Being pescatarian means that the only meat you eat is fish. People go pescatarian for a number of different reasons; the first of which is the fact that fish have a lot of nutrients in them, so some people who want to give up meat feel it's important to continue eating fish. Another reason might be that being pescatarian is the right balance between being vegetarian and eating meat. The next purpose I can think of for being pescatarian is that some people claim fish isn't real meat because they are cold-blooded!
So, what do I think about pescatarianism? I can see why people do it, that's for sure, but it's completely unfair on the fish! It's not their fault they're nutritious or that they are cold-blooded, so we shouldn't take advantage of that. If the only meat you ate was pork, you would feel terrible for the pig, wouldn't you? So what's different about fish?
Another argument some people use to tell themselves that it's okay to eat fish is the theory that fish cannot feel pain, but recent studies show that that isn't the case; fish feel pain just as much as we do, though in a different way!
I was vegetarian until the end of my eleventh year, when I stopped eating animal products altogether. There was no in-between for me. For meat-eaters wanting to be vegan, the step-up should be vegetarianism, not being pescatarian. We can't keep using fish as leverage: both farm animals and fish deserve- free and threat-less!