The impact of introduced European catfish (Silurus glanis L.) in UK waters : a three pond study

Invasive fish species pose a threat to native fish species diversity across the globe with the extinction of many native and endemic fish species. There are concerns about the increase in non-native Silurus glanis introductions for trophy angling into the UK and possible harmful impacts to native fish communities. This study aimed to determine a) how different S. glanis size groups may influence establishment success into new environments by using parameters such as growth and trophic alterations and b) the potential risks posed by holding non-native S. glanis. Three ponds and a lake situated in the flood zone to the surrounding river catchment in southern England were used as study sites. A first application in Europe of the European Non-native Species in Aquaculture Risk Analysis (ENSARS) and stable isotope analysis contributed to address the study aims. From this study of the three S. glanis size groups there was a suggestion of differences in growth and trophic impact were correlated with fish size suggesting that life history traits can influence establishment into invaded ponds. Large sized S. glanis exhibited high trophic position in food web which was indicative of an apex predator in pond communities. Across all S. glanis size groups, individuals had distinct differences in isotopic d13C range of diet. This suggests that S. glanis have plasticity in trophic strategy and phenotypic response within new environments which may influence establishment success. The ENSARS analysis distinguished between the potential risks of harmful ecological and socio-economic impacts posed by the likelihood of S. glanis establishment and spread of disease transmission to native fish communities. The analysis suggested that shallow drainage channels and floodplains were likely to be favourable spawning and breeding habitats. A novel ancyrocephalid monogenean parasite Thaparocleidus vistulensis was detected upon S. glanis which was a new finding for the UK. Climate type and habitat niche also influence establishment of non-native fish with predicted thermal changes in aquatic habitats driven by climate change likely to facilitate S. glanis invasiveness into aquatic habitats throughout the UK. Consequently the present risk status of non-native S. glanis invasive potential is liable to change in future years which should be taken into account by updating appropriate risk and regulatory policies in non-native fisheries management.