All tunas are bad

http://rsbl.royalsocietypublishing.org/content/early/2010/04/13/rsbl.2010.0156.full

Too much mercury. If you must eat tuna, maybe yellowfin tunas are less dangerous to eat, because they're caught younger so they have accumulated less mercury in their bodies. But then do you eat more of them to satisfy your appetite? If you do, the same amount of harm is done. Just avoid tunas.