Invaders they are a-changing(dagger): A recent, unexpected surge of invasive loaches in Catalonia

Risk analyses for invasive species often assume that the characteristics of future invaders will resemble those already successful, but these features may change. Here, we use data from more than 3,500 fish sampling events, sequencing of mitochondrial and nuclear genes and analyses of several traits describing non-native fish to describe the irruption and rapid expansion of non-native loaches in Catalonia, north-east Iberian Peninsula, and framing this surge in the knowledge of previous invasions. We report the establishment of at least five (Cobitis bilineata, Misgurnus anguillicaudatus, Misgurnus bipartitus, Paramisgurnus dabryanus, and a yet undescribed Barbatula species) non-native loach species in Catalonia, most of which are currently spreading. Furthermore, one of the two regionally native loach species (Cobitis paludica) has been introduced and is spreading through river basins where it is not native. Genetic analyses were fundamental to understand loach invasions, by clarifying specific statuses, identifying the origin of non-native populations and/or detecting independent introduction events. Genetic results also highlighted the unresolved taxonomy of loaches, particularly for European Barbatula. Loaches are recent, diverse, and successful invaders whose traits differ from those of most previously established invasive fish species, signalling potential weaknesses of prevention of biological invasions based on prohibited species lists. We call for the development of more flexible management tools (e.g. based on fish traits and not only on species identities) and prioritising prevention and rapid responses to new introductions.