
Yep, well apparently fish are exempt from pretty much all welfare laws.. the only thing we really seem concerned about in teh UK is not allowing people to bring in certain species which, if released into our waters could be very dangerous to our native fish..
Otherwise... have at fishies and do your worst - buy an arowana for your home tank, regardless of the fact they grow to 3 or 4 feet long... or a pacu, they make over 2ft long.. but you can buy one from your local fish store for a few quid.... or piranha.. a schooling species mostly (there are some that are loners), preferring to live in large groups and a very very shy fish growing to around 1ft +... not suitable for the average home tank yet you can pick as many as you like up from most tropical fish shops with no questions asked...
When there are no penalties for trying to house an animal that needs to have 240gallons MINIMUM, in a 50gallon tank... is it surprising the lowly goldfish is not regarded worthy of some welfare rights?