Another really useful thingy from the MBA is this pocket sustainable seafood guide. In different areas, different types of seafood are better choices for you and for ocean ecology. The seafood guide helps with ordering at restaurants, and shopping for seafood at home. (A basic rule is to stick to smaller fish. They reproduce more often, and may take on fewer contaminants like heavy metals.)
If you're traveling, it can help you out by telling you what local names seafood you already know and like may be sold under.