I spent a long weekend down in Atlanta for a belated birthday celebration (it's a round number, that's all you need to know), and one of our activities was to visit the Georgia Aquarium. Their ocean tank is really impressive, with a sixty foot long viewing window made of acrylic two feet thick. I managed to snag a couple of pictures with my cell phone camera: not the best tool, but you work with what you have.
The whale shark in the foreground is actually one of their young males, coming in at only fifteen feet in length, if I recall correctly. One of the females -- over twenty feet long -- is following in the background. The aquarium staff say they're hoping their whale sharks will grow to thirty or forty feet in length and even breed, if they're really lucky.
For a little sense of scale, here's Fjorleif standing in front of the window. The big fish swimming by her is a grouper. According to the staff, the acrylic window does not magnify what you see through it, and the keep a block of the acrylic off to the side so you can verify that for yourself.