Ecological impact of alien marine fishes: insights from freshwater systems based on a comparative review

We review the literature of marine non-indigenous fishes (NIF) in order to summarize information on their ecological impacts and to compare successful invading freshwater fishes with those in marine habitats. An increasing number of marine NIF have been observed colonizing new areas through a suite of different pathways (the main ones being inter-oceanic canals, shipping, aquaculture, and aquarium release). Ecological impacts of marine NIF have been verified for only a few of these species. These impacts can be categorized as (i) an alteration of habitat or food webs; (ii) competition with natives; (iii) predation on natives; (iv) vectoring parasites or pathogens; or (v) genetic impacts on native species. The few marine NIF with known impacts contrasts sharply with freshwater NIF taxa, for which negative ecological impacts have been widely identified. The literature review comparing freshwater and marine NIF does not reveal different species traits to explain the higher impact of freshwater NIF. We discuss a suite of ecological factors that may explain these differences. One non-ecological factor contributing to the perceived higher impact in freshwater may be the lower level of ecological knowledge in marine systems due to overall less research efforts and technical and financial challenges imposed by marine research.