I think that a 6 ounce serving of tuna is considered safe -- the only concern I'd have from the bagel store is for portion size.
I have eaten tuna here and there - I just ate it in moderation. From what I read one can a week is safe.
I have eaten tuna fish and like the other girls said, as long as you limit yourself to one can a week you should be fine. A sandwich from the bagel store might be a little more than 6oz of tuna, but I wouldn't stress that much about it if you haven't eaten any other fish this week. And if you have, then just scrap a little off the sandwich.
I have it every once in a while... I think you just cant have it every day.
I eat it at least once a week
