I agree with alot of things said here such as liscences being needed for certain fish, lfs selling tanks big enough to house fish they sell, etc. I don't agree with banning any fish though, not even large specimens such as maneating catfish. Your argument is to say "Well they don't sell great white sharks, how would you feel about that if they were to tell you how to care for it properly then sell it?". The truth is that those are two completely different issues without a comparison between the pair. Great whites rarely survive even a few years in public aquariums, the reason being that they need to move to survive. Even a public aquarium doesn't allow for the shark to be able to rest properly while continually moving as they tend to swim way out into deeper water in the wild and coast along while sleeping. Obviously catfish don't have this problem and are able to survive long periods in captivity if given the correct conditions. Not to mention that great whites are a protected species and not one that is captive bred (and I doubt they ever will be in a tank, maybe in an ocean based enclosure, but not in a tank).
I agree wholeheartedly with the advent of licenses in the fish trade, here in Oz we have to have licenses (they come in three different levels with different prices) for most native species and alot of exotics so why not with fish as well? Banning isn't a viable option I think, we get royally done over here in Oz with what fish we are allowed to keep and it often leads to a result of frustrated hobbyists while smugglers still bring in the fish and charge a fortune for them. This leads to:
a. not being able to obtain the fish at all
b. finding the fish for sale illegally and paying premium for it
c. the elevation of recessive genes in a species due to few specimens available for breeding stock
d. the afformentioned decrease of information about the species in question.
Even a huge species should be able to be obtained by a hobbyist who is able to provide the means to house and care for it, of course, exceptions in the case of endangered species should still apply and I would personally love to see all wild caught specimens stamped out in favour of captive bred ones one day (I highly doubt it will ever be completely eraticated but it is slowly being decreased which is great). I think a new way of regulating the hobby should be set in place. It should be government funded and run, either by the existing wildlife department for that country or by a completely new one (the latter would be better because it means they can pour all their available resources into it). As a hobbyist I think you should need to obtain a license to keep fish AND have to register with the said department every fish they keep (this would also help track down specimens who are on the verge of extinction in the wild and perhaps allow a hobbyist to be offered compensation for the animal so it can be bred with others of it's kind to repopulate habitats). They have this sort of registration system with cats and dogs here in Australia (not sure about anywhere else) so it could be done with fish as well.
The actual lfs should be held alot more accountable than they are too. Heavy fines should be put in place for selling to people without a license, not displaying proper names on tanks along with max sizes and for not providing detailed info about caring for the fish being sold. This info could be easily provided for little cost by placing a photocopy of the info into the bag whenever the species is sold. Granted not everybody will read this info, but these people aren't going to listen either and are already offenders right now. By providing the info it should cut back on the number of people willing to learn from making beginner mistakes.
Heavier regulation of actual fish distributers should also be set into place. Fines should be handed out for any distributer not providing the correct names for fish being shipped (this would work in co-ordination with the fines for the lfs for not displaying them, because is all honestly, it is not always the lfs fault).
By making all distributers and lfs keep a written log of all fish being sold and to who (in the case of lfs they are going to have to ask to see a fishkeeper's license before purchase anyway so the name can be obtained during this time and distributers know the names of the shops they are sending orders to) the government department would be able to keep tabs on where all the fish are going to, etc and cross reference all their databases when needed, etc.
The system itself would be self sustaining to at least a certain degree with profits received from licenses, registration, fines, etc and what it needed could be taken from government money (before you ask, they spend an awful lot on making bombs, etc. I'm sure they could syphon off some of this money, not that that would ever happen. It'd probably come from hospital and school funding like everything does, such is life I guess). The actual additional costs to lfs and distributers would be quite minimal as long as they weren't doing the wrong thing, in which case they shouldn't be in operation anyway. I know this would make an expensive hobby even more expensive for us, but considering the benefits to things like conservation, animal rights, etc I think it is a fair exchange.