The biggest problem with zoos and things like that are the fences. If there was a way to find an angle that let you shoot without the fence in the way, it would (obviously) make for a much nicer shot.
Having said that, these critiques will ignore the fence issue.
#1 - I would crop this shot down a bit. A good rule of thumb is to remove anything that doesn't add to the shot. In this case, there's a lot of extra space above the Kangaroo's head that isn't helping anything. I think the placement of the animal is good, though a little more space to the left might make for a more pleasing composition.
#2 - I love this shot. It's hard for me to find anything to critique about it. I might crop down a bit, just to fill the frame with the animal a bit more, but other than that, it's a great shot. I even like the shallow DoF you achieved. Focus seems spot on, and good exposure.
#3 - This is a cute shot. I might crop away a bit from the left. Focus also seems to be off a bit, but it's hard to tell. There's a good chance your camera caught one of the chain links to focus on, and it through everything else off. Something to be aware of if you're shooting wide open, which it appears you were.
#4 - Seems to be some camera shake. I'm assuming a dark room with a lit up aquarium? These are tough shots to get, to be honest. Placement of the fish seems good.
#5 - As I've said before, I'm a sucker for dogs, and this is a cute one! The center placement isn't doing anything for me, though.
Thanks for the critiques. I hate the fencing at the zoos, they make shots so much harder to get. And this paticular zoo had two sets of fences for a lot of the animals. They had a fence then about 6 inches away they had another fence so it made shots that much harder.
I love one of the baby raccoon too, but it does seem like the focus is a bit off. And unfortunately I didn't realize until a bit later that my iso was on auto so it is a bit grainy.