The characteristics of invasive fishes:: what has been learned so far?

Invasive species are increasingly recognized as one of the main threats to biodiversity and both an urgent need and a unique tool for ecological research. Although attempts to identify future invasive species are not new to ecology, rigorous quantitative analyses emanate mostly from the last decade. In 2001, quantitative studies dealing with the distinguishing ecological features of invasive species were reviewed but no papers on fish species were identified. Subsequently, several quantitative studies have addressed this issue for freshwater fishes, including those that have focused on California, Colorado, the Great Lakes of North America and the Iberian Peninsula. In the present paper, 12 such studies are reviewed and compared with regard to their conclusions and methodology. The issues of different invasion stages and comparison strategies, propagule pressure, information-theoretic analyses v. sequential techniques, use of phylogenetic comparative methods and spatial scale are discussed. Non-native fish transport and release are the least investigated although taxonomy and human interests seem key in these first initial stages. Establishment success, which has received more study, seems more multi-factorial, context-dependent and more mediated by species-specific life-history traits. The dispersal and impact phases are less understood, although the comparison of traits (and taxonomy) between native and invasive species and particularly its variability holds promise. The lack of data on propagule pressure and the use of sequential techniques for observational data sets with many intercorrelated variables could affect the conclusions of previous studies. Research on the dispersal, impact and particularly transport and introduction phases should be prioritized rather than establishment. All the studies identified were at temperate latitudes in the northern hemisphere; studies in other regions and comparison of different regions and multiple scales are lacking. (c) 2007 The Author Journal compilation (c) 2007 The Fisheries Society of the British Isles.