Typically yes
Not sure how Alprazo feels about sand, but I try to have at least a shallow sand bed in shark and Ray tanks. The benthic sharks and especially rays hunt for their prey items by rooting around in the sand. They move the sand around to reveal any hidden worms or polychaetes, and other small inverts hidden beneath.
I think it's a matter of comfort more than anything else. I also notice with eppies and bamboos, that when piling atop each other to sleep, an instinctual moving of the sand and/or Live rock is done, to bury their heads and get "cozy".
Bare bottoms, in my experience and in talking with other local shark keepers, have lead to irritation (or just reddening) of the belly. I'm not positive about the cause behind this but it could be bacterial or bacterial slime related.
I have a 500 gallon tank with rounded sides and i wan to put a shark in it that will last its whole lifetime, what kind of shark would you buy
Welcome to the board. Not sure if you are seriously interested because these are now available through a vendor for the first time. Probably looking at $10,000 USD retail for a pair. They come only from a protected habitat so they have been probably poached. They are also temperate so they must be kept at 60F. In buying these you are likely Funding some illicit activity and poaching animals is not the biggest concern. Maybe one day South Africa will release some captive beed cats, but as I understand it, these are not. I could be completely wrong though.
Most of the cats harks that seem the most interesting and extraordinary are never brought in. On one hand, as Alprazo said, almost all except for the 3 or 4 Atelomycterus cars harks are subtropical to Coldwater animals. The other reason is many are also found in protected areas, to boot! South Africa is home to some of the most interesting smaller sharks. Same goes for Australia and PNG. It's a shame that there aren't more captive breeding projects taking place with these species but even with the hardier, tropical sharks it's not a cost effective endeavor. As a hobbiest it's fantastic to breed sharks (and fish) !