The rampant introduction of non-native freshwater fish has led to a significant change in the average body size of freshwater fish assemblages around the world, according to research published in the April 2010 issue of the journal Ecology Letters.
Simon Blanchet and coauthors statistically analysed data from more than 1050 river systems around the world, and found that introduced fish species are an average of 12cm larger than species naturally present in these rivers.
This has the effect of increasing the average size of the fish fauna in the river systems analysed by about 2cm. This change is considered remarkable, since beings have facilitated the establishment of a few selected species (about 0.04% of the worldwide species pool) in a very narrow span of time (hundreds of years).
The alteration of the body size structure of most freshwater fish assemblages worldwide by human beings may affect the way ecosystems function, according to the authors. The biological attributes of non-native fishes can affect the function of recipient ecosystems either through predation, carbon storage, nutrient recycling or bioturbation.
For more information, see the paper: Blanchet, S, G Grenouillet, O Beauchard, PA Tedesco, F Leprieur, HH Dürr, F Busson, T Oberdorff and S Brosse (2010) Non-native species disrupt the worldwide patterns of freshwater fish body size: implications for Bergmann's rule. Ecology Letters 13, pp. 421–431.