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The spread of invasive fish species poses a major threat to native aquatic communities and ecosystems. Amur sleeper is one of the most rapidly spreading invasive fish in Eurasia. In this study, we used environmental DNA (eDNA) metabarcoding to sample fish assemblages in various types of water bodies in a protected floodplain of the Middle-Danube section in Hungary, with a special attention to the distribution patterns and early detection of the invasive Amur sleeper. The species was detected in one of the 15 water bodies sampled. At this site all samples were tested positive for the species and the detection was additionally confirmed by electrofishing. This is the first detection of the species in this Danubian floodplain. Since the area maintains a high level of biodiversity with numerous protected and rare aquatic invertebrates and vertebrates, we highlight the need of urgent management actions to prevent the further spread of Amur sleeper within and outside of the floodplain. Additionally, we provide a further example of the practical application of eDNA methods in the early detection of invasive species. [ABSTRACT FROM AUTHOR]

The introduction and spread of alien fish species pose a major threat to native communities and ecosystem functioning in freshwaters. Black bullhead is one of the most successful invaders in European waters with several detrimental effects on native biota and ecosystems. In this study, we used stable isotope analysis to compare the body size and season-dependent diet, trophic position, isotopic niche size, and niche overlap of the invasive black bullhead with two native fish species (roach and European perch) in Lake Balaton, Hungary. We found that black bullhead could be characterized by invertivore-piscivorous feeding habit with a high rate of fish consumption. The rate of fish predation by invasive black bullhead increased with body size, while no seasonal differences were observed in fish consumption. Contrary to our hypothesis, little evidence of actual feeding competition was found between black bullhead and native fishes. Our results suggest that the studied species assimilate distinct energy resources in different proportions leading to a substantial amount of niche partitioning among them. We conclude that black bullhead may represent a threat for native, small-sized fishes primarily through predation and recommend urgent management actions (e.g. selective removal of the species) to minimize its adverse impacts on native communities. [ABSTRACT FROM AUTHOR]

This study presents the first occurrence and recent distribution pattern of the river nerite (Theodoxus fluviatilis L., 1758) in Lake Balaton. The first appearance of this Prosobranch snail was recorded along the western shore of the Tihany peninsula situated on the middle section of the lake, at 21st of October 2013 during a routine macrozoobenthos sampling. Occurrence of the species was also recorded along the eastern shoreline of the peninsula in 2015, and it became highly abundant in both areas in the following years. Results of a comprehensive survey conducted in the autumn of 2018 in the littoral region of the lake revealed that the river nerite has colonized almost the entire shoreline of Lake Balaton, only the westernmost and easternmost areas were still devoid of this invader, therefore it seems that its spread has not been finished yet. The river nerite appeared in extremely high abundances (up to 4-5000 individuals/m2) in the middle area of the lake, therefore it is likely that this species will have a significant effect on the biota of Lake Balaton, especially in the littoral zone of the lake. [ABSTRACT FROM AUTHOR]