If you eat fish then you aren't a vegetarian - it's as simple as that! I'm a vegetarian and it pisses me off when I say so, and the next question is "do you eat fish?" Er, no, because I already said that I'm VEGETARIAN. It's just lazy and it causes confusion for actual vegetarians.
Now I appreciate that the term pescetarian is a bit of a clunky term that is unlikely to be used. But it IS the correct name for the fish eating brigade.