Quoting Jessica Lea Bell:" I have been craving canned albacore tuna like crazy.... i have been limiting myself to 1 small can a week, does anyone know how much is too much?"
An article on Parents.com says:* Eat up to 12 ounces a week of canned light tuna and other low-mercury fish, such as salmon, shrimp, catfish, pollock, and fish sticks.
* Eat up to 6 ounces of fresh or canned albacore (white) tuna. They have more mercury than light tuna.
Here's the link if you want to read the whole thing http://www.parents.com/pregnancy/my-body/nutrition/is-tuna-safe-during-pregnancy/