As I really want to understand all this, I ordered Sears' "The Inflamation Zone" yesterday (for my e-reader).

Although not an easy read - it could do with some editing - I already found very valuable information about fish oils. (and other supplements)

There's a Canadian website called http://www.ifosprogram.com/consumer-reports.aspx, where you can find tests of a lot of brands/batches. It's not a commercial organization, and they test on both quality of DHA/EPA and contaminants.

I was amazed at the high dose he recommends (to complement his diet), and will read a bit more before I commit to it. Still, all very interesting information.