I feel a little dorky suggesting this... but have you thought about trying a substitute? There's a vegetarian "tuna alternative" called Tuno that we buy every once in a while, and we really like it. http://www.veganessentials.com/catal...lternative.htm
I eat fish occasionally (my bf'ed kids have had allergy problems, and when I've had to eliminate a lot of foods, I'd eat some fish, in part so I had *something* to eat). I agree with the pp that there are other, safer fish to eat (if you do a search here at MDC, you'll come up with some threads with some valuable links and info).
When I have a craving for something that I shouldn't eat or would rather not eat (or want to eat less of), I think about what it is about the food in question that is so desirable. Often, I can think of something else to eat instead. I'd admit that for *me*, the celery and mayo in tuna salad are a big attraction, so if I get the Tuno and Nayonnaise and the celery, I'm fine. (But I may just be a nut.)
The downside of Tuno is that it's definitely more pricey than tuna.
(If you got a chuckle out of Tuno, check out my favorite "analog"... the Veat faux salmon fillet... http://www.veat.com/products.html
and scroll to the bottom :LOL )