The glass-bottomed boat gave us a perfect view of the marine life. Our tour guide told us that the sharks feel disinclined to eat the other fish for three reasons: firstly, the fish are very well fed and don't feel the need to hunt; secondly, sharks prefer to hunt injured or weakened prey and the Aquarium fish are generally neither; and thirdly, the tank has been cunningly stocked with fish that sharks won't usually eat anyway. FACTS, everyone!
Some sharks do need to keep in constant motion to breathe, but the lemon sharks we saw are not among them — they use a muscle to push water through a vestigial gill called the spiracle over the gills. They do not, however, have a swim bladder and cannot float if they stop moving and will come to rest on the ocean floor. This fellow obligingly took such a rest just long enough for us to snap a few shots.