Common carp

Carp eat almost anything they find on the bottom.

They suck up mud, keep the food and blow the rest out. This makes the water cloudy.

Carp are omnivores, which means they eat both animals and plants. They feed on insect larvae, worms, snails and other mollusks, and tiny zooplankton, and also on the stalks, seeds and leaves of water plants.

They have a messy way of eating. A carp sucks up a mouthful of mud from the bottom, keeps the food, and puffs the rest out through its gills. This is sometimes called mumbling. It stirs up the mud and makes the water cloudy.

Common carp are bottom-feeding omnivores, eating insect larvae, worms, mollusks and zooplankton as well as the stalks, seeds and leaves of aquatic plants. They have no teeth in the mouth; instead, pharyngeal teeth in the throat process food.

Western Australia's Department of Water and Environmental Regulation describes the feeding style as 'mumbling': carp suck in sediment, filter out food items and expel the rest through the gills. This resuspends sediment and nutrients, raising turbidity, releasing phosphorus that feeds algae and preventing the growth of native aquatic plants, which is why carp can degrade the lakes they invade.

Carp are tough fish.

They can live in cold water and in water with little air in it. They travel along rivers to find places to lay eggs.

Carp are hardy fish. They can survive cold winters, a wide range of temperatures, water with little oxygen and even slightly salty water near the sea.

They are also travelers. Carp move along rivers and streams to reach good places to spawn, so once they are released into one lake, they can spread into others nearby. In spring they move into shallow water to spawn.

Carp tolerate a wide range of conditions: cold winters, low oxygen, a broad temperature range and moderate salinity. The USGS reports brackish-marsh records up to 14 parts per thousand in southern France and 17.6 in U.S. waters, and suggests carp may spread between coastal streams along the Gulf when heavy rain freshens coastal water.

Being migratory, introduced carp spread naturally through connected waterways. They are most abundant in reservoirs and in turbid streams enriched by sewage or farm runoff, and are rare in clear, cold, steep streams.

Long ago, people moved carp to new places to raise them for food.

Now some places have too many carp. Koi are pretty carp that people keep in ponds.

People have raised carp for food for a long time, and they carried them across the world. In the United States, carp were brought from Germany in the 1870s, and a government agency stocked them in lakes and rivers all over the country, sometimes pouring them from railroad tank cars into streams from bridges.

At first people were excited about carp as food. But carp soon became unpopular, because they spread so widely and made lakes muddy. Today they are found in every U.S. state except Alaska.

Carp are among the earliest fish moved around the world by people. In the United States, J. A. Poppe imported five fish from Germany to California in 1872, and from 1877 the U.S. Fish Commission imported carp from Germany and spent two decades stocking them as food fish, at times releasing them from railroad tank cars at bridge crossings. Escapes from farm ponds during floods spread them further.

The USGS notes that carp quickly fell into wide disfavor and are now regarded as a nuisance fish; they are recorded in every state except Alaska. Ornamental koi, bred for orange-and-white coloring, have also been released widely; Western Australia's koi population dates from 1947.

In some places there are too many carp, and they make the water muddy.

People try to stop carp spreading. Never let pet fish go in a lake or river.

The common carp has a strange double story. In many countries where people released it, there are far too many carp, and they harm lakes by stirring up mud and destroying water plants. The Global Invasive Species Database lists it among the world's worst invasive species.

But wild carp in their original home rivers are declining, and the IUCN lists dams and other changes to rivers among the threats. The best way to help is to stop carp spreading: clean boats and gear, and never release fish or bait into lakes or rivers.

The IUCN assessed the species in June 2022 (published 2024) as Least Concern with a decreasing native population; listed threats are dams and water management, other ecosystem modifications, and invasive species, genes and diseases. Penn State Sea Grant notes that truly native wild populations are questionable and probably few.

Where introduced, carp cause dramatic disruption: turbidity, phosphorus release, algal growth and loss of native plants. Control with poisons, barriers and harvest has proved short-lived, costly and only partly successful, so prevention is emphasized: cleaning and drying boats and gear and never releasing live bait. Western Australia's page cites an estimated 500 million dollars a year in damage from carp in eastern Australia.