I know, I know, labels are meaningless. We're all different, don't try to pigeonhole us. But labels are handy sometimes, when used correctly. So here goes:
Vegetarians do not eat the flesh of any animal, be it mammal, bird, or fish. They may or may not, depending on personal preference, eat dairy and/or eggs. Vegans are strict vegetarians, rejecting all animal products, including honey, leather, etc. (And I respect them enormously for their self-discipline.)
A fish is an animal. Remember Grade 8 biology? The plant kingdom and the animal kingdom? Well, fish are firmly planted (so to speak) in the ANIMAL kingdom. Therefore, vegetarians don't eat fish!
So don't call yourself a vegetarian if you eat fish!! They're animals too! Just because they're not MAMMALS or BIRDS doesn't mean they're plant life. And if someone advised that he/she is vegetarian, DON'T ask them, "But you eat fish, right?"
And calling yourself "pesco-tarian" is just silly. Bloody labels.