A great overview of the history of keeping goldfish along with interesting facts.  
 
About four million households in the UK own fish, which equates to roughly 14% of the population, according to the Ornamental Aquatic Trade Association. Attractive, colourful, easy on the eye and calming, ornamental fish offer a low maintenance alternative to cats and dogs and even spare your furniture.
 
Curious Question: Do goldfish really have a three-second memory? - Country Life