Catching common carp with eDNA in Thailand’s rivers

Common carp (<i>Cyprinus carpio</i>) are both ecologically disruptive invaders and economically important aquaculture species in Thailand. This study applied environmental DNA (eDNA) analysis with digital PCR (dPCR) and Bayesian occupancy modeling to assess carp distribution across five major river systems from 2022 to 2024. eDNA was detected at 80% of surveyed sites in 2022, increasing to 96% by 2024, with higher concentrations particularly in the Nan and Ping rivers. Occupancy probabilities remained relatively stable across years, while rising eDNA concentrations indicate greater detectability and possible local increases in biomass. Detection probabilities were high at both field and laboratory stages, confirming methodological reliability. While aquaculture escapes and hydrological drivers are plausible influences, these factors were not directly tested. The findings provide robust baseline evidence of widespread persistence of common carp in Thailand's rivers and highlight the potential of eDNA as a scalable, cost-effective tool for freshwater monitoring and management.