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Koi vs Goldfish, what is best for your pond? If you have tried to figure out the differences between the two, chances are that you have had a hard time distinguishing between Koi and Goldfish.

And that’s not just you! Anyone can confuse the two breeds because of their similar looks. Even though Koi and goldfish look so much alike, they are actually two completely different varieties with distinctive characteristics.

In this article, I’ll put my years of experience to use and show you some of the obvious differences between Koi fish and goldfish that should help you identify the two easily.

Trust me when I say this; after reading this article, you’ll no longer have to ask, “koi vs goldfish: which is which?”

So, let’s go fishing for answers!


It’s safe to say that Goldfish are the distant “elder” cousins of Koi fish. I’ll tell you why.

Goldfish and Koi both originated from East Asia as a result of selective breeding. However, goldfish were bred from a dull olive green colored edible fish, namely ‘Prussian Carp’.

Whereas, Koi are colorful variants of Amur carp, which emerged in the 1820s. Up until recently, it’s believed that Koi fish have been bred from Common Carp (Cyprinus carpio). Ranger Homesteading has an excellent video below that goes into greater depth about the history of koi fish.

However, goldfish are considered a species of their own, while Koi still falls under the Cyprinus carpio category.


Koi and Goldfish look so much alike when they’re young, wild, and free. However, as they age, things start to change.

The most significant difference between Koi and goldfish lies in their body shape. Koi are all almost the same size, but goldfish are usually wider and have an egg-like appearance. However, most goldfish have a variety of body types and shapes depending on their characteristics. They have dorsal fins and tail configurations with round, bulging eyes.

On the other hand, Koi have a common body shape that remains the same regardless their type with their fins and tail connected. The most interesting trait of Koi is that they possess the same body size even with different color types that leave their owners in awe.

Appearance-wise, size is the most dominant difference between Koi and goldfish. Goldfish are smaller in size and usually grow to around 6 inches long. However, in some rare cases, they might grow to be around one foot long.

Koi, comparatively grow out to be much bigger with an average size of around 20 inches to 25 inches. In some rare cases, Koi are found to be 4 feet long, if given enough food and space.

Personally, when I was new to fish keeping, I started distinguishing between goldfish and Koi based on their barbels. Barbels are whiskers at the side of the mouth. If the barbels are present, you’ve got Koi. If not, then goldfish.


When it comes to colors, the difference between Koi fish and goldfish are more apparent. That’s because Koi shows a more diverse and striking range of colors than goldfish. This may be because Koi fish are the descents of Common carp, and therefore, show colors in the metallic coloration along with red, orange, yellow, black, and white. The patterns are more unique to Koi due to their selective breeding.

Contrastingly, goldfish come in red, orange, grey, brown, yellow, white, and black with the exception of gold coloration.


One significant difference between Koi and goldfish lies in the fins and tails.

Goldfish are graced with two sets of paired fins (pectoral and pelvic) and three sets of single fins (dorsal, caudal, anal). Whereas, the fins of Koi are as simple as a fish’s fin can get.

There’s an exception in Koi varieties with long, flowy fins, namely Butterfly Koi. And even though, many pond owners love the flowy look of butterfly Koi, Koi enthusiasts do not consider them to be true Koi.

In addition to that, the distribution of fins in goldfish is highly dependent on the tails. Common goldfish might be single-tailed or double-tailed where the single varieties have a single caudal and anal fin and double varieties, such as the fancy goldfish possess two caudal and anal fins. Some goldfish, like the Shubunkin tend to have the fanciest scales and colors that Koi have.


Do you know?

The oldest known Koi in Japan lived for about good 226 years, whereas, the oldest known goldfish lived for about 43 years. Hence, this record speaks volumes about their overall lifespan.

Koi fish live much longer than goldfish. It is due to the dramatic changes in the body shape of goldfish that lessens their life expectancy.

The fun part is, both, Koi and goldfish reach their maturity by the age of two or three. However, their lifespan differs from each other. Koi fish are believed to live for about 25 to 35 years or over, while the life expectancy of goldfish is around 5 to 10 years depending on the pond conditions and nutritional analysis.


Concerning the matters of food, Koi fish and goldfish are so much similar. They both are omnivorous, lack a traditional stomach, i.e., food passes into the mouth and then straight to the intestine.

However, due to the variety in body shape and sizes of Koi. Koi Food is tailored for each size – from pellets to food sticks. Also, Koi fish are voracious eaters and might end up eating other small fish in the pond.

Compared to Koi, goldfish have smaller mouths and pharyngeal teeth to crunch the food into smaller pieces. Like Koi, they are omnivorous and enjoy flakes and small pelleted food.

Aquarium Life

One of the most frequently asked questions about Koi and goldfish is about their aquarium life.

