Where in the world do goldfish swim wild?
“On Golden Pond”
Common goldfish, referred to as comets, are native to China, though the comet’s ancestors were more greenish brown. Selective breeding has created the myriad colors and shapes known these days. I would suspect they have become naturalized to the US as well via the widely used method of disposal (flusssshhhhh).
Har har. Seriously, goldfish are hardy little devils. They thrive in cold water and are bottom feeders. Aren’t they carp? Aren’t they related to koi?
I don’t have an answer, just more stupid questions. But I think they are carp, and they’ve probably been selectively bred to be pretty little fishies, much like we bred dogs and cats to look nothing like their anestors. But, unlike some domesticated cats and dogs, I think goldfish could survive in the wild because they do like cold, they do eat crap, and people do keep them outside in ponds.
Maybe Asia? (Remembering The Simpsons’ Mr. Burns’ grandfather mocking the idea of the Japanese devouring us economically because they’re “sandal-wearing goldfish tenders.”)
“I hope life isn’t a big joke, because I don’t get it,” Jack Handy
Oops, beat me to it, sly, and with a much smarter answer. Thanks 
(But don’t forget goldfish naturally prefer cold water, and thrive in outdoor goldfish ponds… we used to keep goldfish in the tub we watered the cows from, and they survived even when the tub froze over. Don’t know what the cows thought about drinking fish poo, though, but then they drank out of the creek, too, and I’m sure it had much more fish poo in it.)
“I hope life isn’t a big joke, because I don’t get it,” Jack Handy
To the best of my knowledge, goldfish thrive about anywhere. I had some in college after an art project I did (don’t ask) so I gave them a good home in a cheap aquarium. They were doing okay until I had to go home for 3 weeks for winter break and just left them to fend for themselves. No feeding, no decent filtration for three weeks and when I returned the water was so thick with green you couldn’t see halfway through it, yet the goldfish were bigger than ever and happy as you could reasonably expect a goldfish to be. Eventually, at about 5" each (they were bought as tiny feeder fish for about 10¢ each) I released them at the year’s end into a large water retention pond where I have no doubts they happily live today with their little goldfish children.
“I guess it is possible for one person to make a difference, although most of the time they probably shouldn’t.”
Goldfish are mutated carp, and koi are mutated goldfish.
Goldfish will definitely thrive in the wild – under almost any conditions. At my alma mater we had a (very polluted) pond where students would release their goldfish when they moved out. Not only did they live, they grew to at least a foot in length.
I’ve read that the colors we usually associate with goldfish take a lot of selective breeding (and probably an environment with few predators). After a few generations in the wild, the bright colors will disappear, and you’ll be left with a bunch of gray-brown great-grandfish.
Goldfish are the results of selectively breeding the wild form, and yes, they are in the carp family. As others have said, the original form is a green brown (i’ve read its more of an olive color). If you release goldfish into the wild they will revert back to that color, and so will their children. Koi are a different species, but related to goldfish. Goldfish get up to about 1 foot (my parents had a gold fish that got that big, and they renamed it “Moby dick”). Koi can reach three feet and i think live for a few hundred years! The funny thing about koi is, if they “hear” running water near their ponds, they’ll try to jump out of their pools. I have heard them referred to as “Chinas answer to Salmon”. In fact, they do fight their way upstream, over waterfalls to breed, like salmon do.
Growing up in NH, I lived on an island that had been formed by an oxbow - river changed course and left a horseshoe-shaped pond (oddly enough called Horseshoe Pond. Oh those artistic creative NH types!).
On the mainland side was a cluster of summer cottages and I’m sure the summer complaints got goldfish to keep while they were on vacation; these fish were dumped into the pond at summer’s end. At least that’s the conjecture because every year us kids saw at least one hunter’s-orange colored carp that was at least a foot long. So I guess the answer to the original question is they swim wild wherever they get put/damn well want to.
All the goldfish books I read pretty much agreed that they came from Asian carp (which were called koi to begin with) that got domesticated for decorative purposes. Chickens also apparently came from Asia (via the Wild Asian Jungle Fowl). So if goldfish and chickens were both given to the world from Asia, that leaves one question: do goldfish and koi taste like chicken? 
Cave Diem! Carpe Canem!