The increasing distribution of Gammarus roeselii Gervais, 1835: first record of the non-indigenous freshwater amphipod in the sub-lacustrine Ticino River basin (Lombardy, Italy)

This paper reports the first record of the non-indigenous species Gammarus roeselii Gervais,1835 in the sub-lacustrine Ticino River basin (Po river floodplain, Northern Italy). Up to now in Italy, this Balkanian amphipod, known as an “exotic species, well established” in Central Europe, had only been reported in the North-Eastern part of the country (Sile River basin). Gammarus roeselii has a low spreading potential, so its presence in other parts of Europe can only be explained by human activities. However, the available data suggests that its presence in the sub-lacustrine Ticino River basin does not currently represent a threat to the population of the native Echinogammarus stammeri, which is still very healthy in this area.