Fish
Carp
Cyprinus carpio · also called common carp, koi
A carp is one of the most successful fish on Earth by almost any measure — most farmed, most stocked, most widely introduced, kept in ponds as living jewellery — and in half the places it now lives, that success is a disaster. The same toughness that let people raise carp for 2,000 years lets it take over a wetland and turn the water to mud.
Overview
The carp is Cyprinus carpio, a large freshwater fish native to central Asia and the rivers of the Black, Caspian, and Aral basins and the Danube. It has a stout body, a protrusible toothless mouth with two pairs of barbels, and a long dorsal fin. It grinds food with throat teeth against a hard pad. People have spread it to every continent except Antarctica.
An ancient farm animal
Carp were raised in ponds in China at least 2,000 years ago, spread across Europe through Roman and monastic fish ponds as food for fast days, and are still the most farmed freshwater fish by weight. The ornamental koi are the same species, bred in Japan since the 1800s for colour, with top show fish worth six figures.
Built for bad water
Carp shrug off low oxygen, warm water, mud, and pollution that would kill most fish, gulp air at the surface in a crisis, and survive near-frozen ponds by slowing right down. They live 20 to 40 years and can top 1.2 m and 30 kg.
The invader
Where carp are introduced — across Australia and much of North America — their endless bottom-rooting uproots water plants, muddies the water, and fuels algal blooms, flipping clear wetlands into turbid ones and crowding out native fish and waterbirds. In parts of Australia’s Murray–Darling Basin, carp are most of the fish by weight.
Status
Wild-type carp in the native range are assessed as Vulnerable and decreasing, swamped by interbreeding with farmed fish and cut off from spawning grounds by dams — even as domesticated carp are among the most abundant fish on the planet.
Carp: common questions
Are koi and goldfish types of carp?
Koi are, straightforwardly, since they are a domesticated colour form of the common carp, Cyprinus carpio, the same species as the drab wild and farmed fish, just bred over generations for bright patterns. A koi released into a lake can revert toward wild colouration within a few generations and interbreed freely with plain carp. Goldfish are a separate but closely related species, Carassius auratus, domesticated from the Prussian or gibel carp in China more than a thousand years ago. Both belong to the carp family, Cyprinidae, the largest family of freshwater fish, which also includes barbs, danios, rasboras, and the minnows.
Why are carp such a problem in Australia and North America?
Because they change the water itself. Carp feed by sucking up and expelling bottom sediment, and a dense population doing this continuously keeps the water permanently muddy, tears out the rooted plants that young native fish and waterfowl depend on, and stirs nutrients up from the mud into the water column, where they feed algal blooms. Clear, plant-rich wetlands can flip into turbid, algae-dominated ones. Carp also breed prolifically, tolerate poor conditions that limit native competitors, and have no coevolved predators or diseases in these regions. In parts of the Murray-Darling Basin carp make up the large majority of all fish biomass.
Can you eat carp, and why is it not popular in some countries?
Yes, carp is perfectly edible and is a staple food fish across much of Europe, the Middle East, and Asia, traditional at Christmas in several central European countries and central to Jewish gefilte fish. It has firm flesh with a mild flavour that reflects its habitat, so fish from clean, cool water taste far better than those from warm mud. Two things count against it in countries such as the United States and Australia. It is bony, with a row of fine intramuscular Y-bones that need scoring or careful filleting, and it carries a low-status, muddy-water reputation. Efforts to market invasive carp as food, sometimes rebranded, have had only limited success.
How long do carp live and how big do they get?
Carp are among the longer-lived freshwater fish. Twenty years is routine, many reach 30, and verified ages beyond 40 exist, with some famous ornamental koi claimed, though not all reliably, to be over a century old. Size depends heavily on food and space. In a small farm pond a carp may top out at a kilogram or two, while in a large, productive lake wild fish commonly reach 5 to 15 kg, and the biggest exceed 1.2 metres and 30 kg. The record rod-caught common carp are over 45 kg. Growth is fast when young and slows with age, and females grow larger than males.