Can Koi and Goldfish Live Together?

The most common pair of tank mates when it comes to having an aquarium is the pair of Koi and Goldfish. The question arises if it is even feasible to keep these two species together. As much as the two species have been known separately for their unique physical attributes, they may be having much more in common than you think.

No, because koi can grow up to 3 feet and goldfish’s maximum size is 9-12 inches. You can put both of them in the same tank but temporarily. You have to put koi and Goldfish of the same size in the fish tank. Otherwise, the bigger fish will eat the small fish.

This article will discuss whether Koi and Goldfish can live well with each other or whether is it a risk to both species, to put them in a tank together.

Are Goldfish and Koi the Same?

If you have already kept both Goldfish and Koi separately, you may have studied or asked around about their species. These two are more similar than you would think. Here is how:

1. Omnivores

Both the Koi and Goldfish are omnivores by nature. This means that they can eat both meat and vegetable-based food. In the wild, Koi and Goldfish enjoy searching for live food and may eat up smaller fish around them. They also feed on plants and weeds in the water. This essentially means that they can both be fed the same diet, without having to worry about their specific tastes.

2. Digestive Tract

Koi and Goldfish do not have stomachs, which makes their digestive tracts very similar. Both species have Pharyngeal teeth, which means that their teeth lie towards the end of their mouths, near their throats.

3. Water Conditions

The most favorable similarity between the two species is that they both need similar water conditions to live in. Koi and Goldfish are generally hardy species of fish, which make them convenient to keep especially for young fish keepers.

1. Temperature: The ideal temperature to keep both species together is around 70 °F. Although, the range of acceptable temperature is 68 – 74 °F.
2. pH: The ideal pH of water is another important parameter for any species of fish to thrive well. Koi and Goldfish, being both hardies, can enjoy a pH range of 7 – 8.4. This shows that they live best in neutral or slightly alkaline conditions. Controlling the pH is a very important factor when keeping species such as Koi and Goldfish.
3. Water Hardness: The amount of minerals dissolved in the water is what contributes to the hardness of the water. For species such as Koi and Goldfish, the ideal water hardness is 200 to 400 ppm general hardness or GH. Since both species are known as hardy water species, one may be led to believe that tap water can be used to fill their tanks. This is the most common mistake in fishkeeping. Tap water contains minerals and chloramines which are too hard on your Koi and Goldfish. It is best to use distilled water with mineral buffers for your fish tank, or bottled water that is free of chlorine.

4. Space

Goldfish are known to grow up to 14 inches in ideal conditions, while Koi can grow up to 50 inches. This means that they both need a lot of space even when kept separately. Koi and Goldfish both enjoy a lot of space to move around and explore. When kept together, it is best that the two are kept in an outdoor pond, which will provide them with the ample space that they need.

5. Maintenance

Children are advised to keep pets so they learn discipline and responsibility, and among the most common suggestions for pets, are the Koi and the Goldfish. This means that both these species are rather low maintenance than the other fish species. They are easier to take care of and live longer than most species of fish. Keeping the two together will not affect the health or conditions of each other, as they both require similar treatment and care, and can be tended to rather easily when kept together than when apart.

6. Nature

What is the one thing that makes us enjoy the company of another person? Their personality and how it matches ours. Goldfish and Koi are very similar in that matter. Both the fish are peaceful and calm, unlike other fish that enjoy aggressiveness. Keeping the two together will not inculcate aggressiveness in either of them as they accept each other and do not bother the other specie too much.

Difference Between Koi and Goldfish?

Coming to the differences between a Koi and a Goldfish. The differences between the two are quite evident and are mostly physical.

1. Appearance

The most obvious difference between the two species is their appearance. Goldfish are generally flat and oval in shape, while Koi are much longer than Goldfish, having missile-shaped bodies. Their fins and tails also differ and in a mixture of the two, one can easily spot the Koi from the Goldfish. Koi fish comes in various colors, ranging from orange and white to blue and black. A single Koi fish can be of different colors, all vibrant and unique in patterns. Goldfish, on the other hand, is generally only available in colors such as orange or gold, black, and in some cases white. It is rare among Goldfish to be of more than two colors at once. It is the variety of colors in the Koi fish, that makes it so beautiful, and is kept mainly for ornamental purposes.

2. Size

Goldfish grow generally a foot long if they are kept in extremely favorable conditions. As for Koi fish, they are known to be as long as 4 feet, when fully mature.

3. Age

A healthy Goldfish can live up to 22 years. Most Goldfish have been known to easily survive 15 years, provided that they were kept in ideal conditions. Koi, on the other hand, can live as long as 48 years and more. A healthy Koi fish may even outlive you and your Goldfish. It is highly likely that your Koi will survive longer than your Goldfish, even if neither of them lives up to their maximum life span.

4. Eating Habits

Goldfish and Koi enjoy similar types of food, both of them being omnivores. However, their eating habits are somewhat different. Koi fish are known to dig up their food from the muddy floor that they enjoy having in their habitat. When feeding the two, you will observe Koi fish eat the food once it has hit the floor. As for the Goldfish, it will eat the food while it is still in the water. Koi fish have distinctively large mouths which help them dig food up from the mud. They have also been known to uproot the entire plant when feeding on it, while the Goldfish only nibble on the leaves.

