Do vegetarians eat tuna

No. * Most vegetarians do not eat "meat," which, by definition, is the flesh of another creature (i.e., meat does not refer solely to cows). Thus, virtually any seafood (e.g., fish, mollusks, etc.) that could reasonably be considered as having flesh would not be eaten by "true" vegetarians.

However, as with anything else, individuals have the right to choose to eat whatever they wish, and, as such, there are some flesh-eaters who consider themselves "vegetarians," though others might not. Refer to the link, below, for more information.

* Vegetarians don't eat any fish.