How many carp love in a pond?

How many grass carp in a pond? How many grass carp does a pond need? In this short guide to grass carp, we look at the right stocking density for a pond. A bit of history: this carp originally comes from the Amur River in China (Yang tse Kiang). A grass carp grows twice as fast as a koi carp.

Many specialists recommend grass carp to keep a pond clean. Do weigh up the pros and cons of these fish carefully, though. They are not always the most suitable solution. This carp feeds on algae, but there is also a risk that it will go after your water lilies.

To stop it devouring your aquatic plants, we recommend feeding it pellets. It can also feed on blanketweed.

Updated on 1 November 2026 — The Foudebassin experts

The grass carp (Ctenopharyngodon idella)

It is a herbivorous carp native to China. It is found mainly in Chinese rivers. An adult female can lay more than 500,000 eggs.

• Family: Cyprinidae.
• Genus: Ctenopharyngodon
• Species: idella

It is used to control invasive aquatic plant growth. This carp is very fond of pondweeds and blanketweed. It is a fish that is sensitive to stress and disturbance, and it does not like being moved. It can reach 30 cm in 6 months and 70 cm in 3 years.

• Life expectancy of the grass carp: 30 years
• Adult size: 150 cm

Did you know it can eat its own weight in plants in a single day? Incredible, isn't it?! Its digestive system is not very efficient. If you want to keep plant beds in your pond to help the fish breed, avoid grass carp. Or at least reduce the number of fish.

There are 3 varieties of grass carp:

• white grass carp
• albino grass carp
• silver grass carp

The 3 Chinese carp: don't confuse the grass carp, the silver carp and the bighead carp

Sellers sometimes use the name "grass carp" for different fish. Only the true grass carp (Ctenopharyngodon idella) grazes on aquatic plants. Its two cousins filter plankton: they will rid you of neither pondweeds nor blanketweed.

Sizes and diets taken from the fact sheets of the Government of Québec, which describes these fish where they are invasive; these are orders of magnitude, not a promise for your pond.

The grass carp grows quickly and reaches a maximum weight of 35 kg in the wild.

How much does a grass carp cost?

A grass carp is not very expensive. Expect to pay around ten euros for a fish of about ten centimetres. For a size of 40 cm, it is more like a hundred euros.

How many grass carp does a pond need?

Grass carp are generally stocked in ponds at rates of 1 to 2 per 10,000 m². This rate generally clears all submerged aquatic plants and most emergent aquatic plants within 2 years.

This rate, or even a higher stocking rate, is appropriate for an irrigation pond or a fish-farming pond, because a pond manager in these situations generally prefers no submerged or emergent aquatic plants at all.

If you simply want to stock them and keep your aquatic plants, you will need to reduce the number of grass carp per m².

Density per area: what the calculation gives

The guideline of 1 to 2 carp per 10,000 m² dates from a time when people mainly talked about large water bodies. Here is what it gives when scaled down to the area of your pond: this is a simple calculation based on that guideline, not a stocking recommendation.

Legal framework: France and Belgium

In France, the grass carp appears on the list of "non-represented" fish species set by the order of 20 March 2013 (article R. 432-6 of the Environment Code). Under this text, its introduction for purposes other than scientific ones may be authorised by the prefect, only in a water body fitted with permanent devices preventing fish from moving freely to and from neighbouring waters, and only in mainland France.

In Belgium, the rules are a regional matter and vary from one region to another. Check with the competent regional authority and your municipality before buying or moving a fish.

Always check the current version of the text and the local rules with the direction départementale des territoires (France) or your region (Belgium). This page does not replace legal advice.

Alternatives to grass carp

When the pond is small, or when you want to keep your plants, other measures limit overgrowth without introducing a species:

• Manual removal (light weed cutting): remove the excess with a net or rake, one small area at a time, leaving the useful plants in place.
• Competing plants: water lilies and floating plants shade the water and use up nutrients, which slows algae down.
• Rebalancing the water: fewer nutrients, good oxygenation and beneficial bacteria limit blanketweed at the source. See our guide to blanketweed.
• Duckweed: a carp is not always the right answer. Our three-step plan explains what works.

For the overall balance, the natural pond guide puts each lever in its place.

Frequently asked questions

Read also: Natural pond: the guide to healthy water all year round · Duckweed in a pond: the three-step plan · How to stock a pond with fish

Sources

• Order of 20 March 2013 (NOR DEVL1305326A, JORF of 29 March 2013) — list of non-represented fish species, including the grass carp, and conditions for introduction
• Government of Québec, "Carpe de roseau" fact sheet — diet, size and effects on plant beds
• Government of Québec, "Vigilance : carpes envahissantes" — criteria for telling Asian carp apart