If you're going to base your diet on compassion, the question should be "is what I'm about to eat capable of suffering?". If it is, you don't eat it. That excludes all vertebrates, and probably dairy products as well, but probably not insects or their products, such as honey (I wouldn't eat insects, but that's from squeamishness. Actually, our modern squeamishness asbout eating insects is a relatively modern, Western idea: other cultures, past and present, think nothing of it.) I doubt if bivalves can suffer, so they should be ok.