I was thinking about eating a few cans of tuna and remembered that Tuna is high in mercury and was wondering how many people are worried about ingesting mercury. Many sources suggest you eat no more than 2-3 servings per month. people in china who eat dolphins for example which have extremely high amounts of mercury have died from it.
http://www.nrdc.org/health/effects/mercury/tuna.asp (serving size chart using weight as variable for safe amount to eat )
just a few of thousands of pages about it