Koi Fish vs Goldfish: 14 Differences to Help You Decide

1. Differences Between Koi Fish vs Goldfish

1.1 Colors and Color Patterns

Koi come in a stunning array of unique color varieties as compared to goldfish. While there are certainly some stunning fancy goldfish varieties, the amount of color scope is much greater among Koi variations.

1.2 Presence of a Pair of Barbels vs None

It’s true that goldfish and koi are two fish are super easy to mistake for the other, as they look very similar. They both grow to be large, brightly colored fishes with body shapes similar enough to mistake at a glance. By far the best way to differentiate them is by the hallmark barbels (sometimes called whiskers) that Koi have, which goldfish do not.

These barbels serve an important purpose for Koi fish’s evolution as bottom feeders in murky waters, where it was hard to see their prey. The barbels have tastebuds on them and allow the Koi to feel and sense their surroundings, as well as sift through substrate and locate food- Something they are constantly doing as, like goldfish, they are voracious eaters. You’ll sometimes hear them referred to as “freshwater cows” as a result.

1.3 Origin

While Koi fish and goldfish are both carp, members of the Cyprinid family, they’re not the same fish. Koi (Cyprinus rubrofuscus) evolved from their wild form, Amur carp in the freshwaters of east Asia.

They were selectively bred in Japan as an ornamental fish from colored variations of their wild counterparts.

Similarly, goldfish (Carassius auratus) were selectively bred by ancient Chinese dynasties ornamentally; fish keepers carefully selected the colorful fish they found, and bred them to create the colorful goldfish we know today.

1.4 Fins: Attached Dorsal Fin vs Detached Dorsal Fin

Other than the whisker barbels, the other fastest way to tell the difference between Koi fish and goldfish is their fins: Goldfish have a split, slightly forked tail, whereas Koi do not. Their dorsal fins are different, too: The dorsal fin on a goldfish detaches at the back, creating a downward flowing effect (“detached” dorsal fin) whereas Koi have a dorsal fin that remains attached to its body for the full length of the fin (“attached” dorsal fin).

1.5 Flat Under Jaw vs Rounded Under Jaw

As bottom feeders, Koi have what’s called an inferior mouth. This is a science-y way of saying that their mouth opens downward, and it evolved this way to help them eat off the bottom and reach whatever is below them to scavenge for food. The area underneath their jaw is flat; this, combined with their inferior mouth and barbels, gives them the appearance of a gentleman with a mustache deep in thought.

Goldfish, on the other hand, have a terminal mouth, which means that their mouth opens right in the middle, allowing them freedom in how they feed. The area underneath their jaw is much more rounded than Koi.

1.6 More Body Weight in Front of Dorsal Fin vs More Body Weight Behind It

This difference will be hard to see, unless you have a very clear view of the fish, but it’s pronounced difference between the two carps. Most of the goldfish’s body weight is distributed behind the centerpoint of their dorsal fin, whereas for Koi, it’s the opposite: their body weight is distributed ahead of the centerpoint of the dorsal fin. This gives them a beefier look in the head area than goldfish.

1.7 Presence of Interesting Features (For Goldfish)

While variations like butterfly Koi might give goldfish a run for their money in terms of interesting features with their long, fancy fins, goldfish tend to have greater variation in features, from pom-poms on their heads to bubbly eyeballs and heads shaped like a lion’s. These goldfish differences make them unique to their koi counterparts. Here are some examples:

1.8 Body Shapes

Koi tend to have slimmer, more torpedo-like body shapes, whereas goldfish have a taller, rounder body.

That said, common goldfish, Shubunkins goldfish, and comet goldfish can have slimmer bodies, and therefore look more similar to Koi.

1.9 Lifespan

This is an invisible difference, but a significant one: Koi have a much longer lifespan than goldfish do. In a well-maintained backyard pond, Koi can live from 25-35 years, while goldfish will live from 5-10 years.

You will see wild variations in lifespan listed online for these fish; this is because they can indeed live longer under exceptionally good conditions and care, and they also live much longer in the wild. The oldest Koi recorded was over 200 years old.

1.10 Much Larger Size Potential vs Not As Large

Size is another key difference between koi and goldfish; Koi grow to be significantly larger than goldfish, and this can help you tell them apart:

Koi fish- Grow up to 3 ft long in captivity

Goldfish- Grow up to 1 ft long in captivity

The yellow goldfish average length is around 10 inches in captivity, whereas the average size for Koi in captivity is three times that.

Note that in the wild, both Koi carp and common goldfish can grow to be larger than they could in captivity. This is because they have more space and access to conditions that are difficult to replicate in a captive environment.

