"...one shouldnt Supplement with Selenium shen having Silver Fillings."
Personally, I regard that as nonsense. The body needs selenium for many of its detoxification enzymes, and it would make no sense whatsoever, to say that because a person has a toxin in their mouth, that they should not ingest the key trace element necessary for removal of that toxin.
Tuna typically contains about a half of a part per million by weight of mercury, and it would need to be an enormous-sized can of tuna to contain as much mercury as 10 or 15 fillings.