What's the biggest animal in the aquarium?

End to end I would guess a jellyfish. By mass, I'd guess, Tuna but maybe Hammerhead Shark or Giant Turtle.

They have some pretty big sea bass, and some other good size fish, and in the bigger tank were some good size fish of all kinds

So the largest animal is the blue whale up on the ceiling, but that's probably not the answer you're looking for. As far as live animals are concerned the octopus might be the largest animal arm to arm. There is also a giant sunfish and some extremely large tuna in the deep sea area.

Sea Lion

There were no sharks when I was there...

Sea otters probbly, aside from humans.

Giant sea bass

Humans

Probably a shark of some kind or otters