There is a largish (free) display in Mandalay Bay's registration area.
The Shark Reef was a major disappointment to me, for the price. The enormous tank displaying jelly fish is amazing, although it seems overcrowded. Lit by actinics, the jellies glow blue. It was my favorite bit.
Overall, it is a lot of water, pretty heavily stocked with large species.
I don't know what I was expecting, but I would personally have been happier if there was a brightly-lit coral display or two. The fibreglass reproductions don't excite me.
Here's a link to some clues you can use:
http://www.inetours.com/Las_Vegas/pa..._exhibits.html The behind-the-scenes look at the Ceasar's Atlantis aquarium (my favourite LV tank) is something I didn't know about last time I was down, but I'll be doing it next time for sure.
Matt