Another view into the big tank at the Georgia Aquarium, shot through nearly two feet of acrylic. This manta ray has a wingspan of probably eight feet. Fully grown, their wingspans average 20 feet.
Since a few people have asked, here are a few hints for shooting through thick glass in large aquariums. First and foremost, bump up your ISO to the highest speed you can use and still get reasonable image quality. I use ISO 1600 on my Nikon D300. Shoot wide open or close to it, depending on your lens quality. What you are looking for is a combination of aperture and ISO that will get you at least a 1/60 second shutter speed. (It is, after all, hard to get a fish to stand still!) Use a wide angle lens and get as close to the glass as possible, even for close ups. (Speaking of glass, get to the aquarium when it first opens and before the glass is covered with thousands of finger and nose prints.) Turn off your flash (most aquariums don't want you to use it anyway and the reflections will usually ruin your image). If you have sufficient light, use a polarizer to reduce glare and reflections. A lot of aquariums light their tanks with a combination of natural and tungsten light so white balance can be tricky. For that reason, it is best to shoot in RAW format and adjust the white balance in post processing. Above all, be patient. Pick a good spot and wait for the fish to come to you. Finally, shoot a lot of images and expect to throw most of them away.