From Rutgers: another genetically modified species effects on ecosystem. Reads:

A new study carried out by a team of researchers from Canada has revealed the link between the introduction of GM (genetically modified) fishes into the wild, and damages to the ecosystem.

GM salmons, in particular, when let out into the wild, tend to mate with the closely-related brown trout species, which then produce a hybrid fish. While the GM salmon grow faster than a normal salmon would, its hybrid offspring grows even faster, thereby out-competing the existing species for their food.

http://www.itechpost.com/articles/9928/20130529/gm-salmons-hybrid-offspring-harm-ecosystem-study.htm