Angelfish and Koi

In this post, we know a little about the interaction of Angelfish and Koi fish, in addition, we will understand some of their characteristics, requirements, and curiosities.

Angelfish and Koi

Many aquarists enjoy the idea of keeping Angelfish and Koi fish together. In general, they will not become aggressive towards each other. However, due to different tank and water requirements and sizes, Angelfish and Koi fish should not be kept together.

Koi fish or Amur carp are gentle and calm that do not tend to fight. The only situation carps are known to become a little more aggressive is when living under conditions that are not adequate and they are stressed.

Angelfish is a popular freshwater species and there are many different varieties to choose from for your home aquarium. But once you have chosen what kind of Angelfish, then there is the question of compatible tank mates. Although Angelfish are relatively peaceful and live happily with many fish species, it remains to be discussed why Angelfish cannot live with Koi fish.


Angelfish are small in comparison to the Koi fish. Therefore, they do not need as much space in comparison to the Koi fish. Thus, they are frequently kept in an indoor aquarium, along with other, similar medium-bodied fish and invertebrates. In the wild, they are native to parts of South America, particularly in the Amazon region and tend to prefer calmer, slow-moving waters. They do not like direct sunlight and will typically be found in areas that are well shaded by trees and lots of vegetation.

Thus, it is recommended to provide plenty of live plants and vegetation on the tank to simulate the Angelfish natural habitat. You might also like to provide your fish with lots of large-leafed plants.

While they are much smaller than Koi, they are still considered to be one of the larger freshwater aquarium fish and require a tank that has at least 55 gallons. However, you can go bigger if you have the space and financial resources to do so.

Concerning the water conditions, the Angelfish is an easy species to maintain. The pH level of the water should sit somewhere between 6.8 and 7.8 and the water hardness needs to be between 3 and 8 dKH, which is equivalent to 54 to 145 ppm.

You will need to make sure that the water temperature is consistent and stays between 78º and 84º Fahrenheit. Furthermore, it is important to ensure that the filtration system is in place and excellent and well maintained. It is also recommended to change at least 10% of the water every week or 25% if you are doing it every two weeks

Koi fish

Koi fish are also freshwater fish but the water conditions they require are very different from the ones required by the Angelfish. These large fish can grow up to two feet in length and this is one of the main reasons that the two should not be kept together. Koi generally do much better in a pond than in a tank.

Koi fish can be kept in fish aquariums only while they are small juveniles. Once you can move them to a pond, do so as quickly as possible. The new habitat will need at least 3 feet in depth. This is because, during the winter, there is a significant chance that the water will cool down. However, when it is deeper, the fish can swim to the bottom and avoid cold surfaces, remaining healthy and safe during the cooler months. Usually, well-cared Koi can live up to 30 years.

One of the biggest issues for fish keepers with Koi is that an imbalance in the water can cause severe health problems, and in the worst cases, death. For starters, you must guarantee that the pond has a top-quality filtration system to ensure that there is not a high level of ammonia or nitrite, which would kill the Koi fish. 

Comparison between Koi fish and Angelfish

Koi fish require higher pH levels than Angelfish, they need a pH balance between 7 and 8.5. Moreover, you need to make sure that your Koi are kept in slightly harder water as the minerals within this will prevent too many fluctuations with the pH.

In terms of temperature, Koi are very adaptable and will do good in a variety of temperatures. As mentioned, they will simply swim in the warmer depth when the water gets cooler on the surface. Some people like to include a floating de-icer during winter to create a gap in the ice that allows a healthy gas exchange, but this is not essential.

Feeding times

Angelfish and Koi fish will usually have issues concerning feeding times if kept together. Although both species are peaceful, there is always a chance of the Koi fish harming the Angelfish, and vice-versa.

When it comes to feeding, the Koi, being the bigger fish, will take over at mealtimes. They are much larger and often quicker and so when you add food into the water, they will often be the first to get it. The small Angelfish are unlikely to put up much of a food fight and thus, over time, they will not get enough food to thrive.

