Welcome to the board "capt rick". You'll need to be a little more specific in your question. Do you mean dive for your own fish and then keep them alive???
Some people do it and it can be done.
I go snorkeling around a local reef where I see Tangs, damsels, bleenies, and many other fish and inverts commenly sold in a LFS.
I have never tried catching any though but have seen many people there with nets.
