Underwater illusion

I photographed this tiger sand shark in the world class aquarium in Gatlinburg, Tennessee. The shark was positioned above me as I walked through a large Plexiglas tunnel, thus I was able to capture the ventral surface. I used a flash and, when I got home, had to clone out various reflections in the plastic. The original background was black, so to make this look more realistic, as if I were underwater, I added the background. The background image is a picture I took through a Plexiglas wall that enclosed a huge pool in Seaworld. I aimed up toward the sky, and the result is exactly what I'd see had I been scuba diving.