Wild vs. Farm Raised Salmon | What is healthier? | Is Farmed or Wild Salmon better?
Sea lice is a common (potentially fatal) problem for farmed salmon. Whenever this problem is detected, farms add pesticide (emamectin benzoate) to the feed.
Farmed fish are also fatter because they are "marine couch potatoes."
Too, having more fat means they likely store more toxins like PCBs. For more information on that, use the link above.