In captive conditions, water filtration, feeding schedule and quality, and size of the pond are key factors in determining how large these fish will be able to grow.

Because Koi are larger than goldfish, they require more space than goldfish do.

When placing them together, koi and goldfish require a significant amount of space.

1.11 Breeding & Fry

While the barbels are the best way to tell goldfish from Koi, another telltale sign of the difference is what the fry look like: Gold fish fry will always be black, while Koi fish fry will show colors even at a young age.

1.12 Price, Personality and Temperament Differences

Koi tend to be quite smart and will figure out their feeding schedule, and even come to recognize their feeder. They’re generally considered smarter and more intelligent than goldfish. Their colorations are much more varied and impressive than that of the goldfish, and because of this fantastic color variation, their larger size, and longer lifespan, they are much more expensive than goldfish.

1.13 Compatibility With Plants

This is a key difference between these two cyprinids! If you have an outdoor pond and are thinking of adding Koi, know that they will wreak havoc on floating plants. Those lovely lily pads won’t last with Koi. Goldfish, however, will be tolerant of a planted pond.

1.14 Hardiness

Anecdotally, pond keepers comment that goldfish are much hardier than Koi.

2. Snapshot: Koi fish vs Goldfish

Koi fish: Smarter, larger, more colorful/more color variations, less hardy, will destroy planted ponds. Lives longer. Needs a larger pond or tank due to their larger size.

Goldfish: Smaller, less colorful, less intelligent, hardier, more plant safe, shorter lifespan.

3. Diet & Food

Both goldfish and Koi are omnivores, which means they eat both plants and meat. Because they have such similar diets, they’re easy to keep together. Commercial Koi and goldfish breeders tend to feed 25-32% protein while fish are growing, with a focus on feeding well pigmented foods to help support the development of bright and attractive coloration in the fish.

Neither goldfish nor Koi fish have stomachs. Instead, they have one long intestine from mouth to tail. This is largely what contributes to their voracious appetites and high bioload: They are always eating as they have nowhere to store food (like a stomach). And because they are always eating, they are always pooping. While it’s popular to keep both goldfish, and Koi together in outdoor ponds, and they are a great combination, their high bioload means that you have to maintain excellent filtration and water quality in order to keep them healthy and their environment clean.

4. Goldfish Overview

Goldfish have been one of the most popular pet fish around since they were selectively bred for their colors by Chinese dynasties 1000 years ago. Fish keepers noticed that while some of the Prussian carp were dull in colors, others had bright orange hues- so they plucked the colorful ones out, put them in separate breeding ponds, and continued to breed them until we ended up with the version of the goldfish that we know today.

Contrary to the popular image of a goldfish in a fishbowl, these are actually large fish that grow to be about a foot long in captivity- Longer in the wild. When it comes to keeping them as a pet fish, they’re an excellent choice for large spaces like ponds. They’re a popular species with pond owners.

4.1 Breeding

Most goldfish breeding occurs in ponds and the typical season is the spring in the wild, triggered by the temperature increase. Fish breeders have figured out how to breed goldfish year round. As Cyprinids, goldfish lay eggs on aquatic vegetation, which hatch in about 2 to 3 days. It can take up to a year for goldfish fry to develop their bright color; until then, they’re a dull brown or black appearing color.

4.2 Habitat

As a large fish, goldfish need lots of space: about 20 gallons for each fish. This is one reason they’re popular in an outdoor pond. Smaller goldfish varieties like fancy goldfish can do all right in 10 gallons per fish.

Goldfish are freshwater creatures that prefer cool, slow moving waters with moderate vegetation. While they can and do eat plants, most goldfish are much less aggressive in their pursuit of plants than Koi are.

4.3 Colors and Appearance

Goldfish come in a variety of bright colors and combinations ranging from red, orange, red, orange, yellow, white, bronze, and black. There are some rare variations with other colors, such as Shubunkins, which can have blue color. However, the most common colors are variations of red, orange, and yellow.

Fish are typically all over solid in color or bicolor.

Note that while goldfish are smaller in comparison to koi, they’re still considered a large fish. Even fancy goldfish can grow up to a foot long in captivity.

4.4 Health and Care

Goldfish are one of the hardiest fish available in the fish keeping hobby, and unfortunately are often subject to subpar conditions. Because they are large fish who are constantly eating and pooping and therefore have a high bioload, they can dirty a tank or entire pond very quickly and this can be dangerous for the goldfish’s health. This is especially relevant when combining Koi and goldfish together in outdoor ponds or large aquarium set ups. It’s crucial to have adequate oxygenation, multi-stage filtration system, water pump, and sufficient surface area as a result. Similarly, overfeeding should be avoided.

