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Goldfish & Koi Breeding Together: Truth or Tale?

Lindsey Stanton Profile Picture

By Lindsey Stanton

Koi + goldfish.

Can there be a compatible relationship?

Yep, there are many readers out there wondering if it is possible for them to reproduce with one another (especially if you keep the two species together).

Yes, Goldfish and Koi Can Reproduce Together!

The rumors are true: goldfish and koi may be quite different. Yet they DO have the ability to spawn with one another. If you keep them in a pond outside, you may find a bunch of these little hybrids in the fall once the fry have had time to hatch and grow.

This may seem strange, but both come from species of carp. Goldfish can also hybridize with other carp species (source). The mirror scale goldfish is a good example of this.

In fact, a quick Google search will pull up some unusual goldfish-type fish that are actually carp hybrids. These fish are pretty rare.

A few lucky individuals have seen them pop up every once in a while at their local fish store, but for the most part, they are difficult to get a hold of. Some other exotic scale types, such as leatherscale, hammerscale, and batik scaling, are also likely the result of such genetic crossing.

It would certainly be a fun experiment for a breeder to try to create this and make it widely available to those searching for more unusual scale types. The colors are usually not as vibrant on these “mutts” though, and they have a bit more of a wild-type look to them.

Of course, some people really appreciate their simple elegance.

koi fish in fresh water aquarium
Image Credit: Arunee Rodloy, Shutterstock

Hybrid Offspring Identification

The resulting hybrids from a goldfish/koi spawning are unique in these points:

  • It often has only one small pair of barbels (a koi has 2 pairs, and a goldfish has none). But sometimes it has no barbels at all.
  • It is sterile. Though anatomically intact, it cannot reproduce.
  • It is in between the size of a koi and a goldfish.
  • It usually has more scales on the lateral line than a goldfish but fewer than a koi. Most goldfish have 25-31 lateral line scales, whereas koi have between 32-41.
  • It tends to have a more rounded fin shape than even the Common goldfish.
  • Its tail is not as v-shaped as a goldfish’s – it can almost look more like a single-tailed broad-tail goldfish fin.
  • It can show sensory nubs above the eyes and nostrils (which look like little white dots in neat rows).
  • Some report a thicker caudal peduncle in their hybrids than what is typical for goldfish.

Some of these are easier to identify than others, but the barbels are usually the number one tell-tale sign that the fish is not a goldfish and not a koi. There is a myth out there that koi and goldfish hybrids are brown, and that’s how you can tell they are hybrids.

Actually, all goldfish fry are brown until they are old enough to start getting their true colors. This is usually around months 3 to 4 of the fish’s life. The color of the offspring really depends on the genetics of the parents.

Of course, other factors influence color as well, but it is rare for a goldfish to stay brown its entire life and does not characterize a hybrid, unlike the points mentioned above.

goldfish inside tank with background
Image Credit: Pixabay

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Blackout Comets: A Goldfish/Koi Mix?

Now let’s talk about the blackout comet. I have an interesting little secret for you. The black comet or “blackout comet,” as it is sometimes called, is not really a true comet. It’s in all likelihood a hybrid between a carp species (probably koi) and a goldfish.

Some rumors are that it’s a cross between a black moor and a comet. But this doesn’t seem to be the case judging from the fact that the black comets often have barbels and can grow to be quite large – larger than your average goldfish.

A true black moor/comet goldfish wouldn’t be able to grow past 12″ at most (and that’s really pushing it, most would probably only get around 5-8 inches). These guys can clock in around 20 inches full-grown.

This is still smaller than the size of a koi, though (which would make sense if it is a hybrid between the two). Black is a very unstable color in goldfish. It’s hard to get one that actually will remain black its entire life, even with black moors. The black often changes to orange as the fish ages.

But these blackout comets have no problem retaining their deep, strong, velvety black color their whole lives.

As far as personality goes, reports have it that these are very active fish with fun personalities. Some even like to stick their mouths out of the water when you come near them in an attempt to beg for food.

This, as well as the large size these fish can grow to, is probably the reason these are more commonly kept in ponds. They may actually have an extended lifespan due to the koi being able to live such a long time.

Information about these fish is still limited, and much is based on speculation. Where do you find these fish? It’s not easy to find them for sale, but if you know where to look, you’re in business.

Dandy Orandas has had some large ones up for auction in the past (though not very often, as far as I know). This seller supplies a group of young blackout comets shipped right to your door.

They may start out small, but give them a year or so with good food and water, and you can end up with a fish more than triple the size!


I hope you enjoyed this post that branched out a bit from the norm. Did you learn something new? Have you ever had your koi fish breed with your goldies?

If so, I’d love to hear your story in the comments below. Thanks for reading!

See also:

Featured Image Credit: JuanCarlosPalauDiaz, Shutterstock

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