Invasion patterns of the monster wels catfish (Silurus glanis) in spanish freshwater ecosystems and development of new molecular tools for its early detection

Abstract

One of the most important threats to Spanish freshwater ecosystems are non-indigenous species (NIS). They could produce a high impact on the survival of native species as a consequence of competition for limited resources and environmental changes. The giant wels catfish Silurus glanis, was intentionally introduced in Spain in 1974 and, since then, it has had an alarming and hidden spread in Spanish basins due to its consideration as a fishing trophy, specially in the last fifteen years. In this work, we have updated the invasive pattern of S. glanis through Spanish freshwater ecosystems since the first introduction until nowadays. For that purpose, we compiled all the official and non-official information about the spread of this catfish in Spain. The current situation reflects its presence in six of the seven main river basins in the Spanish territory. Also, we have designed genus specific primers with Prise2 to be used as a tool for PCRs allowing detection of this species in environmental DNA (eDNA) (a technique that allows the detection of remaining species DNA in water). They were tested on eDNA samples extracted from experimental aquariums and on real environmental samples taken from different basins in Spain (Ebro, Douro, Tagus). In all of these basins we were able to detect S. glanis. Official Silurus reports were confirmed with two molecular markers in five out of the six cases (83%) assayed in this work, and in two out of three non-officials reports coming from fishermen websites and newspaper reports. The eDNA method can be a helpful tool in the fight against this controversial and dangerous invasive species. It can be used for its early detection allowing fast and effective stakeholders management actions.