Pond Boss Magazine: Moderators' Corner

Grass carp can be extremely effective for certain aquatic weed problems—but only against those choice plants they are capable of controlling. They are not a cure-all for aquatic vegetation problems. Too many grass carp can quickly lead to even more and difficult problems. They are also a lot of fun to watch and grow to look like silver torpedoes in the water.

The Pond Boss Forum gets lots of questions about algae, weeds, and other desired and undesired growth in ponds. Most questions can be readily and accurately answered, but it is extremely important to know what kind of growth needs controlling. Identifying problem aquatic plant growth is Job One. Is it algae? Is it rooted? Is it submersed? Is it floating? Is it …?

Providing photos of what the problem looks like in the pond, and taking photos of samples becomes extremely important in determining if grass carp can be one of the solutions to the problem. This is where the Pond Boss Forum can be of immense assistance, oftentimes very quickly, accurately, and effectively. The photos below are from a decorative pond in southern North Carolina that receives runoff from highly fertilized yards and a golf course.

Grass carp are much like medical prescriptions or other procedures recommended by competent and experienced medical professionals.

A very important step to becoming a medical doctor is taking the centuries old Hippocratic Oath. One of the promises within that oath is “first, do no harm” which is a direct translation from the original Latin -- “primum non nocere”.

Most aquaculture professionals want follow that important guideline by starting with the lowest level of risk to cure a problem. It is much like the medical community determining the best course of action for a medical problem without doing extra harm.

Pond dye was the first step in trying to prevent the pond problem shown above. Pond dye limits the amount of sunlight getting to the plants. If the problem isn’t too bad, this method can work. It didn’t work here.

This pond is an extreme example compared to most fish ponds. It has a near continuous inflow of water from underground and from runoff. It is in a housing and condominium development surrounded by a golf course. The grass covered areas and other plantings receive extreme amounts of chemicals and fertilizers. To add to that, the pond receives a tremendous number of commuting and resident wildlife visitors during each season. The visitors include many different types of birds. It also includes several kinds of turtles and, of course alligators. These migrating creatures can easily transfer many different kinds of invasive aquatic plants with them.

In this particular pond I found that the problem was bad enough to require a multi-faceted approach.

● Mechanical removal

● Renewed dye treatments

● Aquatic herbicides

● GRASS CARP

In this pond, for dye to be at all effective, it must be applied quite regularly because of the rather high volume water flow-through.

Being that this past winter was the first serious effort at attempting to clean up this pond (except for previous dye treatments by the grounds crew), we decided to remove as much of this season’s new growth with rakes. The pond surface has an area about 2000 square feet at full pool. We drained it down to about half of that and started raking. The problem with raking is that this particular weed regrows from broken off fragments, and it grows pretty fast.

In this pond I only added four grass carp in hopes that they will eventually control the weeds.

Within about three weeks of adding the grass carp the growth had come back extremely thick and heavy. It was then decided to use an aquatic herbicide with a surfactant to further help control the growth and give the fish a head start. I was only able to treat about half of the pond before I had to leave. (This is at our winter home.) Someone else will be treating the remainder. It is important not to kill all of the weeds at once, as the decaying plants will consume oxygen in the water, which can adversely affect other aquatic life in the pond. In this case it involves lots of turtles, frogs, other amphibians, and a variety of bucket-stocked bluegill and largemouth bass.

I figure it will take a couple of years to have the grass carp controlling the growth in this pond.

What are Grass Carp?

From Wikipedia - Grass Carp

“The grass carp (Ctenopharyngodon idella) is the species of fish with the largest reported production in aquaculture globally, over five million tonnes per year.^[1] It is a large herbivorous freshwater fish species of the family Cyprinidae native to eastern Asia, with a native range from northern Vietnam to the Amur River on the Siberia-China border.^[2] This Asian carp is the only species of the genus Ctenopharyngodon.

It is cultivated in China for food, but was introduced in Europe and the United States for aquatic weed control. It is a fish of large, turbid rivers and associated floodplain lakes, with a wide degree of temperature tolerance. Grass carp will enter reproductive condition and spawn at temperatures of 20 to 30 °C (68 to 86 °F).^[2]^[3]

In the United States, the fish is also known as white amur, which is derived from the Amur River, where the species is probably native, but has never been abundant.^[2] This is not to be confused with the white Amur bream (Parabramis pekinensis), which is not a particularly close relative.”

Grass carp in the United States are highly regulated to prevent them from becoming one more invasive species. To the best of my knowledge, they cannot be used in much of the U.S. unless they are certified as disease free and sterile. Sterile grass carp are known as “triploids” because they have an extra chromosome that is created when the fish eggs are subjected to a temperature or pressure shock. Fish are verified sterile by collecting and testing a blood sample. Triploid fish have slightly larger blood cells and can be differentiated from diploid (fertile) fish by this characteristic.

Grass carp are not legal in some jurisdictions. Many jurisdictions require permits before you can purchase grass carp, and they can only be purchased from certified dealers. There may be other restrictions, like making sure they can’t escape. It is different in all three states where I operate. Here in West Virginia, any dealer selling in West Virginia must have a state permit that allows them to sell grass carp. It is not incumbent on the pond owner to obtain the permit. In Virginia, all grass carp can only be purchased with a permit. After applying for the permit, a copy is sent to your supplier and you receive a copy. In North Carolina I generally have not needed a permit because they are only required when stocked in very large numbers and in certain bodies of water, especially if there is threat of escape into public waters.

