Koi Carp

Koi Carp
Find out about Koi Carp. We'll learn their story, what they look like, and how they change nature in New Zealand.
Where Koi Come From
Koi Carp are special fish. They come from countries in East Asia, like China and Japan. For hundreds of years, people raised them just for decoration. They were first kept as pets in China a very long time ago. Later, they were brought to Japan. In Japan, during the 1800s, people started choosing fish with the brightest colors and coolest patterns to create even more beautiful Koi.
Koi in New Zealand
Koi Carp first came to New Zealand in the 1960s and 1970s. People brought them mainly for decoration in garden ponds and water features. They were popular because they looked beautiful.
But some Koi Carp escaped or were put into rivers and lakes. There, they started having babies. Now, they are a harmful fish that don't belong, causing environmental problems for the local nature.
Physical Characteristics
Koi fish (their scientific name is Cyprinus carpio) can grow very long, up to 120 centimeters! They have strong, long bodies with many different bright colors like white, black, red, yellow, blue, and cream. Koi first lived in Asia, but now you can find them in rivers, lakes, and ponds all around the world.
Life Cycle
Egg Stage
Female koi lay their eggs on plants underwater or other safe places. Male fish then add special cells to these eggs. The eggs soon grow into tiny baby fish and hatch out in just a few days.
Baby Fish Stage
These tiny baby fish, called fry, eat very small plants and animals. They keep eating until they grow bigger.
Growing Up
As the fish grow up, they get their special, beautiful colors and shiny scales that make them unique.
What Koi Eat
Koi fish eat many different things, both plants and small animals. They enjoy green algae, water plants, bugs, tiny crabs, and even leftover bits found in the water. Because they can eat so many kinds of food, they live well in different rivers and ponds. This is why they can become a harmful fish that don't belong in many places.
Plants & Green Stuff
Water plants and slimy green algae
Bugs
All kinds of water insects
Small Critters
Tiny crabs, shrimp, and other small water animals
Leftovers
Dead plants and other bits in the water
Where Koi Live
Koi Carp live in freshwater rivers, lakes, and ponds all over the world. They like places that are not too hot and not too cold. In countries like New Zealand, they are known as harmful fish that don't belong. This is because they can hurt the local plants and animals.
You often find Koi in slow-moving water. They stir up the mud at the bottom and pull up water plants. This makes the homes for other fish and creatures dirty and unhealthy.
Why Koi Carp Are a Pest
"When Koi carp eat, they dig up the bottom of rivers, lakes, and ponds. This makes the water cloudy and harms the natural homes of plants and other fish. They eat many things, like insects, fish eggs, small fish, and various water plants. They feed like a vacuum cleaner, sucking up everything and spitting out what they don't want. This pulls up water plants, and these plants often can't grow back. Koi carp can live in dirty water and actually help make the water quality worse."
Learn more about why Koi carp are a pest.
Different Colors of Koi Fish
Koi fish come in many different colors and patterns. Their colors can depend on their family and the place they live. You can see them with one solid color, with spots, or with swirly patterns like marble. As they grow, their colors might even change, making each fish look very special.
It's easy to tell Koi fish apart from other kinds of carp fish. Koi are usually much brighter and more colorful. They also tend to be bigger and have a stronger body shape than other carp fish.
Koi Carp Problems in New Zealand
In New Zealand, Koi Carp are a big problem for our fresh water. They take food and homes from local fish. They also damage water plants and make the water cloudy. To stop them, people use traps, nets, and walls to keep them from spreading.
Take Food and Homes
Koi Carp compete with local fish for food and places to live.
Damage Plants
They harm water plants and make the environment unhealthy.
Cloudy Water
They make the water murky and cloudy.
How to Stop Them
Traps, nets, and special walls are used to control them.
Questions
Where do Koi Carp come from, and how long have people raised them as pretty fish for decoration?
When were Koi Carp brought to New Zealand, and what was the main reason they were brought there?
What problems do Koi Carp cause in New Zealand's rivers and lakes when they start living and having babies there?
What do Koi Carp look like, how big can they get, and what colors and patterns do they have?
How do Koi Carp affect the rivers and lakes in New Zealand, and what are people doing to control them?
Answer Key
Koi Carp originate from East Asia, especially China and Japan, and have been bred ornamentally for centuries.
They were introduced to New Zealand in the 1960s–70s for ornamental garden ponds.
Once established in the wild, they damage ecosystems by disturbing sediment, uprooting plants, and competing with native species.
They can reach up to 120 cm, with a robust body and varied colour patterns including red, white, black, yellow, and blue.
In New Zealand they muddy waterways, destroy vegetation, and outcompete native fish. Control methods include trapping, netting, and barriers to limit their spread.