Koi carp have always been a colorful addition to outside ponds and water gardens. They are the domesticated version of the common carp. Famous for their beautiful colors, varieties, patterns and types of scales, the fish come into existence through selective breeding. The color of the fish usually depends on its type. Koi can be white, blue, red, black, cream, yellow, silver and golden in color. Regardless of their color, most types of koi fish are covered with different spots.
The Koi is a large fish, reaching up to 3ft in length. The size of the fish often is also determined by its living conditions. The fish thrive on adequate amounts of water, food, oxygen and appropriate temperature.

Koi fish do not tolerate drastic changes in temperature, so when you put them in a separate container e.g. while cleaning, it’s best to use water from the pond or at least water of a similar temperature. When the water temperature differs more than 18 °F (10 °C), their skin and intestines get damaged. When these injuries are too severe, they may die eventually.

When adding koi carps to your pond, start with a smaller number. They do like the company of their fellows, so it should be two or three at least. But try not to overcrowd your garden pond.

These types of fish are naturally aggressive towards smaller species, especially when they grow large. They certainly have big personalities and when alongside other fish, they usually dominate. It is advisable for koi fish to be kept alongside each other. This way, they will enjoy each other’s company and will not feel the need to dominate or turn other smaller fish into food, especially during their mating period.
If you prefer more species in your pond, you can mix koi quite well with goldfish or golden orfe.


If cared for properly, koi fish have a lifespan of up to 20 years. Proper care refers to the provision of sufficient volumes of water in spacious ponds or tanks (at least 1000 gallons of water), high-quality foods and a clean environment.

The Origin

As fish that came into existence through selective breeding by the Japanese in the 8th century (Nishikigoi), koi are descendants or a sub-species of the common carp. But even though we normally associate koi with Japan, their history seems to go back much further, and their real origin lies either in China or Korea. Some sources say there are written descriptions of colored carps dating back to 2500 BC.

A brocade koi carp.

A brocade koi carp.

How the koi eventually came to Japan isn’t quite clear. It may have been Buddhist monks who brought them with them from Korea. Other historians believe that they were introduced during phases of Chinese occupation of Japan.

However, today’s koi varieties are almost always of Japanese origin. In the 18th-century Japanese rice farmers started keeping carp in their rice paddies as an additional food source. They began to notice some color variations amongst the carp and as such, took up breeding the most colorful ones. In 1914 the Japanese prince royal Hirohito saw Nishikigoi for the first time while visiting a fair. He was enthusiastic and ordered koi to be kept in the ponds of the royal palaces from there on. This “royal warrant” gave a big boost to the koi’s popularity in Japan.
 Later in the 20th century, the koi made its way into Europe and was eventually introduced in North America. The visual appearance of the fish caught the eye of many fish farmers and pet keepers and, slowly but surely, the koi fish made itself at home in many private garden ponds.

Consequently, the breeding of the fish continued and this led to the creation of over thirteen general classes of koi carp. From Kohaku, Utsuri Mono to Kawarimono, the fish has taken the world by storm. Koi continues to evolve on a daily basis. Their growth is inevitable. Since their introduction to a bigger audience, they have never lost their place as probably the most desired ornamental fish in the entire world.


Koi fish need a lot of water to survive. However, they should be stocked based on a reasonable estimate of their full growth and not their size at purchase. The fish can thrive in ponds.

It is advisable for the fish to be kept in a seasonal pond that is at least 20 in (half a meter) deep. On the other hand, year-long ponds should be at least 60 in (1.5 meters) in depth. Water should be kept between 60 and 80 °F (16 – 26 °C). 50% of the pond should be covered in vegetation and should have a reliable source of oxygen. Koi only survive in an oxygen-rich environment.

If you plan on raising koi fish in the outdoors, your pond needs to be a minimum of 4.5 ft deep. The pond should have a sufficient waste release system. If you live in an area with very cold winters, a pond heater may be necessary.

On the other hand, if you cannot keep your koi outside in winter time, you will need a large enough koi tank or koi aquarium to get the job done. Ensure that your fish has plenty of room, oxygen, and food to ensure that it stays active. Also, there should not be a sudden decrease or increase in temperature as this will shock the fish and can harm them badly.

How to Feed Koi Fish

The best part about raising koi is feeding them! This is often a great bonding experience between you and the fish. Even though Koi are said to have a short memory, they always remember their feeder. Apart from enjoying a self-renewing supply of aquatic insects, larvae, and other plant matter, smaller koi prefer flake food while larger grown fish eat pellet food.

Three koi fish waiting to be fed

Three koi fish waiting to be fed.

When the fish do not eat well, they do not reach their full growth potential and become stunted. All koi fish can enjoy wholemeal bread and prices of lettuce. They also enjoy fruits such as slices of watermelon and oranges.

Avoid foods that are high in moisture or carbohydrates. As the digestion of the fish takes place in their long gut, it is important to ensure that koi consumes food in smaller portions. It is advisable to feed your fish three to four times a day and feed them as much as they can eat in five-minute servings. Uneaten food sinks to the ground and becomes the breeding ground for bacteria, which you should avoid.

Spring feeding

After a long winter, your koi need a lot of energy. Their fat reserves are depleted, and their metabolism increases as the water temperatures rise. It’s best to feed them with pellets which have a high percentage of protein and polyunsaturated fatty acids.

Summer feeding

In the summer the fish will have become accustomed to the higher temperatures, and you can use food with less protein and fatty acids. There will also be many plants, insects, and other small animals in your pond to supplement their diet.

Autumn feeding

Now is the time for the koi to build up fat reserves for the winter. They need high-quality food with lots of protein and fatty acids. The better you prepare them for the winter, the easier they will get through the cold period. And the more fat they can build up, the better they will be prepared for the next spring.

Winter feeding

During the winter months, the koi metabolism slows down considerably, and they aren’t very active. You should feed them a diet of high protein and only a tiny amount of carbohydrates. When the water temperatures sink below 50 °F (10 °C), you should stop feeding them altogether. With their slowed metabolism they can’t digest the food properly. This puts stress on their intestines, and their feces will consist of only half-digested food. In consequence, the water will become murky, and the nitrate levels rise.
Koi which have been fed well in autumn can get along without any food for two or three months in winter.

Breeding Koi Carp

Pure breed koi fish can be bred for a living. It is important to ensure that the fish are well fed before attempting to breed them. A koi’s prime mating age is between 3-6 years old. This is the ideal age for the fish to produce baby koi. Privacy during breeding is highly paramount when it is time to mate, otherwise, if they notice any prying action, they will not indulge in the act.

Other breeding tips include:

  • Ensure that the koi has a device such as a fry mat that will enable it to lay eggs with confidence.
  • During incubation, your fish pond water temperature should be 60-70 °F (15 – 21 °C). Do not disturb the eggs during this time.
  • Clean up the pond to improve the chance of spawning. Remember that water quality is also essential for successful breeding.
  • Protect the baby koi once they hatch as they are at their most vulnerable stage.

Koi fish are always a welcome addition to any pond. However, in order to ensure that you take proper care of them, you should understand more about them and where they come from. Make sure that you are well-educated on the particular koi breed (s) that you want to keep before buying it. You should make sure that the fish develops well and does not come to any harm in your care.