Work by Russia researcher Andrey Reshetnikov has shown that an invasive fish - the rotan, Perccottus glenii - can severely affect European amphibian populations. Rotan effectively deplete amphibian larvae in their breeding ponds, except for the noxious common toad (Bufo bufo).
One of the biggest concerns is its effect on great crested newt (Triturus cristatus) breeding sites. Reshetnikov's research in Moscow Province has shown that rotan invasion since 1950 has dramatically affected GCN metapopulations, resulting in a drastic reduction in available breeding sites.
His research is summarised in the latest issue of Froglog, the magazine of the IUCN Amphibian Specialists Group: http://www.amphibians.org/wp-content/uploads/2012/10/FrogLog104.pdf
Rotan, an alien species originating in East Asia, is widely established across Eastern Europe and West Asia. Research by Reshetnikov and others suggests that rotan have the potential to expand into other areas of northern Europe and North America, limited only by climatic factors.