Goldfish vs koi What’s the difference?

The question of Goldfish vs Koi is pretty common. It’s obvious they are related but there are some pretty clear differences as well. Have you ever wondered just what exactly separates these two closely related fish?

Well so have I! I wrote this article for myself and anyone else who wants to compare and contrast these two popular fish.

Let’s look at both species individually.

Origins of Goldfish and Koi

 

Goldfish

Goldfish were originally bred from wild carp similar to the Prussian carp. They were raised during the Jin Dynasty in China which lasted from AD 265 to 420. Originally they were raised as food fish. Later on, during the Tang Dynasty (AD 618-907), it became popular to raise carp in ornamental ponds and water gardens. These carp, through a naturally occurring genetic mutation, became gold, rather than their original silver color. 

Silver prussian carp
Silver Prussian carp

People preferred these golden-colored fish to the silver variety. These golden fish were the ones that were shown on display on special occasions.

Selective breeding of goldfish was firmly established when the Song Dynasty (AD 960-1279) rolled around. The gold color was even recognized as the imperial color. No one outside the imperial family was allowed to keep goldfish of this color.

Goldfish were later introduced to Portugal in 1611 and then the rest of Europe. They were then introduced into the United States in 1850.

Koi

White amur grass carp
The White Amur Carp

Koi are a colored variety of the Amur carp. Like goldfish, they were originally bred as food fish from as far back as the fifth century BC in China. They were known to have various colors during the Jin Dynasty. However, it was in the Niigata Prefecture in Honshu  Japan, where they were purposely bred for color in 1820. 

It wasn’t until 1914 at an annual exposition in Tokyo, that the outside world was introduced to the colored variety of koi.  They gained popularity in the rest of Japan before spreading to the rest of the world. 

Physical Differences

 

Size

It’s generally believed that pet fish tend to grow according to the size of the environment in which they’re kept. We can see this fact in play with goldfish and koi. The size of their environment has an impact on how large they will grow. For instance, in a small tank, their growth is likely to be stunted. Likewise, even the smaller varieties of goldfish can grow to eight inches in length if given the room.

The average size of a goldfish is 4 inches which is what we can see in most pet stores. If you have goldfish in an outdoor pond, however, you’ll be surprised at the whopping difference in size. Some varieties can grow as large as eighteen inches.

Koi, on the other hand, are much larger fish. They can grow up to 3 feet in length. As you can see, your regular indoor fish tank definitely won’t support these big fellas. You need to have an outdoor pond for them. 

Color

Colorful koi in pond with orange, red, white, black and yellow colors

There are over 300 varieties of goldfish in China alone. Each of these has its own unique variation in fin shape, size, and colors. Likewise, there are just over 100 varieties of koi. While koi and goldfish can be very similar in color, the koi family has a wider variety of colors.

You can even buy goldfish and koi food for color. These are designed with special ingredients to make the natural colors more pronounced.

Some of the more popular varieties of goldfish include: 

  • The common goldfish, which is the representation of the goldfish non-enthusiasts are aware of. This goldfish has a flat football-shaped body, with short fins.
  • The comet goldfish, which is similar in shape to the common, but with much longer fins.
  • The Shubunkin which is similar in fin size to the common, but only comes in a calico color.
  • The black moor goldfish is a black goldfish with an egg-shaped body and eyes which protrude from its head.
  • Fantail goldfish are egg-shaped, but with a split tail. 

Some varieties of Koi include: 

  • Kohaku are the most popular koi in Japan. These are white koi with deep red markings.
  • Taisho Sanke are white with red and black markings. 
  • Showa Sanshoku are black with red and white markings.
  • Tancho are white koi with a red spot on its head.

Lifespan

Pet fish are generally short-lived as opposed to living in the wild. Giving them proper care and a good environment can help to prolong their lives. 

In the wild, goldfish can live up to 25 years or as long as 43 years in one particular specimen. Koi are known as long-lived fish. They’ve been reported to live over 200 years.

In captivity, goldfish have life spans ranging from five to ten years. Koi can live up to 15 years, although in Japan, their life expectancy can be up to 40 years.

Habitat Needs

Koi Pond Filter in backyard koi pond

Both koi and goldfish are very hardy species and can even survive a frozen winter in an outdoor pond. But, there are some differences that need to be taken into account. 

Koi

Koi, because of their large size, need to live in an outdoor pond. Each fish needs hundreds of gallons of water to survive and prosper. When they’re small a large indoor tank might suffice. With an average growth rate of about 5 inches per year, they’ll eventually outgrow nearly any indoor tank. 

If you live in an area where temperatures can get to above 90 degrees Fahrenheit or below freezing, you’ll also need a deep pond. This means you will need to consider a pond 3-5 feet deep. They are quite hardy, however, and will tolerate a wide variation in temperature and conditions.

Don’t keep them with smaller fish, as they’ll either eat or bully their smaller companions. Males can also be aggressive towards females when they’re ready to breed. 

They’re omnivorous and will eat as much as you feed them. They always seem to be begging for food, but resist the temptation to keep feeding them. This is for their own benefit, as they’ll either overeat, or you’ll have to clean up the excess regularly. 

A combination of biological and mechanical filtration is a useful addition to a koi pond. Size the filter to the pond size when buying a filter.

A variety of water plants can be used in your koi pond. They’ll help keep the water cool and help aerate the pond. They’re also useful in keeping down algae growth.

Goldfish

Goldfish, unlike koi, can be kept in an indoor tank. They don’t grow as large as koi. Although they can survive in a small tank, at least a 75-gallon tank would be more beneficial for keeping multiple goldfish. 12 gallons per fish is a good place to start when raising goldfish.goldfish swimming around in a fishtank

 

A larger tank will help keep stable temperatures, but a heater should be used in a smaller tank.

Be careful about keeping goldfish with other fish. Barbs and tetra will have a field day nipping the fins of the long-finned, slower-moving goldfish. Goldfish also need colder temperatures than tropical fish which further limits companions. 

Additionally, they excrete a large volume of waste products, compared to other types of fish, so it’ll be a challenge keeping your tank clean.

Like koi, goldfish are also omnivores. They’ll also overeat, if given the chance, so only feed them enough to finish eating in one minute.

They don’t do well with plants as they tend to eat or uproot them. However, some enthusiasts have had success using Java fern.

Biological and mechanical filtration used in combination will help clean your tank clean with these high waste producers. A good power filter or canister filter will go a long way in keeping their surroundings clean.

They’re also excellent pond fish as they can grow quite large. A small pond will be sufficient, but the larger the better.

Here are the main differences in the goldfish vs koi debate:

  • As mentioned above, koi have a wider variation in color.
  • Goldfish have a wide variation in body and fin shape, while koi only have one common body shape.
  • Koi have short barbells growing from their lips.
  • Koi are generally much larger as previously mentioned.
  • Goldfish can be kept with other fish, unlike koi. You do have to be selective, though, and avoid the nippers like barb and tetra. If they’re cold water fish, they will make good mates as well.
  • Goldfish can be kept in an indoor fish tank as well as a pond. Koi are best kept in large ponds.

Final Thoughts on Goldfish vs Koi

You may have come to this page because you are just curious or are considering one of these two fish. Personally, I’d recommend goldfish for most people even if they are considering a pond. There are a wide variety you can choose from, they don’t need such a large pond and just have fewer problems overall.

That’s not to say I don’t love koi. If you’re willing to put in the time and money investment a koi pond can be a very rewarding hobby.

Whatever reason or interest I hope you learned something about these two iconic fish!

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