New research has shown that human introduction of fish into rivers over the past 150 years have modified the average body size of fish in many areas of the world.
A study conducted by researchers from CNRS, the University of Toulouse, IRD and MNHN, as well as the University of Antwerp and University of Utrecht, shows that non-native fish are larger than native species by an average of 12 cm. This modification in the size of fish poses a serious risk in terms of the alteration of aquatic ecosystems. The results of the project are published in the April 2010 issue of Ecology Letters.
Since the Neolithic era, human beings have been transporting and introducing new species. This practice has accelerated over the past 150 years along with the development of transportation methods and international trade. The phenomenon extends to freshwater fish, several hundred species of which have been introduced throughout the world, either unintentionally or for food or recreation purposes.
By cross-referencing data on the fish present in 1,050 river basins around the world, researchers have determined that the fish species introduced by human intervention are an average of 12 cm larger than the species naturally present in these rivers, which increases the average body size of the fish in a given river by about 2 cm.
This modification affects Bergmann's empirical rule, which expresses the fact that the farther an organism lives from the equator, the greater its body mass. This principle is the result of the joint evolution of species and their environment over millions of years, and, as this research reveals, humankind seems to be in the process of altering its profile.
Beyond these historical considerations, the introduction of species whose ecological characteristics differ from those of the native species can also affect the functioning of the ecosystem. Some of the larger species widely introduced throughout the world are predators (trout, black bass, catfish, etc.) whereas others are detritus feeders or herbivorous (carp, tilapias, etc.). These ecological characteristics are likely to modify the food chain or the recycling of organic matter. Modifications in the average body size of fish observed in river basins on a global scale could thus go hand-in-hand with modifications in the functioning of aquatic ecosystems.