A vegetarian who eats fish is no problem at all. Impossible for the army, because fish is so finicky, but in terms of nutrition ANYBODY could rock a vegetarian + fish diet.

This is, of course, because fish is just a specific kind of meat, so nutritionally it's not vegetarian in the slightest.

For years I was a vegetarian + fish guy. I hate pork, my family boycotts lamb, and I didn't have a taste for beef. Nowadays I eat the token hamburger every few weeks, because I've noticed I feel a lot better for it.