Koi are ornamental fish that many people keep in their outdoor ponds. They can get quite large and come in a multitude of colors and varieties, bringing interest and life to a pond. Many people underestimate just how long a koi fish can live, though. These fish can be quite long-lived when cared for properly, from 15-40 years on average depending on their location, so they’re definitely not a short-term commitment. Here’s what you can expect when it comes to the lifespan of your koi fish.
What’s the Average Lifespan of a Koi Fish?
The average lifespan of koi fish outside of Japan is around 15 years, although many people report their koi living 25 years or longer. For koi fish living in Japan, the life expectancy is greatly increased, with an average lifespan reaching 40 years.
Hanako, the longest-lived koi fish on record, lived to be around 226 years of age1! She was a Japanese native fish that was passed through multiple generations of the family of her last owner, Dr. Komei Koshihara.
Why Do Some Koi Fish Live Longer Than Others?
High-quality nutrition is one of the key elements of ensuring your koi fish has a long life. Low-quality food or food that isn’t formulated for koi fish won’t support longevity in your fish. Koi should be fed a food that is formulated specifically for koi fish, and feeding seasonally appropriate foods is ideal to support long-term health. The nutritional needs of koi fish in the summer aren’t the same as they are in the middle of winter.
2. Environment and Conditions
The top cause of short lifespans in fish is poor water quality, but fish kept in a high-quality environment tend to live long healthy lives. Maintaining water quality can mean multiple things, depending on your pond setup.
Small ponds and aquariums may need routine water changes, while large ponds won’t require water changes. Filtration that is rated for the size of your tank or pond is necessary, and if you overstock, then you’ll need an even more powerful system to maintain water quality.
Ensuring that the water in your koi’s environment is at least 3 feet deep will provide them space to escape from predators and stay warm during the winter. Live aquatic plants can help to maintain water quality, as well as provide your koi with a source of nutrition outside of their baseline diet.
The location of where koi live seems to have a major impact on their life expectancy. Koi are native to Japan, and koi that live in Japan have an average life expectancy of 40 years, but it’s not uncommon for them to exceed this age. Outside of Japan, the life expectancy drops significantly, with the average typically being considered around 15 years. There are multiple factors that may cause this notable difference, including the quality of the fish being higher and a greater commitment to the art of fishkeeping in Japan.
The Japanese have the care and longevity of koi fish down to a science. Although the average koi lives longer in Japan, that isn’t to say that koi outside of Japan that are properly cared for can’t also live for multiple decades.
Although the size of a koi fish doesn’t directly impact its life expectancy, larger koi have a greater chance of survival than smaller koi. Small koi are at a higher risk of being taken by predators, and younger fish may have a less robust immune system than older fish. Larger koi are often too large for predators to bother with them.
Healthy adult fish from long-lived breeding stock are more likely to produce healthy, long-lived offspring. Koi that are of low quality and that are left to reproduce and inbreed are more likely to pass on poor genetics and shorter lifespans than higher-quality fish. Selective breeding of high-quality fish can help ensure longer lifespans in koi fish.
Access to healthcare can significantly extend the life of a koi fish. Without healthcare, fish are susceptible to illnesses and death from things like parasites, infections, and organ failure. If you are monitoring your fish closely and providing healthcare when needed, then you are giving your fish the best chance at a long life.
The 6 Life Stages of a Koi Fish
Koi are egg layers, so female koi fish will lay eggs and a male will fertilize the eggs. A female can lay up to 400,000 eggs per clutch. In purposeful breeding situations, the eggs are removed from the parents’ environment to keep them from being eaten by the parents and other environment mates. Once fertilized, eggs will hatch in about 3–4 days.
Koi embryos are developing fish that are still contained within their eggs. The length of time a koi spends in the embryo stage is impacted by water temperature, with cooler water resulting in a longer development period. During the embryo stage, you may be able to see small details of the fish forming within the eggs, with eyes being the most distinctive thing to spot.
Larval koi can also be called hatchlings. These tiny fish have just left the embryo stage by leaving their eggs. In the larval stage, koi won’t need to eat. They will continue to absorb nutrients from the remainder of the egg, which will remain attached to the abdomen for the first few days. Koi may stay in the larval stage for anywhere from 2–7 days.
Fry are newly hatched koi that have left the larval stage and are now requiring food. They are very small in this stage, often only measuring around 7 mm at the time of hatching, so very small food is essential to the survival of koi fry. Infusoria is often the first food offered to koi fry, but as they grow, larger foods, including daphnia, finely crushed flakes, and fine-grained pellets can be introduced.
Koi enter the juvenile stage somewhere around 30 days of age, although this can vary based on water temperature, nutrition, and genetics. As they enter the juvenile stage, koi will begin to develop colors and take on a more noticeable “koi” appearance. When they are in the larval and fry stages, they are clear and have a generally nondescript appearance, but the juvenile stage will bring about notable changes that will help your koi start to look like the real deal.
6. Mature Adult
Female koi fish will reach sexual maturity around four to six years of age. It takes around a year for a female to develop the eggs she will lay, and these eggs will begin being produced within the body once she releases the last clutch of eggs for fertilization. Male koi reach sexual maturity between 3–5 years of age, and they can begin fertilizing eggs at this point. It is possible for koi to reach sexual maturity at an earlier age, though, and it’s not unheard of for a koi to continue to reproduce beyond these ages.
How to Tell Your Koi Fish’s Age
Believe it or not, you can determine the age of a koi fish in a similar manner to how you can tell the age of trees. As they age, koi develop rings around their scales, with a new ring appearing approximately every 2 years. The ability to determine a koi’s age this way is how it was verified that Hanako, the 226-year-old koi, was around the age she was believed to be.
Koi fish are wonderful, social fish that people love to keep in ponds. They are a long-term commitment, though, with many koi living for multiple decades. In some cases, you may even luck into a koi that outlives you. Providing your koi with excellent, high-quality care and nutrition will provide them with the best shot at a long, healthy life.
Featured Image Credit: Quang Nguyen Vinh, Pexels