I get this question a lot:
“Is my fish a koi or a goldfish?”
It’s something I’ve wanted to make a detailed post on for some time…
… And today is the day 🙂
Now:
It is hard to confuse fancy goldfish with koi due to their drastically different body shapes.
Slim-bodied fish (i.e. Commons, Comets, Shubunkins) might be a bit more tricky.
That’s why I’ve put together this guide to koi and goldfish differences.
Some of these methods are more reliable than others.
All combined, it should help to paint the picture of the fish you are trying to identify.
I hope it helps the next time you’re looking in your pond!
1. Presence of a Pair of Barbels vs. None
This is probably the fastest and easiest way to tell the difference between a goldfish and a koi.
Check the mouth for two pairs of short pointy “whiskers” on each side (one pair will be noticeably larger than the other).
If the fish has them, it’s a definitely a koi.
If not, it’s a goldfish.
What are these little barbels anyway?
Some speculate that they help the fish navigate through and orient itself in turbid waters.
Kind of like how an insect or snail uses its antennae.
They give the koi a very unique look.
Related Post: Goldfish Vs. Koi
2. Attached Dorsal Fin vs. Dettached Dorsal Fin
Now you can look at the end of the dorsal fin closest to the tail.
Does it lead straight down to the body?
Or does it kind of go under and separate a bit first before joining the fish’s back?
Attached = Koi.
Detached = Goldfish.
This method might be a bit tricky to use until you practice it enough.
3. Flat Under Jaw vs. Rounded Under Jaw
There’s something about the head shape of a koi that is quite distinct from a goldfish’s head.
One big reason for that is the flat jaw along the underside of the koi’s head.
A goldfish has more of a rounder curve below the chin before the head joins to the body.
Why this is?
I have no idea 🙂
It seems it is just another thing that is unique to each species and gives them their own special appearance.
4. More Body Weight in Front of Dorsal Fin vs. More Body Weight Behind it
Look:
Koi have a larger percentage of their muscle mass in front of the leading edge of their dorsal fins.
For most goldfish on the other hand…
… it’s more evenly distributed along the body before and behind.
Some older, well-fed goldfish can get quite robust on the area behind their heads between their heads and where their dorsal fins start.
But most of them (the slim-bodied ones anyway) are pretty tube-shaped.
Typically:
Koi have more of their bulk nearer to their head.
5. Presence of Fancy Features (for Goldfish)
This isn’t always reliable depending on the variety of goldfish you are looking at.
But one thing that makes some goldfish different than koi is that they can have double tail fins.
This can indicate the fish is another type of pond goldfish like a Wakin, Fantail or Jikin.
Other fancy features goldfish have that koi don’t include:
- Pom poms
- Bubble eyes
- Telescope eyes
- No dorsal fins
- Short round body
- Wens
Although Koi varieties such as the longfin or “butterfly koi” might have extremely long, exaggerated fins, this is not considered a fancy feature like those of goldfish.
6. Certain Colors and Color Patterns
Koi and goldfish can share some similar coloring, so this isn’t always the best method for distinguishing between them.
That said:
Sometimes it can come in handy.
Many goldfish kept in ponds are usually solid orange, white or orange and white (also known as sarasa).
The Shubunkin goldfish has the body shape of a Comet with longer fins, but is a calico coloration of white, black and orange.
Koi have a huge variety of color patterns and scale types, many of which are not seen in goldfish.
Some of them are quite incredible!
It is the coloration of a koi that often determines its value.
The same is true of the more expensive goldfish breeds on the market.
The more rare the color, the higher the price.
See also: Koi Fish For Sale
7. Much Larger Size Potential vs. Not as Large
Your fish have to be adults to use this method.
But sometimes it can come in useful.
Koi can get MASSIVE – way bigger than a full-grown goldfish in a pond.
We’re talking up to 4 feet long!
(That’s almost hard to believe until you see it in person.)
Most Comet goldfish will never get past 14 inches max.
So next time you’re looking in a goldfish and koi pond, keep your eyes peeled for which ones look the biggest.
Those ones might be the koi!
Why are Koi & Goldfish Different Even Though They Are Related?
