# Catching common carp with eDNA in Thailand’s rivers

## TL;DR

This study used eDNA to track common carp in Thailand's rivers, showing their widespread presence and the effectiveness of eDNA as a monitoring tool.

## Contribution

The study demonstrates the utility of eDNA and Bayesian modeling for tracking invasive fish in tropical rivers.

## Key findings

- eDNA detection rates increased from 80% in 2022 to 96% in 2024.
- Occupancy probabilities remained stable, but eDNA concentrations suggest increased biomass.
- eDNA is a reliable and scalable method for monitoring invasive fish.

## Abstract

Common carp (Cyprinus carpio) 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.

•eDNA reveals widespread common carp across Thailand’s rivers•Detection rates increased from 2022 to 2024 while occupancy remained stable•False-positive-aware occupancy modeling improves confidence in detections•eDNA offers scalable monitoring for invasive fish in tropical river systems

eDNA reveals widespread common carp across Thailand’s rivers

Detection rates increased from 2022 to 2024 while occupancy remained stable

False-positive-aware occupancy modeling improves confidence in detections

eDNA offers scalable monitoring for invasive fish in tropical river systems

Ecology; Environmental biotechnology; Ichthyology; Aquatic biology