Are Koi Fish Good Pets?

Are Koi Fish Good Pets

If you are looking for a fish species that you can closely compare to the social, interactive, and intelligent of other pets such as dogs, cats, and birds, then the Koi fish is one of the best pet fish species. As you will read further when we look at their temperament and behavior you will see why they make such interesting pets that you can quickly become quite attached to.

Koi fish are intelligent and love to interact with humans, they are hardy, but I must warn that the Japanese and Jumbo species can grow enormously large, whereas most of your domestic aquarium species are a bit smaller, but still enormous in comparison to most tropical freshwater fish.

 Koi Fish Species Overview

Koi fish scientifically known as Nishikigoi in Japanese is a brocaded (Elegant) Carp species that come in many color varieties. They similarly form part of the Cyprinid species (the largest and most diverse vertebrate fish species)

They are native to Japan and known for their decorative purpose kept in garden ponds and koi ponds. Today they are popular all over the world as ornamental pet fish kept in very large tanks and mostly large fish Ponds for their decorative colors and patterns and gentle nature.

Three types of Koi fish differentiate in size. The Domestic Koi ranges between 12- 15 inches (30.4 – 38cm) as an adult, whereas the Japanese Koi are between 22 – 26 inches (55.8 – 66cm), and the Jumbo Koi are around 34 – 36 inches (86.3 – 91.1cm).

What I love about the Koi fish species is their very long lifespan, usually between 25 and 35 years, and the Japanese Koi has a record of 40 years.

Color Variations in Koi Fish

One of the most unique and enticing features of Koi fish is their ornate color varieties The most common Koi base colors are Silver, Yellow, Black, White, Red, Gold, Pink, and Blue, with the addition of the multi-colored species that usually have a white body and two or more other color markings, or red or orange markings. Each color symbolizes a specific meaning;

  • Pink – Symbolizes Youth and Femininity.
  • Blue – Traditionally means inner peace and comfort.
  • Gold – Are known to be purveyors of financial prosperity, and luck.

Koi fish are well known for their unique and diverse distinct color patterns. They are persistent and can withstand many obstacles, as well as brave against natural predators in the wild.

Basic Care and Koi Facts

Koi are cold-water, hardy fish that need plenty of space, thus ideally they will need to be kept in a large pond, or properly set up in a swimming pool when mature, but can be kept in a large aquarium when juvenile. Most professional and advanced Koi enthusiasts have mastered pond construction for raising show-quality koi fish.

Living Environment

You can technically keep Koi in a 50 to 150-gallon tank when young, and they prefer to be kept in small groups as they are not solitary fish. Ideally, you will need a properly set-up Koi tank or pool for adult koi with proper water parameters of between  15°C-25°C (59°F-77°F), and a pH of between 7 – 9. If you intend on keeping an adult group of Koi in an indoor tank you will need a sizable tank of around 1000 gallons.

  • Filter and Heater – You can never over-filter a Koi Pond or Aquarium, and they will need strong filters to deal with a substantial amount of waste. A Mechanical filter to trap solids on the surface of the pond may be necessary, as well as a proper Bio-Filter that runs 24 hours a day for your pond. For an Aquarium you will need one or more strong filters such as a hang-on back filter. Ideally for Kois outdoors in a pond or pool a heater may not be needed, as they tend to hibernate during winter, however, you may need a de-icer to remove frost layers from the top of the water surface. In an Aquarium, you can use a heater, though temperatures need to be kept cooler and consistent. Koi prefer natural light with the shading of plants and do not ideally need artificial light.
  • Substrate and Décor – Natural pebbles, rock, and larger gravel in a thin layer will be ideal for Koi Ponds and Aquariums. Rocks and other ornaments such as waterfalls and statues are decorative for outdoor Koi environments.

Live Plants – In Koi Aquariums and Ponds, or Pools Live Aquatic plants are essential. For Aquariums, you can use the most basic Aquarium plants that are rooted or floating. In ponds and pools, the following are good options;

  • Water Hyacinth – Floating Plants that are easy to care for and produce lovely flowers.
  • Water Smartweed – A Submerged Plant that grows quite large.
  • Water Lotus – Floating Aquatic plants that provide good shade.Water Lilies – Lovely Flowering Floating plants that have striking beauty.
  • Water Lettuce – Smaller Floating Plants that similarly provide nourishment.
  • Scouring Rush – A rooted plant that helps to filter and stabilize water parameters.

