During the last decade, the situation of Italian fresh waters has been improving in terms of fish abundance due to the general decline in pollution. However, if we were to look to the past and evaluate the state of the fish fauna, we would realize that many species have now disappeared due to a progressive adaptation of alien (non-native) fish in rivers, streams and canals throughout the peninsula. On the one hand, this means that it is increasingly rare to catch the same old fish. On the...