canned tuna is high in mercury. I'm talking about sashimi tuna if you could get your hands on some if you have a local fish market.
You don't *need* tuna or egg yolks -- i think people can do well without them, but i'm just telling you what i use for my personal diet.
Yes, the best source for your eggs are local sources - a farm that lets its chicken live and eat in its natural environment. Ofcourse, not everyone could get their hands on that. I have done quite well with eating raw egg yolks even if the source isn't thee very best as described. Egg yolks contain a wide spectrum of nutrition and contains good cholesterol -- Egg yolk is like brain food. However, the case you described about it being raised in its unnatural source, that can cause some unwanted substance in the egg yolk such as damaged (bad) cholesterol. I think the key is moderation. Once you have everything clean inside you can start adding the benefits of egg yolk to your diet -- your body can handle and i believe benefit from at least two egg yolks a day. Raw egg yolks are better than cooked eggs. Just don't eat the egg white raw under any circumstance!