Monitoring the eradication of the highly invasive topmouth gudgeon ( Pseudorasbora parva ) using a novel eDNA assay

Aquatic invasive species (AIS) represent an important threat for Biodiversity and are one of the factors determining the ecological integrity of water bodies under the Water Framework Directive. Eradication is one of the most effective tools for the management of invasive species but has important economic and ecological trade‐offs and its success needs to be carefully monitored. We assessed the eradication success of the topmouth gudgeon ( Pseudorasbora parva ), an invasive fish that poses significant risks to endemic aquatic fauna, in four ponds previously treated with the piscicide Rotenone using a novel qPCR‐based environmental DNA (eDNA) assay. We validated the assay through successfully detecting DNA from topmouth gudgeon in two reservoirs with physically confirmed topmouth gudgeon populations. Topmouth gudgeon were detected in all four treated ponds using 750 ml water samples and in three of the ponds using 15 ml samples, despite the eradication treatment and lack of successful detection using conventional trapping methods. Our results highlight the difficulties of eradicating invasive fish and the need to incorporate reliable monitoring methods as part of a risk management strategy under the water framework directive (WFD).