Koi or Common Carp

Cyprinus carpio

Common carp are large, greenish-brown freshwater fish native to Asia and eastern Europe. They are the first known domesticated fish, farmed for food over 2,000 years ago in ancient Rome. Common carp have been successfully introduced all over the world for aquaculture, often causing serious environmental damage in their non-native habitats. They tolerate a wide range of water temperatures and conditions, and are omnivorous, eating algae, worms, plants, snails and small insects.

For centuries, common carp have also been bred into colorful, highly ornamental pond fish called koi. Koi are usually bred for very specific patterns and color combinations, usually including white, gold, orange, black or blue. When released back into the wild, koi populations usually revert back to their natural olive-green or brown color within a few generations. Common carp are hardy and grow quickly, up to four feet long. In the wild, common carp often live for 15 to 20 years. In captivity, koi regularly live for 50 to 70 years.

Did You Know?

For centuries, Common Carp have also been bred into colorful, highly ornamental pond fish called Koi.


Does the harvest for wildlife trade or captive breeding of this species harm wild populations?

Little Cause for Concern

Koi are almost exclusively bred in captivity, and therefore the pet trade does not threaten native wild populations. Wild common carp populations are widespread throughout their native range.

EcoHealthy Recommendation:

Check that the store purchases their fish from a reputable supplier that exclusively sells captive-bred koi.

Invasion Threat

Does the release or escape of this species into the wild harm the environment and/or economy?

Significant Cause for Concern

Common Carp/Koi have been successfully introduced in many regions of the world, where they cause significant environmental harm. Thriving wild populations now exist throughout North America, South America, Europe, Africa, and Australia. Carp/Koi are usually introduced intentionally for fishing and aquaculture. Because carp are hardy and able to tolerate wide ranges of temperature, food type, and water quality, they are often very successful in non-native habitats.

Common carp/Koi root and dig in sediments, increasing the muddiness of waters where they are introduced. This often causes the death of aquatic plants and reduced survival of other aquatic species. Common carp/Koi have also spread harmful fish parasites to North America, South America, and Australia.

EcoHealthy Recommendation:

Before obtaining any non-traditional pet, check that it is legal to own one in your state of residence and check for permitting requirements. Only acquire a pet that is from a reputable breeder or dealer to ensure that you are not buying an illegally imported or wild-caught animal. Always keep your pet inside a safe and secure enclosure. Never release a pet into the wild.

Ease of Care

Does harvest, captive breeding, transport, or being kept as a pet harm individual animals?

Some Cause for Concern

Ease of care of many non-traditional pets depends on the individual owner’s years of experience and knowledge caring for a particular species. For the purposes of this website, we have geared information toward the benefit of the beginner.

Koi are relatively easy to keep in captivity and can even tolerate poor water quality for short periods of time. They may become more susceptible to disease in overcrowded conditions. Koi are not suited for indoor aquariums and do best if kept in outdoor ponds. Koi are long lived in captivity (up to 70+ years) and thus require a long-term commitment to care.

EcoHealthy Recommendation:

Before acquiring a koi, be sure to research its specific care requirements.

Health Threat

Does this animal pose a health risk to native wildlife, humans, livestock and agriculture?

Some Cause for Concern

Koi may carry parasites or viruses, such as spring viremia of carp, that harm other fish.  Koi are also known to carry Mycobacteria that can cause disease in other fish and skin infections in humans. Even healthy-looking fish may be carrying these bacteria. People with compromised immune systems are particularly susceptible to these skin infections, commonly known as “fish-handlers disease”.

EcoHealthy Recommendation:

Due to the potential for disease transmission to humans and other household pets, always wash your hands after handling a fish or touching the aquarium water. When purchasing a pet fish ask the seller if the fish or group of fish has a history of any health problems and for a list of any medical treatments the animal or tank has received.

EcoHealth Alliance works at the intersection of ecosystem, animal and human health through local conservation programs and develops global health solutions to emerging diseases.
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