I’ve talked about this before; Koi don’t do well in aquariums. They are born to thrive in garden ponds with at least 200 gallons of water per fish, a capacity of 1000 gallons, and in a pond at least 2 feet in depth.

Therefore, Koi demands a proper pond with optimal water level and quality. For raising healthy and happy Koi, they should be kept in Ponds, provided that the oxygen levels, diet, and water quality are top-notch.

On the other hand, goldfish are happy and healthy in aquariums, especially the fancy varieties, which are slower and incompetent than the common goldfish. Furthermore, if you decide to keep your goldfish in indoor aquariums, it’s recommended that you provide them with enough space to move around freely and grow healthily.

Compatibility with Plants

Plants With Koi or Goldfish

If you fancy submerged plants in your garden ponds, this news might disappoint you. Koi do not get along with most aquatic plants. As I mentioned before, Koi are avid eaters with bigger mouths and they ingest small aquatic plants, leaving little to no vegetation behind.

Goldfish, as opposed to Koi, are fast friends with aquatic plants and will swim around lotus and Lillies merrily, without causing any damage.

You can keep plants with Koi, but you need to be more selective with the varieties you choose versus with Goldfish.


Koi are a very hardy breed of fish compared to goldfish, which makes them a perfect fit for extreme weather. However, under circumstances, Koi develop some conditions that might cease their growth and overall performance. Some common Koi diseases are Aeromonas, carp pox, Dropsy, costia, columnaris, and anchor worms. 

These diseases are either caused by bacteria, viruses, or some parasites, and the best treatment for Koi diseases is isolation. However, the problem is, Koi is a powerful and large breed of fish. It might be a nuisance to capture them single-handedly. It’s recommended that you use a net with long handles to reach your Koi without causing much trouble.

On the other hand, goldfish may be low-maintenance and easy to care for, but they are more sensitive and demand specialized care. This is especially true if you prefer fancy goldfish.

Some of the most common Goldfish diseases are ich, flukes, fish lice, velvet, fin rot, etc., The treatment of goldfish is much easier than Koi because of the water volume. Also, goldfish are smaller in size and can be removed with a regular-sized net.


I’ve compiled a list of the most frequently asked questions concerning Koi vs Goldfish. Please don’t hesitate to comment if you have more to add.

Can they survive in the same pond?

Frankly, yes, under some circumstances.

As I discussed earlier, Koi are much larger in size than goldfish. Therefore, you would need ample space to fill your ponds with Koi and goldfish, both.
Furthermore, goldfish enjoy the company of aquatic plants while Koi will enjoy to eating most of them. Hence, there should be a partition for aquatic plants to keep the two breeds catered to and happy.

The last point is the treatment of diseases. Koi body has different requirements, and since they are graced with larger bodies than goldfish, it might be tough to catch and isolate them. Therefore, you need better nets with a solid strategy to deal with such unfortunate situations.

In addition to these points, despite being hardy and low-maintenance, Koi and goldfish demand proper attention and extensive care. Consequently, you will have to invest more time and knowledge in keeping the two together.

Other than that, Koi and goldfish get along pretty well and enjoy each other’s company. In fact, many expert Koi enthusiasts love keeping their Koi and goldfish together for ornamental purposes.

Will koi fish kill goldfish?

In my years of experience, I’ve never experienced this scenario personally. However, I believe accidents may occur only if you keep the two fish of different sizes together. Koi are greedy and voracious, and they might end up killing fish smaller than them, including goldfish. Therefore, while keeping the two together, be wary of their body size.

Are koi fish aggressive to Goldfish?

No, Koi are not aggressive to goldfish. However, there are a few exceptions, such as fancy varieties of goldfish that are unhurried, clumsy, and slow, which might not get along with Koi due to their competence for food and speedy nature. As a rule of thumb, avoid keeping Koi with any small and slow specie

Koi vs Goldfish – Which Fish Is Right for My Pond? (Main Differences)

Koi and goldfish, both are a mystical addition to your garden ponds. However, there comes a time when you have to choose between the two.

So the answer to which is right for your pond lies in your preferences, available space, and time investment.

Koi offers a rich variety of colors and different sizes to your pond. Yet, they need ample space to thrive and grow happily. You should only consider keeping Koi if you can at least manage 200 gallons of water per fish and have a pond of over 1000 gallons. The fish themselves are also more expensive than goldfish. Since they require large ponds, pond maintenance would require a proper routine with bigger and more expensive equipment to maintain water quality.

Whereas, Goldfish are much smaller in size and require at least 20 gallons of water. Furthermore, goldfish can thrive in small tanks or aquariums provided that the water quality is excellent. However, due to the varying body shape and configuration, they are slightly more difficult to take care of than Koi.

