Domesticated salmon, after several generations, are fat, listless things that are good at putting on weight, not swimming up fast-moving rivers. When they get into a river and breed with wild fish, they can damage the wild fish's prospects of surviving to reproduce.
Charles Clover (2008). “The End of the Line: How Overfishing is Changing the World and what We Eat”, p.312, Univ of California Press
