Hi-

I am going to graduate soon with my biology degree and have done much research on this subject. Alice is right. Just like the mercury builds up in the fish's body it also builds up over time. There is an accumulative effect. Right now you may not have any side effects, but if you continue eating tuna at the rate you are ten or twenty years from now you could be facing some serious health risks. Not to mention if you are a woman and plan on having children one day there could be some problems. Good luck on finding an alternative — maybe try chicken :)