According to the results of recent research done in West Vancouver, the answer is “probably not much.”
But it depends.
There are a lot of factors that would come into play if genetically-modified salmon escaped and managed to invade BC river systems and it’s hard to anticipate them all. But DFO’s Centre for Aquatic Biotechnology Regulatory Research has been working since 2008 to learn about how genetically-modified salmon would perform in the wild, and around wild species of salmon.
The land-based facility grows coho that have been modified to grow quickly, and uses tanks constructed to simulate river and stream systems to do various experiments with the fish.
Researchers from the centre recently published their work in the Journal of Applied Ecology, and one of their major findings was that if genetically-modified coho salmon invade a freshwater system when they are young, they don’t pose any more threat to wild fish than any other fish in the system. However, if the fish are older, because they have been modified to grow quickly, they will be larger and can significantly reduce the survival and growth of the wild fish.
For the record, no one in the world is currently growing genetically-modified fish for human consumption.