Tracking the tropical aquatic dragon: environmental DNA (eDNA) detection for monitoring the endangered Asian arowana, Scleropages formosus (Müller and Schlegel, 1840)

We present a quantitative polymerase chain reaction (qPCR)-based eDNA method to detect the presence of the endangered Asian arowana, Scleropages formosus (Müller and Schlegel, 1840) (Teleostei: Osteoglossidae), in Muda Lake where one of its last wild populations remains on the west side of Peninsular Malaysia. We first developed and tested a 123-base pair S. formosus-specific genetic marker using a new pair of primers. Then we applied our eDNA method at five sampling sites throughout Muda Lake and at five different months. The study observed a marked seasonal variation in detection rates, with significantly higher rates during the wet months of August, January, and December compared to the dry season spanning May and June. The Asian arowana is known to breed during the rainy season and we therefore hypothesize its reproductive biology influences the concentration of eDNA in the lake. Our results also highlight the possible impact of abiotic factors in tropical freshwater ecosystems (such as high water temperature) on eDNA persistence. In conclusion, future applications of qPCR-based eDNA methods in tropical environments would benefit from locally evaluating the effects of both biotic and abiotic factors on species detection.