Do Grass Carp Eat Algae? [Here is The Answer]

Do Grass Carp Eat Algae

Grass carp is one of the carp species popular among anglers.

As the name suggests, grass carp eats all kinds of grass material.

When living in a pond, grass carp will feed a bit differently. So, one of the most common question about its diet is ...

Do grass carp eat algae?

Yes, grass carp eat algae! However, algae are not their preferred food source, and grass carp will consume them if other aquatic plants are unavailable. This is why some people use them for algae control in ponds.

If you want to know a bit more about algae and grass carp, read the following chapters:

What Does Algae in Water Mean?
What Do Grass Carp Eat in Nature?
Do Grass Carp Eat Algae?
Are Grass Carp Good or Bad for Ponds?
How Much do Grass Carp Eat a Day?



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What Does Algae in Water Mean?

Algae in the water are valuable water quality indicators.

Changes in their quantity can indicate certain condition changes in the water.

Algae are important for the ecosystem.

They have a short life cycle, reproduce fast and react very fast to changes in water chemistry.

When the chemistry changes, algae species composition and density will change.

Their quantity often rises, when water is full of nutrients needed for their growth. These nutrients are often phosphorus and nitrogen.

In some waters, this can indicate pollution from fertilizers used on fields near by.

It can also indicate pollution from septic systems or animal waste. Algae will grow a lot if this occurs.

Plankton algae, on the other hand, can bloom during bright, sunny, days in summer. As they rely on photosynthesis, sun is needed for their growth.

Plankton algae can be good for ponds, because they are on a bottom of a food chain.

Plankton algae are eaten by zooplankton, and zooplankton becomes food for fish.

Plankton algae are microscopic in size, and the pond where they bloom may seem muddy in color. They usually disappear after summer.

Although moderate plankton algae blooms can be good, if their number rises a lot, they can use too much oxygen from the water when decomposing after summer, and make the water bad for fish species.

If a certain algae species, called blue-green algae, occurs, the pond can even become toxic.

Shallow ponds, which are stagnant, are more likely to have an algae problem.

What Do Grass Carp Eat in Nature?

To answer do grass carp eat algae, and under what conditions, we must know what grass carp naturally eat.

Grass carp feed on aquatic plants, although they will occasionally consume insects or invertebrates.

Despite its name, grass carp is not a herbivore. Although the majority of grass carp food is plant based, it is defined as an omnivore.

Grass carp also eat some plants which are considered to be invasive in ponds, and if the carp can choose, it will mostly eat:

  • hydrilla,
  • musk grass,
  • pondweed, and
  • southern naiad.

Among these, hydrilla is definitely grass carp’s favorite food.

Do Grass Carp Eat Algae?

The answer is yes, grass carp eat algae, more specifically, filamentous algae, and can be used as a form of natural algae control in ponds.

Before you decide to get a few of them to control your pond vegetation, you should know that grass carp can be a bit picky.

You must know which plants you have in a pond, and which ones you want to control.

It can happen that carp eat the ones they like, and leave those you want to get rid of. The same goes for algae.

Carp prefers soft, completely submerged aquatic plants.

Even if other species of plants are more abundant, they will search for those already mentioned.

When favorite food source is gone, carp will eat algae and other aquatic plants too.

Are Grass Carp Good or Bad for Ponds?

Well, this is a complicated question, and the answer is both Yes and No.

It depends a lot on a specific situation, water, and which plants, or algae, you wish to control in ponds.

Grass carp eat a lot! I will tell you how much exactly in the following chapter.

If the pond is heavily stocked with them, they could eat absolutely everything in it and that is not good for both them and other fish species living there.

Using grass carp to control vegetation is cheap and easy, but the results can vary.

While in some locations this strategy showed great results, in other places it was completely inefficient.

Grass carp will eat filamentous algae, water-meal, and duckweed and for these species it is great.

However, if the pond has other species of aquatic plants you do not want to control, and want to keep them, using grass carp could end up devastating for the pond.

Another important thing to consider is: How many grass carp to use?

Overpopulating the pond is not a good idea.

Because grass carp eat a lot, you will have to use just a few of them.

Depending on a plant infestation, which can be light, moderate or severe, you should use 2-10 grass carp per acre.

I will not bother you with complex calculations, and those who are thinking about stocking their ponds with carp should inform themselves a lot and ask for advice from those who are experts.

Additionally, keep in mind that some fish species, like bass, catfish or pike, can eat small carp, so make sure that the grass carp you introduce into the pond is large enough no to end up as prey.

To be honest, you can never be 100% sure that grass carp will have a beneficial effect on a pond.

Every situation is different and requires different approach.

How Much do Grass Carp Eat a Day?

Grass carp can eat a lot!

When I say a lot, I mean 2-3 times more than it weights per day!

They can grow very big (about 100 pounds / 45kg, but specimens as big as that are rare).

It can gain up to 10 pounds (4,5kg) per year if living in good conditions.

The bigger it gets, the more food grass carp will consume.

During warmer months, grass carp eats a lot. When the winter comes, and water temperatures drop, it will still feed, just less than in summer.

Grass carp will also move less and use less energy during cold months.


Now you know do grass carp eat algae or not, and in which conditions.

Grass carp is able to control certain algae population and keep the pond clean and good.

On the other hand, grass carp eats a lot, and if the lake is overstocked, it can easily eat absolutely everything that grows in the pond.

And one last thing about grass carp;

there have been reports that introducing grass carp as a form of filamentous algae control caused growth of other algae species, not consumed by grass carp.

Although this occurrence is rare, it is not impossible.

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