Koi Fish vs Goldfish: What Are The Differences?

The glorious multi hues of golds, reds, and oranges, mean that at first glance you may not notice the difference between koi fish and goldfish.

Both species have their own beauty, and there are many similarities - enough that you can easily mistake one for the other.

Goldfish and koi are actually different species, and they require unique care. If you’re interested in getting koi or goldfish for your pond, it’s vitally important to know what these differences are.

Treating a koi like a goldfish and vice versa will leave you with some rather unhappy fish.

This guide can explain to you the key features that separate a koi from a goldfish. Knowing this can help you make the right choice for you, and keep your fish healthy.

History Between Koi and Goldfish

Starting from the beginning, it’s easy to see where all the confusion comes from. Both koi and goldfish are descendants from the carp.

This makes them (very distant) cousins, and explains some similarities of features. 

However, a long time has passed since the goldfish began its journey from boring Prussian Carp to the delightful varieties we see today. 

It may seem strange, but early versions of goldfish were originally kept for meat during the Jin Dynasty in China.

These fish may have tasted good, but they weren’t very interesting to look at.

However, nature would throw up the occasional mutation: a normally gray fish that was vibrant with orange and yellow coloring.

These unusual fish would be saved from the cooking pot, and kept in a separate pond. They began to breed, leading to colorful offspring.

Through the Tang Dynasty this practice developed, and by the Song Dynasty in AD 960 - 1279, selectively breeding carp was a firmly established pastime.

Goldfish are now classed as their own species - Carassius Auratus.

Koi are a more recent enjoyment, and a type of Amur carp. Although breeding carp for color variations dates back to the Jin Dynasty, ornamental koi weren’t systematically bred until the Japanese started the practice in the 1820s.

These fish, named the nishikigoi, are the koi we know today.

Physical Differences Between Koi and Goldfish

Now, we will take a look at some of the main physical differences between both koi and goldfish.

Differences in Size Between Koi and Goldfish

If you have a 4-foot fish, then you have a koi. While it’s very unlikely for your koi to grow to this size, it isn’t impossible. However. a 4-foot goldfish would be a genetic marvel. 

So, if you happen to come across a 4-foot fish in a pond, it’s undoubtedly a koi.

While most koi won’t grow to 4 feet, they are still longer than the goldfish. The average size of a koi carp is between 2 and 3 feet in length. Goldfish are unlikely to grow up to 12 inches.

This initial size difference is a major giveaway, but there are a few other indicators in body shape.

A koi, no matter the size, retains the same elongated body shape we associate with carp. A small koi and a large koi will have the typical long, thin, and stretched shape.

Goldfish, however, have a lot more variety. On average, the goldfish is rounder and more egg-like in shape.

Some goldfish retain the elongated shape of a carp, while others are quite wide. Some goldfish have bulging eyes, others flowing tails, and double fins.


One distinguishing feature of the koi is the presence of barbels. These are like whiskers, and they can be found either side of the mouth area.

Koi have two sets of barbels, one short and stubby, and one which is significantly longer. If your fish has a pair of barbels, then it’s a koi!

Barbels are used by the koi to help them detect food when it’s hidden in murky water or under sediment.

Barbels contain taste buds, which help the koi find food enzymes floating past them in poor light.

In fact, the mouth area of the koi is quite distinctive. Koi have a downward facing mouth, with a flat jaw on the underside of the head.

Goldfish tend to have a more rounded jaw. Koi use this jaw and mouth shape to forage for food that has fallen to the pond flaw.


The fin differences between goldfish and koi are an easy way to tell them apart. The only reason it may get confusing is because of how different a goldfish's fin can get - even when compared to other goldfish.

Koi fish have basic fins, and they remain standard across the species. The fins very much resemble those of a carp. 

There is a variety of koi known as the Butterfly koi, that has long and flowing fins. While these are a popular choice for backyard ponds, true koi enthusiasts don’t consider them to be proper koi.

While the koi carps fins are simplistic, the goldfish fins are anything but. Goldfish have two sets of paired fins; the pectoral and the pelvic.

On top of that, they have three single fins; dorsal, caudal, and anal.

There’s a large variety in where these fins are placed, the size, and even the amount, across the goldfish species.

Known as the ‘fancy goldfish’, double-tailed fish have two caudal and two anal fins.

The tail itself, or the caudal fin, is another feature that’s standard on a koi, and varying on a goldfish.

A goldfish species such as the shubunkin has a deeply forked tail, with an elegant and exaggerated flow. Common goldfish generally have shorter tails, for easier swimming. 


One of the reasons koi have become such a popular and beloved fish is due to the color variation they show.

There are over 100 different types of koi, each with a unique and distinguishing feature. 

Koi have been bred specifically for the complex colors and patterns. The kohaku is perhaps the best known, and it's white body with red markings make it a continuously popular addition to any pond.

Varieties such as the showa sanshoku, black with red and white markings, and the asagi, blue on top with orange below, show just how beautifully diverse koi can be.

