My understanding is that you need to cook it almost immediately. Sharks have a primitive waste removal system and the meat goes bad quickly. That aside, cubed and kabobed shark is mighty tasty. Sort of like tuna.
http://www.ocean.udel.edu/mas/seafood... Here's a link for the ammonia issue. Appears that if the shark is bled properly ammonia shouldn't be a problem. I have only eaten shark deep fried in fish tacos.