I believe that some fish oils are not very pure at all. Look for "molecularly distilled" on the label. Barry Sears discusses qualities of fish oils in his book "The Omega 3 Zone," a follow up to his other Zone Diet books.
I take Carlson's lemon flavored cod liver oil, very pure and rich in omega 3's plus, of course, Vitamin D, not available in "fish oil." I need Vitamin D year round because I live so far north, sunshine rarely touches my skin. Some experts believe that SAD (seasonal affective disorder AKA feeling gloomy and depressed all winter) can be alleviated by Vitamin D, and in fact, lack thereof may well cause or at least contribute to SAD.
is there a holistic/alternative med ping list?