An eDNA detection of captive-bred Mekong Giant Catfish in the Chao Phraya River basin for further environmental impacts assessment

Abstract

The Mekong Giant Catfish, Pangasianodon gigas, is of great cultural importance for people in Southeast Asia. Over the past century, the population of the species has dramatically declined. Several conservation measures have been taken such as establishing laws to ban catching, conserving the known spawning ground and setting up captive breeding programmes. Interestingly, the captive-bred Mekong Giant Catfish now seems to outnumber the wild population. Detecting the presence of the species is essential but conventional approaches have several limitations. Environmental DNA (eDNA) analysis was used here to detect the Mekong Giant Catfish in the Chao Phraya River basin and reservoirs in the basin. The results from this study clearly show that the eDNA of the Mekong Giant Catfish were found concentrated in the large reservoirs. The concentration of the eDNA of the Mekong Giant Catfish was found to vary among the sites which range from around 31.0–116.8 copy numbers per ml. The Mekong Giant Catfish's eDNA was not detected in water collected from the upstream rivers of the reservoirs but found in the downstream samples. The results reflect those reports of catching the species by locals in the areas. The eDNA detection was proved here to be one of the most efficient, rapid and sensitive methods for the Mekong Giant Catfish monitoring and is now ready to be used if need be.