How/why did this fish change colour so dramatically?


Last summer I was putting together a biotope aquarium, using all native species of fish and plants collected from local water sources (with permission). Never got finished so all fish were released with the exception of one baby carp that was about 2 inches long at the time. Its colour up until about a month ago was a dark gray (almost black) along the spine (blended very well with dark bottom), and a beautiful metalic silver along its sides. In other words, a very fishy looking fish.

About a month ago it started loosing colour. At first I thought it was a disease, but it started getting yellow. This continued up until the present day where it is now a VERY bright yellow-orange with black patches. Almost as if it were a goldfish.
Now I understand that some people have released goldfish into the wild, but Im very sure this isnt a wild variety. For one, it was too silver, and for another, it was too big to be a juvenile goldfish when captured.
Can anyone suggest how/why this thing changed colour? Is it even a carp? (the shape is consistent).
It has been kept this whole time with 2 mature goldfish, and is fed flake food.

Have read at several sites that koi (decorative carp - not goldfish) change color as they age, with each one having a peak year for the color type that they are. Have also heard that environment affects the color. Haven’t heard of such a big shift, though. You might want to google some more with words like koi juvenile color development. . . or some such.

You have just described the classic coming-of-age color change for common pet-store-type goldfish. I’ve certainly kept enough feeder goldfish alive in tanks for various reasons over the years to recognize it. Juvenile goldfish quite definitely always start out blackish/brownish/grayish and then change into gold. And 1-1/2 to 2 inches long is about the size they do this.

I’ve got news for you: there are goldfish–real pet-store-type goldfish–happily breeding wherever it was that you collected your “native biotope” species. They’re basically carp, after all, and they’re quite tough, and yes, after many years of people releasing unwanted pets into water supplies, there are well-established populations of real pet-store-type golden goldfish living and breeding in many neighborhood lakes and ponds. (The term for this is “feral”, not “wild”, so technically you’re right–it’s not a “wild” fish.)

So what you had was probably a juvenile goldfish. Or possibly koi, except that koi aren’t as tough as goldfish and don’t normally go “feral” and breed as successfully in the “wild”.

And, er, you are aware that carp are not a native North American species?


yah I know that carp were imported, but as far as Ive read so were all the sunfish varieties (or pretty much all of em anyway)
and thats pretty much the only two fish varieties that live near me that Id feel comfortable taking. (Actually Im pretty certain that at least one of the water plants Id planned on using was an introduced variety too… hmmm)
Im not sure it is a goldfish though. I mean, Ive seen what ferral goldfish look like, and this didnt foot the bill. All the examples Id seen were more “brownish coppery” than silver. Definitely gonna have someone take a close look now.
Thanks people.

There’s a simple way to tell a common carp Cyprinus carpio:

from a goldfish Carassius auratus:

Just look for barbels. Carp have them, goldfish don’t. Barbels are the little “whiskers” that appear on either side of the mouth. (Like in a catfish).

It’d be great if you’d post a pic somewhere.

Not sure what you mean by this:

What sunfish varieties are you talking about that are imported? Both black and white crappies and all the various sorts of bluegill/pumpkinseed sunfish are all native to North America.


Duck Duck, they are native to North America, but not this particular part of it. That is to say that a lot of the sunfish varieties were “brought north” in one way or another from the US (I live in Ontario).
In the link you provided under Bluegills, for example, says that bluegills were introduced into Canada prior to the 1950s.
The book Im remembering had more detail, and (Im doing this from memory, so Im probably wrong) I seem to remember that there was only one specific sunfish that was native to Ontario.

Well Spank me with a haddock. Finally managed to get a hold of someone who knows and its a goldfish after all. Huh… Well Now I know where to get free goldfish. Yay.

Oh, “On-TAR-io”, that explains it… :smiley:

Well, good luck with the goldfish. You’ll no doubt be pleased to know that since it was born and raised in the wild, it will not expect you to provide a bubbling deep-sea diver for its tank. :smiley:

But it would be SO much happier if you did.