...This is propaganda at its best. All comedic value aside, calling a fish a "sea kitten" is just stupid. People eat house cats too in some parts of the world, and although PETA's intentions of making people think twice about eating "normal" meats is one thing, their Western-centricness is really stupid. And not to mention their tactics, but that goes without saying.
It's true that fish have feelings and like to be petted (I've petted fish before and hand-fed them pellets (they were big pond fish btw) ). But naming them sea kittens? That's just stupid and I don't think it'll help. It'll just be annoying for people to have to instead say fish they have to say sea kittens. I like calling fish fish, its a cool name!