Last Updated on February 28, 2021 by Cooper Fulton

Will Koi Eat Goldfish?

When people first think of koi and goldfish, their first answer would be “they do not like each other.” ThatWill Koi Eat Goldfish is where those people would be wrong. Koi and Goldfish are like two peas in a pod, but will koi eat goldfish, even on accident?

Koi are opportunistic feeders, meaning they will eat anything they can fit in their mouth. Koi do not target goldfish but will eat them if small enough. Koi are also known to eat fish eggs if not hidden well enough. 

Koi and goldfish are one of the best pond mates if they both signed up on tinder, they’d both swipe right on each other. (they like each other).

Before considering koi feeding habits, or if you’re wondering “will koi eat goldfish” a brief description of the evolution, origin, and history of koi and goldfish is necessary to understand the relationship between koi and goldfish.


Evolutionary Origin of Koi and Goldfish

Goldfish were bred from an ancient Asian Carp – Carassius gibelio.  The history of ornamental fish keeping and breeding dates back to the Jin Dynasty in China.

Silver and grey species of carp were observed to produce color mutations ranging between red, orange, yellow, and other colors.

At that time golden color was considered royal color and a sign of prosperity. Royal wives were gifted golden fishes at their wedding.

This led to widespread breeding and variety development of goldfish. It was considered a symbol of good luck, harmony, and fortune. It was then transported to other parts of the world like Japan, Portugal, Europe, and America.

Over time, multiple subspecies of goldfish were cultivated, providing an assortment of options for size, shape, coloration, and pattern. Today their enormous varieties (ranging between 200-400breeds) are considered fancy goldfish.

Koi fish originated from Japan it is the colored and typical bred variety of common carp Cyprinus rubrofuscus or Cyprinus carpio.

It has several names as Goi, Nishikigoi, etc. Koi represents an array of different and beautiful colors, patterns, scaling, and bleaching; adding flair to an ornamental pond.

Most commonly occurring koi fish have red, white, orange, blue, black, white, yellow, and cream variants.

There are about 13 classes of koi fish with different subtypes depending upon their appearance, color variation, scale arrangements, and patterns. Gosanke is the most popular culture variant of koi originated from Showa Sanshoku, Taisho Sanshoku, and Kohaku varieties.

Today modern koi provides an incredible and diverse choice to choose your pet from 100 different varieties.


Will Koi Eat Goldfish?

Will Koi Eat Goldfish?

So, will koi eat goldfish? Koi have zero cravings for goldfish, period. A Koi’s diet consists of algae to small insects to even store-bought cereal.

If you ever need some company, you can pour out some cereal and take out a lawn chair and sit by the pond while you and your koi friends enjoy a silent joyful breakfast together.

So, no. Koi will not eat goldfish.


Will Koi Eat Goldfish Eggs?

Yep. Unfortunately, they will eat goldfish eggs and even their own eggs as a little snack.

Both koi and goldfish are omnivores meaning they’ll eat both plants and insects. So, both koi and goldfish will eat eggs.


What Should I Feed My Koi Fish?

What Should I Feed My Koi Fish

Koi and goldfish both belong to the carapace family. Both share the same ancestral origin so they are considered cousins.

However, Koi fish is double in size paralleled to goldfish, it requires a double amount of nutrition as compared to goldfish.

Koi fish need more protein, healthy fats, vitamins, and minerals.

Koi are also considered as dogs of the sea as they will eat everything involving human food, vegetables, algae, bugs, insects, small fishes, fish food, etc.

Whatever is provided will be their food. Both the species are submissive, however small-sized goldfish (1inch) can be misguided by koi for food and can be pelleted by koi fish.

Koi will not attack an injured or sick goldfish as they are cousins but sometimes a larger koi fish will need smaller fish to fulfill its appetite.

Koi are omnivorous in nature and can eat a variety of plants, insects, fish eggs, and algae. Koi has a larger appetite, it enjoys eating all the time on and off at intervals.

It requires a large amount of proteinaceous food. Sometimes koi may eat spawn, eggs of goldfish, or other fishes residing in the same pond.

It can even eat its own eggs. This does not prove them as aggressive ones, they are submissive species but their ever occurring appetite and low feeding misguide them to mistake small fishes as food.

If they approach a fish and consider or realize it like a fish, they will not eat that fish leaving that fish alone. Koi can easily live with submissive and docile fishes like goldfish.

Koi fish eat all the time, it enjoys and loves food.

What Should I Feed My Koi Fish

It does not mean that koi is picky about food, they will eat everything fish spawn, eggs, shrimps, larvae, snails, tadpoles, crustaceans, mollusks, floating and submerged plants, cucumber, lettuce, carrots, peas, bread, chocolates, cakes, biscuits, pellets, and many other things.

They can eat goldfish in a rare case, not only goldfish other small-sized fishes too. But this can happen rarely.

Koi do not eat smaller fish and are happy to live with as many fish as they can. Even if a tank is overcrowded or the koi are underfed, they are not known to attack each other.

They will also not attack goldfish or other fish, such as plecostomus and other feeder fish. Koi do not view other fish as enemies and will strive to avoid conflict with all other fish.

To avoid your small goldfish to be eaten, Koi should be fed two to four times per day in summer months, when their metabolism is faster especially.

Their food may equate to the size of your stock. 30-40% aquatic sourced protein, healthy fats, low ash, and a wide vitamin and mineral profile is the essential component of food pellets.

Many commercial feeds are not of good quality to maintain your fish, you will need to add food and look keenly for the best quality of feed providing the highest and qualitative nutrition. Ensure your koi is properly flourishing and developing not just surviving.

As with koi, the standard goldfish feeding frequency is two to four times per day but should decrease jointly with temperature.