Fun fact: Goldfish can differentiate between four different primary colors!

5. Koi Carp Overview

“Koi” is actually the word for common carp in Japanese, indicating this fish’s carp ancestors. Interestingly, in Japanese, the word also has references to “nishiki-goi” or “nishiki,” an art of fabric brocading- Along with symbolism around passion, friendship, and love. This fish has strong mythology in Japanese culture.

In the 1800s, Japanese fish keepers began selectively breeding Amur carp for color, eventually resulting in the Koi fish as we know it. This is why you’ll also sometimes hear them referred to as “koi carp.”

Tons of varieties of Kois are still being bred and developed today, and koi keeping is very much alive as a hobby and profession. From butterly koi to other koi varieties, discerning breeders are constantly developing beautiful fish. The original koi pond may have been for breeding purposes, but it quickly evolved to ornamental use.

5.1 Breeding

Unlike the goldfish, who places its eggs on dense vegetation, Koi carp lay their eggs and allow them to sink to the bottom. A sticky outer coating prevents the fish eggs from floating away.

Like goldfish, breeding takes place in spring and summer in the wild, when temperatures are warmer.

Koi breeders are incredibly detailed and selective with regards to what fry they choose to keep to sell, and to continue to breed.

5.2 Habitat

As freshwater fish that can survive colder water temperatures than tropical fish, outdoor Koi habitats should be carefully set up to accommodate the local seasons (both shallow areas and deep areas that won’t freeze over in cold temps). It’s typically recommended to shade a pond partially so that Koi have somewhere to go when it gets hot, but this can be tricky because they love to eat vegetation.

They’re not as hardy as their goldfish counterparts, so they’re more sensitive to fluctuations in the water. They’re also larger than goldfish, growing up to 3 feet in captivity, and thus require more space- Around 100 gallons per fish, but this will change according to the size of the fish. Their large size makes them ideal as a pond fish, and ill-suited to aquariums. This has contributed to the ornamental koi pond.

5.3 Colors and Appearance

Koi have significantly more extensive color variation than goldfish do; While they do exist in red, orange, and gold varieties, they also come in a breadth of color combinations from yellow to cream, to blue, platinum, and black color combinations.

Their quickest differentiating factor from goldfish is their distinctive whiskered barbels, which allow them to come through substrate and locate food.

5.4 Health and Care

Koi care and goldfish care are very similar; The primary difference is that we fish are not as hardy as goldfish, and are more sensitive to changes in the water and poor water conditions. They’re also a much larger fish than the goldfish, so it’s important to accommodate them with more space accordingly. This larger size also translates to an increased bio load in the pond, so avoiding overstocking is crucial here. Water quality should be regularly monitored and tested before adding additional stock to the pond.

6. Koi Fish vs Goldfish FAQs

6.1 Can Koi fish and goldfish live in the same pond?

Yes, Koi and goldfish can live in the same pond together well. They have overlapping water, parameters requirements, and care needs, which makes them a good combination together. However, they both contribute significant amounts of waste to the water and have a very high combined bioload, so it’s absolutely crucial to carefully monitor water quality and ensure adequate filtration and aeration with such a set up.

6.2 Are goldfish and koi the same fish?

No, but they’re related. They’re both carps from the Cyprinid family, but goldfish descended from the Prussian carp and was selectively bred in China 1000 years ago, while Koi descended from Amur carp and were selectively bred in Japan more recently.

6.3 What is the difference between koi and goldfish?

Koi descended from the Amur carp and goldfish descended from Prussian carp, so they’re two different species. Koi are larger, more colorful, live longer, and have distinctive barbel whiskers, while goldfish are smaller, more limited in color variations, and have no whiskers. Coil also have a flat jaw, whereas goldfish have a rounded jaw.

6.4 Is koi a large goldfish?

Koi are larger than goldfish, but they are not the same fish species. Goldfish and koi are two distinct, separate species in the Cyprinid family, both descended from different kinds of carp.

6.5 Should I get koi or goldfish for pond?

I think the biggest determinant for this question is how much space you have. If you have tons of space and are able to accommodate the large size of Koi, then they’re a beautiful and fascinating option. If you’re more limited in space, it’s a good idea to go with goldfish because they’re smaller and don’t need as much space as Koi do.

Another key factor here would be whether or not you want a planted pond. If you have a bunch of fancy plants planned for your garden pond, goldfish, are a safer bet.

Koi Fish vs Goldfish: 14 Differences to Help You Decide - Aquarium Passion (2024)