That would be pretty sad...the baby probably won't be able to turn around and will most likely develop deformities in a 20gal. :headshake2:
Joking aside, I don't agree with everyone about completely removing potentially large fish from LFSs as it will make things much harder for aquarists who are actually able to house these wonderful fish.
I like wataugachicken's suggestions for the most part. Adding a higher tax will probably work for most of the more inexpensive larger fish, however it probably won't work for more expensive fish like arowana. From what I've seen, most people who want one normally don't hesitate to spend 40-80 dollars for a juvenile specimen depending on the type of Aro, even if they are completely new to the hobby. That is easily 10 times the price of an average fish and I don't think a few more dollars will make a difference. I do, however, think that holding the LFSs responsible for taking back the fish is a great idea. LFSs will be more selective of their sales or risk losing money from taking care of a large fish that they have to house and provide food for. Even if they resell the fish, they will likely spend 3 times as much as they made from simply feeding the large fish.
But I dunno, there's really no good replacement for knowledge. For the most part, we have to get society to recognize fish as living animals rather than disposable decorations. Only then will these regulations ever be enacted.