Goldfish: How big do they get?!?!

Factual Questions
1

A few days ago I was looking down into the water at the entrance to the Chicago river when I saw some pretty big goldfish. They were 12"-15" easy, and bright gold in color - so I’m assuming they were goldfish. A colleague I was with saw them and remarked that goldfish size is usually limited by their tanks or bowls, and when they end up in a large body of water, they get H U G E.

:dubious: ( <— naturally skeptic of all things provided without authoritative citation thanks to the conditioning of the SDMB smiley)

OK - so:

  1. Is it possible that I saw really big ‘traditional’ goldfish?

  2. Is their size limited by the tank or bowl they’re in?

  3. Just how big will those suckers get?

2

When I was a kid I bought some ‘feeder fish’ for a nickle each, goldfish that were intended to become meals for oscars and whatnot. I had a five-gallon aquarium. Then they moved into a ten-gallon aquarium, and then a 20-gallon one. They grew slightly as they were moved into larger tanks, but not much.

Then mom put a fish pond in the back yard. Maybe 300 gallons or so. These nickle-a-piece goldfish grew to about six to eight inches long. And they started breeding.

12" to 15" is a larger goldfish than I’ve ever seen, but based on my experience with my goldfishes it sounds plausible. I’ve heard that goldfish will grow to a size sustainable by their environment. This seems to have happened with mine. No idea what the upper size limit for a goldfish it.

3

Here is the record 18.7"

4

I’ve seen those fish too and they’re enormous. I don’t know if they’re goldfish or what but I once saw one of them eat a new baby duckling! :eek:

Well, I assume it at it rather than it just being a malicious drowning.

5

They can’t grow indefinitely. There is some point at which “cube/square law” considerations will make the design not work. Even if you provide a habitat the size of Lake Superior, you aren’t going to get a fifty foot goldfish. The Wiki article says:

I would guess that the fish in the Chicago River are common carp - related to goldfish, but they get bigger. In fact, here’s a blurb about the “Chicago Carp Classic”:

http://www.carpecarpio.com/chicagocarpclassic2000.html

6

It’s probably also worth noting that people will often confuse koi with goldfish, since the koi may exhibit similar coloration. The koi is an ornamental domesticated version of the common carp, which can grow to 4 feet long. Wiki article on koi:

7

A Fish Out of Water :slight_smile: