The introduction of alien fish species in wetland ecosystems could have a great impact on freshwater communities
and ecological processes. Despite fish introduction has been noticed as one of the principal cause of freshwater
extinctions, ecosystem processes alteration, and change in aquatic community assemblage, very few data about
impact on freshwater reptiles are available. As study model we used two neighbour sub-populations of the endangered
Sicilian pond turtle, Emys trinacris, inhabiting two small, close each other and very similar lakes, except for the presence
of allocthonous fish, Cyprinus carpio and Gambusia hoolbroki in one of the two. The multi-year study allowed
highlighting significant differences in abundance, growth and reproductive output between the two freshwater turtle
sub-populations, suggesting their influence on phenotypic plasticity of the studied population. These results are
discussed in the light of previous evidence about the impact of these alien species on abundance and assemblage of
the invertebrate community with an evident impact on niche width, diet composition and therefore energy intake by
Emys trinacris. These data may provide important information to address management strategies and conservation
actions of small wetland areas inhabited by pond turtles, pointing out a threats never highlighted up to now
