- In 77% of cases the introduction of nonnative fish has been correlated with the demise of native fish
The introduction—intentional or otherwise—of exotic species into freshwater ecosystems can result in localized species extinctions, altering the make-up of the ecosystem and in turn affecting other species.
The introduction of exotic species, driven largely by the rise of globalization and aquaculture, has a number of unintended consequences including outcompeting existing species for resources; predating upon them; or introducing new diseases for which existing species have no resistance.
One example of an introduced freshwater species that has had considerable and widespread impacts on local fauna is the Nile tilapia (Oreochromis niloticus). The Nile tilapia has been introduced for the purpose of human consumption in countries as diverse as Thailand, Philippines, Cote d’Ivoire, Brazil, USA and China. While providing a valuable food source for humans this has resulted in a number of localized species extinctions and is threatening the survival of some native and endemic species—in particular other Oreochromis species and haplochromine cichlid species. While the Nile tilapia has increased fish catch in some areas, in others it has had the opposite effect.