Can Angelfish and Koi live together?

Although both are peaceful and freshwater fish species, they should not be kept together. Both animals are peaceful and would not typically become aggressive with one another. However, while their behaviour would not be an issue, the water conditions and tank requirements might be. Koi and Angelfish require different water parameters, such as pH levels, temperatures. Thus, it is not recommended to set them up together, once there will be no adequate parameters balance for both of them.

Koi fish history and curiosities

Koi fish or Amur carp is a mutation of the common carp, usually brown. They were predominant in China. But when the Chinese invaded Japan, these fish were mainly bred for feeding purposes. Because they were very adaptable to Japanese conditions. The Japanese then noticed the Koi fish potential for ornamental aquariums. And then they started to breed them in varied colours.

They also noticed that, depending on the circumstances, the common carp changed colour. This mutation is spontaneous in the animal. At some point between 1820 and 1830, the Japanese already noticed small colour variations and thus, bred the “mutants”. From these mutations emerged the famous Koi fish.

Japanese Koi fish popularity grew very quickly. Even though in other countries people do not notice their entire beauty, in Japan, they have become one of the most desired fish. More than one hundred types of Koi fish have been registered since their creation.

The legends and references of carp

According to legend, the Koi fish were to reach the source of the Huang Ho River, which was on top of a mountain. The Koi needed to swim through stream-filled valleys, waterfalls, and cascades. The legend continues that, the carp that managed to overcome all difficulties and reach the top would become a dragon.

Because of such a legend, a rising Koi fish generally represent strength, courage, and determination to reach goals and overcome difficulties. Meanwhile, a descending carp symbolise goals that have been reached or accomplished already. Such symbols and meanings are often portrayed in the form of tattoos.


In this post, we learnt a little about the interaction of Angelfish and Koi fish, in addition to understanding some of their features, requirements and curiosities. We also understood why they should not be kept together.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): Angelfish and Koi

What do Koi fish mean?

Ornamental carp as the Koi fish appeared in Japan by genetic mutation of the common carp, originally from China. They are symbols of strength, prosperity, longevity, fortune, and fertility. 

What do Koi fish eat?

Koi fish are omnivores, with tendencies towards microphagy and/or iliophagy, feeding on small organisms found at the bottom and around submerged structures. Although, they can also be opportunistic consumers of whatever is available: plankton, insects, worms, fruits, and plant remains.

Can you put carp with other fish?

Bottom dweller fish, as plecos and catfish are also very peaceful and can coexist perfectly with carp. They like to eat the algae that are trapped in the rocks, so they are very common fish in ornamental ponds. They do not need special food and they will have everything they need for their meals on the pond.

Are Koi fish good pets?

In general, Koi fish make awesome pets for most people. They are hardy fish and can adjust to a wide variety of water temperatures. They are classified as docile fish and tend not to fight with any other fish species.

How much does a Koi fish cost?

The price of Koi fish will vary according to many factors, such as size, colour, shape, and variety. They usually cost between $50 and $150 US dollars.

Do Koi fish get lonely?

Koi fish are very adaptable fish. Thus, they can do well under different conditions. If they are alone, they will adapt and thrive. Although, this species has adopted some social and gregarious behaviours.


Watson, C. A., Hill, J. E., & Pouder, D. B. (2004). Species profile: Koi and goldfish. Southern Regional Aquaculture Center.

Sazima, I., Moura, R. L., & Sazima, C. (1999). Cleaning activity of juvenile angelfish, Pomacanthus paru, on the reefs of the Abrolhos Archipelago, western South Atlantic. Environmental Biology of Fishes, 56(4), 399-407.

Konow, N., Fitzpatrick, R., & Barnett, A. (2006). Adult emperor angelfish (Pomacanthus imperator) clean giant sunfishes (Mola mola) at Nusa Lembongan, Indonesia. Coral Reefs, 25(2), 208-208.