“There are bigger ones,” he says before killing it, as required by law as it is an invasive exotic species. The wels catfish — the largest freshwater fish in Europe, which can reach a length of 2.5 meters and weigh over 120 kilos — has not stopped multiplying and wreaking environmental havoc since the German biologist Roland Lorkowsky introduced 32 fry from the Danube into the Segre river, in the Ebro basin, in 1974.