Shark Reef Aquarium is a beautifully constructed Aquarium in the very back of Mandalay Bay (past the Convention Center).
I brought the kids here for a break from the heat and the crowded pool. They had a great time and loved the Shark Tank. The aquarium is very small, I recommend taking your time and reading each plaque and checking out each tank. By the time you get to the Shark Tank, you are about 20 feet from the exit. We used MyVegas Rewards, so the tickets were free. I don't think it would have been worth the $20 ticket charge per person. While the Aquarium is beautiful, it's very small. I would have liked an activity for the kids somewhere in the middle so that they would have spent more time in there.