Most of the plants that we have chosen have good water cleaning abilities and oxygenate the water, similarly, they can be a delicious titbit for your Koi.


Koi are known to be Omnivores and need a varied diet of vegetation such as peas, lettuce, spinach, and even some fruits including watermelon. Proper Quality Koi pellets are an essential staple food for Koi in a Pond or Aquarium. They are generally surface, and bottom feeders and can easily be taught to eat from your hand.

Other Species Companions

When choosing other fish species as companions for Kois you need to consider species that will likewise thrive in similar temperatures and water parameters. In an Aquarium, you will have more choices, whereas, in a pool or pond, you need to be more considerate. Generally most Goldfish species, Barbs, Tench, and Pleco species make good mates, apple snails are a great companion and can help to keep algae under control.


As a rule, Koi will easily breed on their own, spawning in spring and summer. The fry hatch between 4 and 7 days. Koi can produce a large amount of offspring and caring for the fry is usually better done by professionals. You may similarly need to cull or use the fry and eggs as feeder fish and protein, to prevent your pond from becoming overcrowded.

Common Health Issues

Koi fish are very hardy though they may suffer from many similar health issues as most tropical and Goldfish species, these include;

  • Ich – A protozoan Parasite that causes white spots on the skin.
  • Fin Rot – usually a bacterial infection as a result of physical damage.
  • Swim Bladder Issues – A bacterial or fungal infection that may infect the swim bladder of your Koi fish, which helps them to stay afloat in an upright position.

For most of the common pests and diseases in freshwater fish, you may be able to get specific medication from your vet or local pet store. Keep in mind any affected fish must be quarantined in separate housing with clean water conditions to prevent infecting other fish, and to help with the healing process.

Why Do Koi Make Such Amusing Pets

  • Temperament and Behaviour – To answer our Topic question, Kois make lovely pets as they have a happy and expressive temperament and they love attention. They essentially crave interaction with their humans, and can easily be trained, with long-term memory, remembering faces and even recognizing their names. 
  • Intelligence – Dogs, Birds, and many other animals are highly intelligent, but have you ever thought about fish? Did you know that Koi are highly intelligent, with limited reasoning abilities, long-term memories, and the ability to do tricks?

If taught well, and in the right environment they can;

  • Swim to you on sight, especially because they see you as a source of food.
  • They will respond to sounds and signals, such as bells and whistles, which you will need to teach consistently and reward with food or a treat.
  • Koi will swim to a target, your hand, a stick or a pole can be used. They will swim towards it and touch or investigate it, in which case they can be rewarded with food. Keep in mind that a hand or arm may not be the best target when feeding.
  • They will also quickly learn to eat from your hand when they finally learn to trust you. You can lower your hand with food in your fist and allow them to eat. This similarity creates a powerful bond between the owner and the pet Koi.
  • Some Koi may even jump out of the water for their food, though this is a much more advanced and impressive trick in Koi that are used to being hand fed.
  • Handling Koi Fish – Handling your koi fish, touching or stroking them is not a good idea, and can harm them even though they may seem to enjoy it. Koi should only be handled when necessary for a health check, or when moving them to a new living environment. Even then care should be taken and you will need to thoroughly wash and disinfect your hand and remove all jewelry that may scrape or scratch them. Hold the fish firmly but gently with its head pointing toward your body, and take care as they are notorious jumpers.

Final Thoughts

As you can see by now, Koi are the most amusing, interactive, sociable, and intelligent fish to keep as pets. They are hardy but do require large ponds or pools to flourish in. Smaller domestic Koi can be kept in very large aquariums, however, this is not ideal. Koi have an outstanding memory which is what makes them so unique, alongside their ornamental color variations that are so diverse.


Frequently Asked Questions

Are Koi Fish Intelligent?

Koi are highly intelligent and can be taught tricks. They have a highly developed long-term memory, and will quickly get to know the face, and voice of their owners, and even recognize their names.

What is the Oldest Koi Fish to Date?

It has been documented that some species of Japanese Koi fish have reached over 50 years of age.

What is a Butterfly Koi Fish?

The Butterfly Koi mainly has much longer, flowing fins that keep on growing as they get older, in comparison to regular Koi with short fins.