In this month's Gourmet Magazine, there is an article about farmed salmon that will turn you off the stuff. Even if you're a cheapskate bargain hunter like moi, after learning all the negatives I won't go near it again. Why? Health hazards, pollution, chemicals, gene pool threats, and driving fishermen out of business by depressing prices.
They don't have the article up on their Epicurious website, so You'll have to get the magazine to see it.