I'm open to doing anything that would be required for me to do for our own kids. If they require me to have a license to have a child then I would gladly accept being licensed to own a fish, birds, reptiles, cat, dog, horse, house, car, garage, play-do, hair products, food, utensils, etc.
In reality the fish owner's misunderstanding is a failure on the fish sellers part. It would be easier, however more expensive to the buyers, to monitor the sellers and require seller to refuse sales to people who are not equipped to take care of their purchases.
David