I would be careful in buying any farmed salmon and now with the genetically modified frankenfish coming out that too. I think it's estimated to hit in about a year in which case f it does salmon would not be safe for consumption period once the actual salmon die off.
I say this with great disappointment and have filled petitions and blah blah about gmo foods and the salmon because it's important, but your only safe bet would be wild caught Alaskan. It's expensive fresh, so I get the canned version with skin and bones. You get omega 3 and calcium and it's 50% off. It has been my main protein source for about two years, the 14.75 oz cans. I rarely would cook it due to due danger of oxidizing the omega three, if you plan to take the skin off and eat it.
I hit it with some steam over a sauce or rice when its at the last 5 min of cooking. You don't need to worry about metals if you have Alaskan salmon.