Much has been written about pollution in the oceans and contaminants such as PCB's and mercury in fish. But fish high in omega 3 fatty acids provide enormous health benefits so it's worth learning more.
I'm aware of charts available online from the Monterrey Bay Aquarium on how to buy sustainable fish but it's complicated and takes time to work through. Recently I've read two articles that simplify the process.
The October/November edition of Fine Cooking chooses 5 fish that are plentiful, sustainably caught and have low levels of contaminants. Their choices: Arctic char, black cod, striped bass, Pacific halibut and Atlantic mackerel.
Cooking Light recommends albacore tuna, catfish, Pacific cod, Pacific halibut, wild Alaskan salmon, striped bass and tilapia.
Only purchase fish that has been kept on ice and has no fishy odor and plan to serve it today or tomorrow. If you don't see the kind you're looking for ask at the fish counter for their suggestions.
I serve a lot of shrimp and look for wild American shrimp or farmed shrimp for the U.S.
By selecting sustainable fish and eating it at least once a week, it's a win, win. It's good for the environment and good for your health.