According to the U.S. Food and Drug Administration, fish such as tuna may be eaten raw if previously frozen, because the freezing will have killed parasites in the flesh. However, not all harmful micro-organisms are killed by freezing, which is why the FDA recommends cooking any fish.
According to the FDA, most seafood should be cooked to an internal temperature of 145 degrees Fahrenheit. The FDA notes that pregnant women, older individuals, young children and people with compromised immune systems or decreased stomach acidity should avoid raw seafood. The Natural Resources Defense Council recommends eating lower mercury fish in sushi and other raw seafood preparations. The NRDC lists albacore, bigeye, bluefin and yellowfin tuna as fish high in mercury.