Yes, it is true that koi and goldfish are “distant cousins.”
But according to some sources, the reason they can be so different is because their ancestors are actually two different kinds of carp.
The common carp in Japan is said to be the father of the koi…
… Whereas the goldfish originate from the Prussian or Gibel carp (it’s debated among hobbyists).
This means though they both come from carp, they were hybridized from different species of carp with different genetic makeup.
But get this:
The two can interbreed to create sterile offspring.
(More on that in another post.)
Can Goldfish and Koi be Housed Together?
Despite their differences, slim-bodied goldfish and koi can make wonderful companions.
Both are athletic, strong swimmers with a good tolerance to cold weather.
Fancy goldfish are not as good of an option for either the fast kind of goldfish or koi due to their delicate nature.
More on that in another post as well.
Final Thoughts
Now I want to hear it from you.
Have you tried any of these methods to tell the difference between koi and goldfish?
If so, I want to hear how it went.
Or maybe you have some tips I haven’t mentioned.
Please feel free to share your thoughts in the comments below!
Featured Image Credit:Â left – freedomnaruk, Shutterstock, right: Napat, Shutterstock
Thank you so much. I am sure I’ll have no trouble identifying the difference between goldfish and kio.
Glad you found the post helpful, Nadine!
Very helpful. I didn’t have a clue. Can Koi be dark in colour, almost black and quite slender? Do they always hace whiskers?
Yes koi can be darker, almost black, especially if they are hybrids. Yes they do always have whiskers to my knowledge.
i have had goldfish and other freshwater my whole life .i recently took over an abandoned pool and with 35 feeders a pleco and catfish made it the centerpiece of what is now ajewel. my only advice is patiece. some fish out there may outlive me. too much in too small a space ended bad forme
Thanks for sharing, David!
I have a lot of no I and goldfish. I have been able to separate the from each other pretty successfully. I do however have this one fish that baffles me. It\’s about four inches long now, has large scales like a Koi but has no barbells. It\’s one of the many babies that was born in the pond when I had both no I and goldfish together. Like I said, I was able to separate them now, but I have no idea if this little guy is a Koi or not. What do you think?
May be a hybrid. The barbels don’t always show up on them.
We have had a backyard pond for 15 years. One of the peach fantail is probably about 9 years old. It has always had a big round belly but is perfectly healthy. Any ideas? I did read that it may be a variation of the fantail.
It might be a female with eggs 🙂
Hi I’ve got approx 249 koi and ? 34 gold fish as they were free I’ve kept them in a separate koi tank I’m still trying to identify them most are around four or five inches long so quite young just some are orange and black or brown some are orange and white 9 are a brown colour rest are all orange and one white I’m going through your methods and wondering how old before the barbels are showing as my biggest koi is definitely a ghost around 6/7inches doesn’t appear to have them yet I started aquaponic gardening this year hence so many fish they get lost in my five foot deep approx 15 ft long tanks with grow beds on top I’ve got three setups at the minute putting another in later in the year after I’ve poly tunnels over the present ones so I can grow all year round , I’ll let you know once I’ve sussed it out your write up was very informative thanks
Hi Meredith,
I had some plants that I wintered in a 150 gallon tub so the fish had more space for the winter (I did leave some with them). Come spring, I threw some eggs in the tub because they were left on string algae and wanted to pull that out.
Eventually cleaning out the tub, I found one small fish. Since I have koi and goldfish in my water garden, I’m wondering what it is. It’s not very pretty but have heard it can take a year to see color changes. It’s black on top with a green and silver underbelly and along the sides. Can it change colors and do you think it’s most likely a gold fish or koi? Can I tell at this early age (probably two months old) or do I have to wait?
Thank you.
Yes young goldfish are darker and get colours with age.
I came here through a link on Facebook. There was a discussion as to what type of fish a friend\’s daughter has.
She (& my daughter) won goldfish at school last year & she was talking about how big they have gotten. A person commented that she has Koi.
I doubt our school would give us a chance to win Koi & that\’s how I came to this site.
Reading this & checking my daughter\’s fish, I am now sure we do not have Koi.