Hi,
I'd love to help but am unsure of what fish you mean. As I am in the UK common names of fish are unreliable in indentification situations. Do you know the Latin, or scientific name of the fish? Can you tell me if you are talking about a bottom dwelling fish, what size you think the fish will grow to, or are these the things you are trying to find out? Are you sure it is a saltwater fish?
The fish that we know here as a banded shark (prefixed by high fin) is a fresh water fish that should only really be kept as part of a serious attempt to breed them as they are endangered. They originate from China, the Yangtse River, and are not really even a tropical fish, but a temperate or cold water species.
As I say I would love to help, but as your description and mine are so, so different I think it is unlikley we are on the same species! More info please!
Even if you don't know the scientific name any thoughts or info on what you already know about them may be helpful.
Glad to see another fishy dude here, meant in the best possible way!
I fear, however, that we have so many different names for the same fish we may never be talking about the same fish! It's worth a try though and at worst will be a laugh!!