You would need a large tank – and bank balance – if you wanted to take Rocky home to keep. The whopping guppy is believed to be Britain’s biggest goldfish – weighing more than a bag of sugar or a premature baby. Rocky the red oranda is six inches long, four inches wide and weighs a staggering 2lbs 10oz.But such a big fish will cost you more than the average prize from a fairground – Rocky is worth a four figure sum. But the oddly bulbous creature is almost worth its weight in gold, as its rare size and breed makes it worth £4,500.That makes Rocky incredibly desirable among fancy goldfish collectors. The three-year-old red Oranda, is native to Japan and China, and is characterised by the prominent growth on its forehead, or ‘wen’.This can cause problems for the breed, however, as it can reduce the fish’s visibility if it grows to cover the eyes. Despite not appearing very hydrodynamic, they are powerful and strong swimmers. Rocky’s owner, Andy Green, is owner of Star Fisheries in Sutton, London which imports and sells fancy goldfish.Andy, 55, said, “It’s the largest goldfish in the UK. It’s very wide, and really heavy. Compared to a normal goldfish, Rocky is an absolute giant. She is also certainly the largest of his type ever to be imported into the UK.” He said, “She’s an incredibly strong and powerful fish. That’s where we got her name from. She came from China, and it took me six months to convince the breeder to sell her to me.”He added, “If I were to sell her, I wouldn’t accept less than £4,500.”Andy admits fancy goldfish are a weird thing to sell, but there is a strong market out there for rare and prime examples of them.He said, “Some people find them really ugly, especially the fish with bubble heads. But others absolutely love them. The goldfish all have different characters and temperaments, which makes them really interesting. Collectors will also pay big money to make sure they get prime examples of goldfish. The most expensive fish we sold was a panda oranda, which went for £6,500 two years ago. We specialise in supplying the best of the breeds to make sure people are always happy with them.”Andy has been selling goldfish for 35 years, having grown the business from his uncle’s back garden.His love for goldfish goes back even further. Andy said, “My interest in goldfish began when I won one at a fair as a 10-year-old, and carried on from there. When I was 12 I started breeding and showing them, and had great success over the years. By the time I was 20 I realised it was something I’d love to carry on doing, and so I started my own business. I was in my uncle’s back garden with just a few fish tanks, and my fascination grew from there.”Rocky is not the biggest goldfish ever recorded in the UK. A 16in-long fish, weighing 5lb, was caught in a lake in Poole, Dorset, by 16-year-old Nick Richards in 2010.It was thought the fish had been abandoned in the lake after outgrowing its tank.