Not just Catholics treat meat and fish differently. In the kashrut laws of Judaism, land animals and birds are considered meat. They can't be eaten together with dairy. Fish are not considered meat, which is why bagels, lox and cream cheese are kosher (and yummy). The kashrut laws of how to correctly slaughter an animal do not apply to fish either.

I still don't think anyone who eats fish is a vegetarian.
Originally Posted by geeky
Yup. That's the kind of thing I meant. It goes back to before animals were classified by an evolution-based taxonomy, and I think it might still culturally affect how some people regard fish vs. other animals (whether or not they're Catholic, Jewish, or from another group). Maybe not the best point in the world, but it's what I wanted to get across.