As opportunistic feeders, goldfish will continue to eat, if food is provided to them – a useful mannerism in the wild where food is not always abundant and there exist competition and natural selection, but deadly in captivity.

Standard goldfish food is rich in carbohydrates but relatively low in protein, similar to commercial koi feeds.

Again, you should opt for a higher quality feed that provides all the ingredients goldfish need to grow strong and healthy.

Next to maintaining good water quality, having a good quality feed is probably the second most important aspect of optimal pond keeping.

Overall, the feeding and water quality requirements of goldfish and koi are similar. The main detail to bear in mind is that koi are larger than goldfish.

As such, they require a more sizeable pond, more food, produce more waste, and necessitate stronger filtration equipment.

This all equates to more monthly costs and initial investments!


Differences Between Between Koi and Goldfish

Common Differences Found Between Koi and Goldfish

Understanding the main differences between koi and goldfish is an important character to distinguish them and observe their relationship in pond and aquaria.


Color variations

Goldfish can have various colored varieties involving red, orange, yellow, white, and black. Similarly koi fish can produce the same colors but their pattern is different.

One can differentiate them with large contrasting color patches easily visible on koi fish bodies.


Fin curves variation

To differentiate koi from goldfish you have to look keenly upon upper dorsal fins, in koi, it will be curved outside while in goldfish it will be curved inside.


Barbels existence

Koi has slender, horn-like whiskers around the mouth and chin that act as sensory organs while goldfish lack any barbell, whisk, or slender.


Size Variation

A fully matured goldfish will attain the size of 8-16 inches, while koi is a large fish attaining the size of 1-4 feet.

Koi grow an average of two centimeters per month, often-times reaching a maximum length of over 3 feet (sometimes considered “jumbo”).

When properly taken care of, most live to be approximately 50 years old – a key fact to keep in mind when deciding whether or not to have them in your pond – but they can live to be over 100, and the oldest known koi lived to be 226!

Goldfish, on the other hand, have more variation in size and shape depending on the variety.

Some may be only a couple of inches in length, and at most will reach a foot long.

Oftentimes, goldfish are associated with a short lifespan.

This is more often than not an unfortunate result of inadequate care, as goldfish can easily live an average of 10 or more years in good conditions!


Tail variation

Koi fish have the same type of tail while goldfish may show variation in the tail and their patterns of swimming.


Eye variation

Koi fish have the same type of eyes while goldfish can have a variety of eyes like bulging eyes, three eyes, tadpole eyes, condensed eyes, etc.


Filtration variation

Koi requires proper filtration and aeration unit to survive best while goldfish can live without oxygen for a week. Goldfish do not require much filtration.



Koi are much larger than goldfish, but can withstand low temperatures and will hibernate during winter.

Koi is a fairly resilient species, able to resist many parasites and diseases that are known to impact numerous other freshwater fish.

However, they are susceptible to koi herpesvirus (which many are born with) and survive the best in a pond environment with low waste, high aeration, and stable water parameters.

The biggest threat to koi are sudden changes in water quality and their environment, so keeping things stable is one of the most important aspects of koi keeping.

Water quality should be tested regularly to ensure optimal parameters are met and there are no sudden changes.

Goldfish are also considered to be quite tough so long as the water is properly filtered and oxygenated, and in outdoor ponds can withstand surface ice formation for short durations (though it is recommended to transfer them indoors if temperatures may drop that low), or install some winter protection equipment to be safe.

In general, the ideal temperature range for goldfish is 68 to 72 degrees Fahrenheit.

While able to tolerate fluctuations in pH levels better than other fish species, a pH of 7.2 to 7.6 is best.

Many fancy goldfish varieties are more prone to illness and disease than koi, but again this is primarily due to deficient care or being kept in too small of a space, such as a fishbowl.


Pond requirements

Koi will be most comfortable in larger ponds but can survive in smaller environments if water filtration is high capacity.

Since koi can grow to be rather sizeable depending upon the variety, your pond size and how many fish you decide to have should be based on their average adult size and not their size at the time of purchase (they will grow – fast!).

A general rule is 1 inch of fish for every 10 gallons of water, but because koi add significantly to your pond’s bioload (waste levels) due to their larger size, you should have no more than 4 koi per 1,000 gallons of water.

Still, many argue that 1,000 gallons is simply too small to allow adult koi to move about and live comfortably, and an even larger would is more ideal.

Although you may see a large amount of koi packed into a small space when you go to purchase them, the breeders likely have massive filtration systems in place to handle the large bioload.

Likewise, the koi won’t be in that small environment for long, so it should have a little negative effect on their health.

Will Koi Eat Goldfish

If you intend to keep koi personally and don’t want to spend thousands on expensive filtration equipment, you need to make sure your pond is large enough for them to thrive for the rest of their lives!

Contrastingly, goldfish are of course smaller than koi and naturally require less space, though pond size guidelines are somewhat contingent on the goldfish variety.

As before, the commonly accepted rule is 1 inch of fish per 10 gallons of water.

This is still commonly debated, however, as all fish are different. Fancy goldfish, such as Pearlscales can be kept in small ponds or large aquariums due to their size.

Smaller fancy varieties of goldfish seem to do well with 1 fish per 10 to 20 gallons, while larger breeds such as the common goldfish and comets need at least 20 gallons per fish.

Again, all fish are different and you should make certain that you conduct plenty of research before choosing a particular pond size or goldfish breed.

For instance, pearl scales are considered a small to medium-sized fancy goldfish breed and yet require a minimum of 30 gallons of water per fish to flourish because they generate a surprising amount of waste.

Conversely, if you like the idea of having fancy goldfish more than having an outdoor pond, it may be easier (and cheaper) to simply purchase a large indoor aquarium instead.

This would make cleaning and maintenance easier, and they’d already be nice and cozy during the winter.