While goldfish do have patterns and marking, they aren’t as prolific as the koi. Goldfish tend to be red, orange, or white, sometimes with black markings.

Although many of them do have attractive color patterns, they’re more likely to be standard shades. Gray, brown, and blue goldfish can also be found. 

There are also yellow goldfish, although these are less common. They were once outlawed, as in Ancient China yellow was considered an Imperial color, only suitable for stately families.

Yellow goldfish are quite easy to breed, so numbers are increasing.

Diet Differences and Similarities

Both koi fish and goldfish are omnivores, but the ways they eat and the food they consume are quite different. Their feeding has adapted to suit the unique body of both species.

As omnivores, koi eat food including crustaceans, worms, insects, plants, and fish eggs. A koi will even eat a smaller fish, if the opportunity presents itself.

As pets, koi are generally fed sticks and pellets of food. These are specially formulated to fit the size, and even the time of year. In winter, pond koi often don’t require feeding.

A goldfish may technically eat many of the same foods as a koi carp, but they can’t live on the same diet.

Goldfish have smaller mouths and smaller bodies, meaning they can’t eat the same amounts and need smaller pellets or flakes. 

Neither type of fish has a stomach, so food is digested quickly to absorb nutrients. For this reason, you need to be careful not to overfeed.

Fish don’t really know when to stop, and their lack of stomachs means overeating can have disastrous consequences. 

What are the Differences in Habitat?

Koi are undoubtedly the bigger fish, so they need more space to be happy. That doesn’t mean goldfish don’t need room, just that they can live healthy lives in smaller spaces.

Because of this, koi do better in ponds, but goldfish can live in an aquarium tank. As a koi can grow up to 3-feet, it’s very difficult to find a tank big enough to accommodate their needs. Any tank would need to be at least 125 gallons, preferably more.

Ponds can be bigger, they tend to have better oxygen, and the temperatures suit koi. Owners will enjoy the pond, as it allows them to view the koi from above, to fully appreciate their amazing patterns.

Goldfish thrive in aquariums - as long as they’re a decent size. You should never keep a goldfish in a fishbowl, as there isn’t enough room to swim. A larger tank leads to a happier, healthier goldfish.

Be careful of the plant life you put with them. While a garden goldfish will leave most plants alone, a koi will happily eat anything it finds.

Many backyard enthusiasts have had their beautiful pond destroyed by the large mouth of a koi.

How to Handle Both Koi Fish and Goldfish

A goldfish is relatively small. They’re easy to handle, including taking them to the vets if they get ill.

Goldfish can be caught using a standard aquarium net, and even the larger varieties will fit in your hand.

As they need less space, cleaning the tank is easier. Water changes don’t need to take very long, and can be completed with little effort on a regular basis.

Koi are significantly larger, which does make them more difficult to deal with. A fully grown koi can be powerful, so catching one in the event of illness is not a fun task. A wide net is required, and things only get worse when they’re out of the pond.

Both hands are necessary to keep an unhappy koi in place. Maintaining a large koi pond is also a harder task than taking care of an aquarium tank.

Both koi and goldfish are surprisingly friendly, and can be taught to eat from the hand. Hand feeding koi is particularly enjoyable, as they poke their mouths out of the surface to get to the food.

Lifespan and Health

The oldest recorded koi was Hanako, who lived to 226 years of age. While there is some debate around the actual longevity of Hanako, there’s no doubt that the koi are a long living fish.

The average life span is between 25-35 years, and some koi can make it to 50. Goldfish aren’t known for their longevity, but they can reach an average age of 10-15 years. 

Unfortunately, many goldfish don’t live this long due to poor conditions. Goldfish that are forced to live in cramped fish bowls are unlikely to be healthy, reducing their lifespan significantly.

Although koi do have the greater average lifespan, both koi and goldfish can be companions for a decent period of years. They just need the correct love and attention.


The most expensive koi carp solid for 1.8 million dollars, but yours doesn’t have to cost anywhere near that much.

Expensive koi carp have unique and unusual pattern variations, but they also have a valued lineage. Like purebred dogs, koi with a proven bloodline are worth big bucks. 

Koi can be bought from anywhere between $10 and several thousand dollars, but many will choose to pay a couple of hundred dollars.

After the initial cost, koi are more expensive to keep. They require more food, and they need a larger pond.

While some goldfish do sell for several thousand dollars, it is easier to pick them up at a lower price.

Many goldfish can be bought for less than $10. Goldfish food is also cheaper, and the tanks are cheaper to maintain.

With both koi and goldfish, the expense comes mainly from the color variations. Although we may be a long way from Jin Dynasty China, many of the same qualities are still prized.

A goldfish with rare and unusual patterns will generally be more expensive than those that seem basic in comparison.

The luxury and care needed in selectively breeding koi and goldfish mean the greatest types are the domain of the very rich. Luckily, the less expensive variations allow us all to have a chance to enjoy these splendid creatures.