1. the guys head is right on the top of the frame, which bugs me personally. One of his eyes is a little raccoon-ish. Plus, I'm not sure the ferret thing is in focus.... Maybe its blurred though? Something seems wrong. Also, is the yellow glare from the aquariums and stuff? Can you try to get rid of it?
2. This one seems underexposed and I think just barely out of focus. Also, a little deeper dof could have worked better, I think.
3. Everything is very yellow. From the lights in the tanks? I think this could be brightened up as well. The blue on the top contrasts with the snake, and I think if you cropped it out the composition would be improved anyway.
4. I think that this is the best one, but maybe also underexposed (is it my monitor?). Is there anyway you could get rid of the shine from the glass on the left side on the coral thing? I think I would have preferred deeper dof here as well.
This seems like a tricky place to take pictures. It doesnt seem very bright, and I'm thinking that the different tanks and aquariums are giving off all sorts of funny-colored light.