All in all, if you have a pond that is less than 1000 gallons, you should go for goldfish.

Alternatively, if you want a breed hardier than goldfish and you can invest time and money in building a larger pond, Koi would be your best bet.

Koi vs Goldfish Differences – Which Is The Best Fish For Garden Ponds?

Apart from body sizes and pond requirements, a few things should be taken into consideration while choosing between the two fish breeds.

The longevity or life expectancy of Koi is much greater than that of goldfish. Hence, if you’re looking for a long-term investment for your garden ponds, you should definitely opt for Koi.

Also, if you’re someone who admires a pet’s personality, Koi would be compatible with you. Scientists believe that Koi are more social, smarter, and have more developed personalities than goldfish. And that’s why most fish connoisseurs prefer Koi over goldfish because what’s more rewarding than keeping your fish as companions throughout your life and establishing a healthy relationship with them?

Nonetheless, both fish make excellent pets that add value, life, and intense colors to your garden ponds.

Closing Thoughts

As I promised, after reading this article, you’ll no longer feel the need to ask, Koi vs. Goldfish: which is which?

Be informed that the major difference between Koi and goldfish lies in the size, lifespan, colors and patterns, appearances, and most importantly, the presence of barbels. Other than that, both are prized pets, loved and adored by pond keepers.


  1. Hi Mark I have a very large spring-fed pond which is being overtaken by duckweed. Which type of fish will help rid me of this problem? Great article by the way

    • Hi Dianne. Pond goldfish will eat duckweed. They won’t see all of it though. I would recommend pulling what you can and having the goldfish take care of the rest. Shubunkins are a great pond goldfish to buy. Otherwise you can try comets or wakins

  2. We tried koi, they kept dying. Water tests showed it wasn’t water quality, or temperature, or oxygenation (several waterfalls) but some kept dying of cotton like growth and some died without any visible skin or other issues. Also, we never really saw them, they stuck to the bottom.
    So I gave up on the expensive fish, but rather than having an empty pond I decided to buy ten feeder gold fish for 25c each. They had a few hundred cramped in a fish tank at Petco, swimming around a dozen or more dead mates, preparing to end up as a snack for some turtle or other pet. Guess what? It’s been months and all ten are still happily swimming around. They come to the surface when they see us coming, ready for food I assume.
    So, not to disagree with your great article but my goldfish (all common goldfish, not the fancy kind) seem hardier, and less shy. Go figure, all ten for $2,50. They cheapest koi I bought was $15!
    Now I have to read up on if they can survive a winter in Utah.

    • Hi Arno,

      I don’t disagree that feeders can make good pond fish. Where I caution is that feeders then be full of diseases and can causes issues if sick. I typically recommend more classic pond goldfish like shubunkins or Wakins over feeders. While they are more expensive, they tend to be better treated and have a higher chance of being healthier and less disease-ridden.

  3. Hi mark. I have young koi and srikers mixed
    Over the last three months one yesterday. White koi hv died. I was shocked when I saw them floating. What could hv happened
    First one was summer. Second one during this week cold snap
    My 750 gallon pond is now covered with hyacinths and lettuces
    Thank you for any ideas

    • Hi Deborah. You might have some temperature issues considering you had losses in the summer and winter. Lack of oxygen could be an issue. You might want to consider investing in a pond oxygenator.

      • We have recently had a pond done for koi. We have a few small/medium koi and 2 goldfish in the pond now, we have now noticed one of our medium koi fish is guiding the goldfish to the top of the water by sitting under the goldfish’s belly, what could this mean? As google isn’t helping.

      • Are the Koi way bigger than the goldfish and are the goldfish displaying signs of stress (rapid breathing, darting when the Koi fish come close). I’m wondering if it’s an bullying issue.

  4. Hi Mark I loved this article it was very helpful to me. I do have one question. Last year I used gold fish in my outside pond and in the middle of fall I donated them back to the pet store as I live in the Northeast and we get very gold temps and lots of snow. My question is although my goldfish thrived and grew they always were hiding and I very rarely got to enjoy watching them swim about. What can I do to make them feel more safe to come out?

    • Hi Wendy,

      Yes, this is one of the other differences between Koi and Goldfish that I did not document in the original article. Koi in general are very domesticated and do enjoy the company of their owners, while goldfish are more timid due to most of them being raised in aquariums. You can train them over time to eat from your hands, but generally they are going to be more reclusive to humans than Koi. Goldfish will get more friendly with humans overtime as they get older and larger. They require more time to counter their natural tendency of seeing us as a threat.

      Mixing Koi with Goldfish will also help bring out your Goldfish to the surface. They will learn that they need to, because if they don’t, the Koi gets all the food 😅. It wouldn’t hurt to invest in a Chagoi Koi to get the Goldfish going (They are super friendly).


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