Probably no difference in Mercury content tbh. Tuna's are a large fish, so they are at the top of the food-chain in a way. They eat the smaller fish that eat smaller fish etc., and the Mercury moves up the chain as it doesn't go away. So the larger the fish, the more Mercury. Other than that, the $2 tuna at least has bigger chunks. All three of the major name-brands are owned by Asian parent companies now however... so who knows. It would seem the cheap stuff uses whatever is left over, ie tiny flakes.Honest question: what's the difference between no brand $1 tuna and the branded $2 cans? I don't eat canned tuna or any canned fish for that matter, so no idea...