in the Mekong, including the Mekong Giant Catfish (Pangasianodon gigas), the use of eDNA to capture a “snapshot” of all the fish present in an area has not been broadly tested in the region, and indeed has only just begun to be used in tropical river systems. This community approach to eDNA relies on a methodology known as metabarcoding, in which fragments of DNA from a specific region of the mitochondrial genome are amplified. Variations in these sequence fragments can be used to identify the species that shed the DNA in question, and in this way many species can potentially be identified from a single water sample.