The qPCR results of Asian arowana eDNA detection in Muda Lake, Kedah, Malaysia

We present a qPCR-based eDNA method to detect the presence of the endangered Asian arowana (Teleostei: Osteoglossidae: Scleropages formosus) in Muda Lake, where resides one of its last wild populations on the west side of Peninsular Malaysia. Flanked by a pair of newly developed species-specific primer, a 163-base pair fragment of the cytochrome oxidase subunit I (COI) gene was selected as the eDNA marker. We applied our eDNA method at five sampling sites throughout Muda Lake and at five different periods. 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.