Abstract

1. The topmouth gudgeon Pseudorasbora parva has proved to be a highly invasive pest fish species in mainland Europe following introduction from Asia, and was first recorded in the wild in the UK in 1996. Distribution has increased markedly since 2002, with recordings now from 32 sites, the majority being lakes. 2. In infested UK lakes, populations establish rapidly and become dominant in the fish community (often >97% by number); densities to over 60 m-2 have been recorded, with the majority of individuals <70 mm. The species also hosts a novel pathogen not previously recorded in the UK. It has, therefore, been identified as a significant concern to native fish communities and deserving of an appropriate response by regulatory authorities. 3. Where populations have been detected in lakes with connection to river catchments, actions have been taken to prevent riverine dispersal. Control measures are put in place, and eradication programmes designed and initiated. This paper details case studies on three completed eradication operations, two that utilized the piscicide rotenone, the other, de-watering and disinfection. 4. Each case study has, so far, been successful in eradicating the topmouth gudgeon population and has resulted in approximately 280 km of river length being protected from their dispersal. Application of rotenone was the most cost-effective eradication method at approximately £2 per m2 of water area treated. 5. These case studies demonstrate that riverine dispersal of invasive fish from infested connected lakes can be prevented by eradication. Outputs can be used to develop a strategy to manage the increasing distribution of topmouth gudgeon - and other invasive, pest fish - in the UK.