Haha nice catch. I missed it originally thinking it would just be more marketing crap. So, they probably just moved it before detonating. Not sadistic bastards after all.
I know... My original reply mentioned two scenarios with one having replacement fish. Then, I thought people would think I'm overly paranoid or negative. I just couldn't help wonder if they'd blow the fish for fun then avoid liability with similar looking ones. Then, I edited the comment for sake of presumption of innocence.
But, yeah, I hear you... Great movie as well. One of few that brings my favorite mad scientist into eye of mainstream audience as well. I doubt I must name him. :)
EDIT to add: I'm guessing you think the geeks were too sadistic to pass up the opportunity, eh?