Advantages of Keeping Your Koi and Goldfish Together

The similarities between Koi and Goldfish are evidently more than their differences. This proves that Koi and Goldfish can be excellent tank mates. For people who are willing to keep both species, it is ideal that they keep Koi and Goldfish together, as together they are easier to maintain and provide for. They also enjoy each other’s company, which keeps both Koi and Goldfish happier than they would be alone.

Why must you not keep your Koi and Goldfish together?

As minor as the differences between the two species sound, they amount to much larger problems. It is not suggested to keep the Koi and the Goldfish together if you are raising them commercially. Here is why:

1. Offspring

Since both Koi and Goldfish are of the same group, that is the carp, they can cross-breed just fine. Sadly though, their babies are not very liked among fish keepers. Their offspring may be as colorful as the parent fish, but they hold little to no value in the fish industry. The offspring are unable to reproduce, which is good since their further reproduction could have polluted the gene pool of both Koi and Goldfish. The offspring are also not as physically appealing as Koi and Goldfish, and hence not very likable pets.

2. Goldfish Reproduce More

Koi fish Do not reproduce as often as Goldfish. Throughout its life, a Goldfish can lay eggs many times, even during the same breeding season. The Koi on the other hand lays eggs once annually, and only for 5 to 6 years after being fully mature. This difference in the breeding pattern makes the Goldfish population increase rapidly. Since both species require ample space to swim about freely, this can give rise to the problem of lesser space for both the Koi and the Goldfish.

3. Koi Size

As mentioned earlier, Koi fish can grow up to 4 feet in length. This requires more space for them as compared to Goldfish. With the many babies that Goldfish produce, and the Koi being bigger in size, the space of the tank or pond can be a major constraint.

4. Eating Babies

Even if Koi are a peaceful species of fish, they are much larger than Goldfish in size. They too, like Goldfish, will eat anything that fits in their mouth. It is possible that Koi fish will eat up the babies of Goldfish which are small enough to fit in the Koi’s relatively larger mouth. This will not create aggression between the two species, but if you want your Goldfish to increase in number, it is best to either separate them from Koi or separate the Goldfish eggs once they have been fertilized, to avoid them from being eaten.

The Ideal Set-Up to Keep Your Goldfish and Koi Together

If you wish to keep the two species together, you cannot just throw them in the same tank one day. You must plan accordingly and follow certain steps to ensure that both the Koi and Goldfish are comfortable in their mutual habitat. Here is how you can do this:

1. Size of the pond

As large as a tank can get, it is best to keep your Koi and Goldfish in a pond if you wish to keep them together. Koi need more than 800 gallons of water to swim freely. A pond as big as 2000 gallons should be ideal to keep both your Goldfish and your Koi happy. Since Koi are much larger than Goldfish in size, a pond big enough for Koi should be more than enough for Goldfish.

2. Plantation

What is a pond without plants? Plantation gives a natural vibe to the habitat of your Koi and Goldfish. Goldfish nibble on the plants while Koi are known to destroy them by pulling them from the roots using their big mouths. It is best to line the walls of the pond with plants instead of adding plants in the center of the pond. Koi will find it harder to remove the plants from the edges, thus keeping your plants in place.

3. Ample Food

Both Koi and Goldfish are omnivores, which means that they cannot solely survive on fish flakes and pellets. It is best to add live food once in a while to their pond which keeps their hunting instincts alive. Live food that can be added to the pond includes bloodworms, brine shrimps, and aquarium snails. Keep in mind that overfeeding will affect the health of your fish and the pond’s water quality. Make sure to remove the food once Koi and Goldfish have eaten, which, for a pond, is ideally 5 minutes after you have added the food. You Koi and Goldfish also need vegetables in their diet, which you can add by feeding them deshelled peas, lettuce, and carrots. As for the processed fish food, any carp food should be good enough to keep your Koi and Goldfish fed.

4. Seasonal Care

Your Koi and Goldfish require different care in winter and in summer. In winter, you must not feed your Koi and Goldfish a lot as they eat less in winter. Make sure that heaters are installed in your pond, especially if it is an outdoor one. Keep in mind that the heaters only heat up the pond as much as is required. Deeper tanks, as much as 4 feet, help keep the Koi and Goldfish warm in winter. As for summers, make sure to keep your Koi and Goldfish well-fed, as the protein intake just before winter helps build up fat deposits to keep them warm in the winter. Warmer waters do not hold a lot of oxygen, so it is best that you keep a check on the water’s oxygen levels. Also, make sure to monitor your pond for pests and insects which are likely to infect and hurt your Koi and Goldfish in summer.

The Bottom Line on Can Koi and Goldfish Live Together?

Keeping Goldfish and Koi together may be a wise decision for a while, but not in the long run, especially if you wish for them to reproduce and grow in number. However, their companionship is something to enjoy. When kept together, Koi and Goldfish have been known to live happily and will not cause you much trouble.