Parasites of fish and other aquatic organisms in the Anthropocene.

The Anthropocene is the most recent period in Earth's history and is characterized by humankind-driven alterations to all ecosystems. Climate change, pollution, overfishing, invasive species and habitat degradation continue to reshape aquatic ecosystems, and like all living organisms in our changing world, parasites are likely to be affected at different levels. This Collection features research and review papers on some of these topics: parasites co-introduced with their fish hosts illustrate that biological invasions must be studied case-by-case, as some fish hosts lose their parasites upon translocation (enemy release), some pass them on to the invaded ecosystems (overspill) and some acquire -and sometimes amplify- native parasites (spillback), regardless of the time frame, as illustrated in studies of parasites co-introduced from 150 to 15 years ago. Biological information is a powerful tool to predict and prevent the spread of invasive/pathogenic species, and while this Collection provides baseline data for several introduced parasites, it also features practical proposals to control pathogenic/zoonotic species. Climate change and habitat alterations also exert a powerful influence on parasite populations - which likewise, must be studied individually, as some species decline and/or modify their distribution markedly (leading to hybridization and potentially speciation of previously separated taxa), while others benefit from the modified environment, are able to invade new hosts and/or become more infective or pathogenic. Parasites play different ecosystemic roles and are finely-tuned bioindicators of anthropogenic impact in freshwater ecosystems, and this Collection highlights the notion that they should be integrated in public health and conservation initiatives.