Dikerogammarus villosus; aquatic species introductions; Ponto-Caspian invader; range extension; Elbe/Labe River basin, Czech Republic

Dikerogammarus villosus, an amphipod crustacean of the Ponto-Caspian origin, was introduced into the Labe (Elbe) River from the Danube River in 1998 after the opening several of man-made canals and by 2001 it had invaded the whole German course of the Elbe and the lower part of Czech course of the river. In September of 2008 D. villosus was found in the Vltava River, a tributary of the Labe (Elbe) River and the biggest river in the Czech Republic. The density and biomass of this species in the Vltava River in September of 2008 reached 214-247 ind. m-2 and 5-7 g wet weight m-2. 40% of specimens in the study population were mature females and around 23% were juveniles (up to 6 mm), which indicates successful conditions for reproduction. D. villosus has become a major component of the macrobenthic fauna in large rivers of the Czech Republic, and further monitoring and assessment of its ecological significance in aquatic communities is warranted