So, before trying to purchase grass carp, check with your local dealer or your state’s natural resources offices.

Grass carp should not be confused with the invasive bighead and Asian carp that cause so many problems in the Midwest. Grass carp also do not eat other fish. They do not eat fish eggs. In most cases they will not eat your water lilies. They have a preferred menu. A link to some of their preferences is at the end of this article.

How many grass carp and what size?

It is recommended that new grass carp be of a size that predators, like largemouth bass and muskellunge cannot easily eat. Most suppliers provide them in the 8-10 and 10-12 inch range. Grass carp typically sell for about $1.00 - $1.50 per inch here in the mid-Atlantic area.

Grass carp grow extremely fast. I don’t want to gross anybody out, so I won’t show what the insides of a mature grass carp looks like. They really don’t have a stomach. Instead, they have a “short gut” which is actually extremely long. When a 30-inch grass carp is opened, it looks like there is a 10-foot long green sausage folded into the body cavity.

The pond size of less than 0.05 acres as I mentioned above received four grass carp for several reasons. One was the heavy infestation per surface area. Second, is that I expect I will have to replace them regularly because of the frequent visits by alligators.

The general rule is to add 8 to 15 grass carp per acre in a heavily infested pond, similar to what the pond described above looks like. Links at the end of this article will provide more information. Different states have different recommendations.

In my 0.7 acre West Virginia pond I keep just two grass carp and none in my ⅓ acre pond. The ponds are weed free, but they weren’t always that way.

An 8-inch grass carp stocked in April or May will typically be about 18 inches by the end of August. By the time they are more than about 24 inches they become less effective and should be replaced. I recommend replacing them with an appropriate number to just barely maintain your pond.

Adding too many grass carp can be a problem. They are very difficult to remove, especially in larger ponds that cannot be drained down. After they reach about 18-24 inches, they get lazy. If you are feeding your pond with fish food pellets, the grass carp swoop in and open their mouths like big vacuum cleaners. Each one can suck up a half pound of pellets pretty quickly.

Grass carp become very wary of any dangers extremely fast. They are skittish.

They can be removed with a seine if you can get them into a small area. However, when they get to 24-36 inches they can be pretty powerful. They can also jump very well. They are relatives of the bighead and Asian carp that have invaded the rivers in the Midwest that regularly injure boaters by jumping out of the water and into boats.

One of the most effective ways of removing them is finding a good archer with a bow that includes a reel and arrows on a tether. You will only really get one chance at them before they get shy of seeing a human figure. Rifles and shotguns are generally not effective because the projectile loses nearly all of its energy within the first inch or so of water. Rifle bullets also ricochet very easily off water causing other dangers.

I’ve been fairly successful removing them when the feeder goes off and they come in for dinner. They look like big silver torpedoes coming through the water. Using about a 2/0 or 4/0 circle hook embedded inside of about a ¾ to 1 inch diameter dough ball made from store bought sandwich bread can be fairly effective. You need heavy tackle, at least 12 lb., line and a good sturdy rod and reel. When you see the torpedo-like fuselage coming, toss the dough ball in its path. Hopefully it will grab it, and using a circle hook it should set the hook with its own momentum. If you hook it and it gets loose, you will probably have to wait a couple of months before you will see it again.

Can you eat grass carp?

Lastly, I frequently get asked if grass carp can be eaten. It’s a white, flaky meat, but has many bones that make it hard to process. Some people like it, others don’t.

Here is a note from Wikipedia about eating different carp:

Bighead carp is enjoyed in many parts of the world, but it has not become a popular foodfish in North America. Acceptance there has been hindered in part by the name "carp", and its association with the common carp which is not a generally favored foodfish in North America. The flesh of the bighead carp is white and firm, different from that of the common carp, which is darker and richer. Bighead carp flesh does share one unfortunate similarity with common carp flesh – both have intramuscular bones within the filet. However, bighead carp captured from the wild in the United States tend to be much larger than common carp, so the intramuscular bones are also larger and thus less problematic.

● Common carp, breaded and fried, is part of traditional Christmas Eve dinner in Poland and in the Czech Republic. In pond based water agriculture it is treated as most prominent food fish.

● Crucian carp is considered the best-tasting pan fish in Poland. It is known as karaś, and is served traditionally with sour cream (karasie w śmietanie).^[51] In Russia, this particular species is called Золотой карась meaning "golden crucian", and is one of the fish used in a borscht recipe called borshch s karasej^[52] (Russian: Борщ с карасе́й)or borshch s karasyami Russian: Борщ с карася́ми).

● Mud carp, due to the low cost of production, is mainly consumed by the poor, locally; it is mostly sold alive, but can be dried and salted.^[53] The fish is sometimes canned or processed as fish cakes, fish balls, ^[54] or dumplings. They can be found for retail sale within China.^[55]

● Chinese mud carp is an important food fish in Guangdong Province. It is also cultured in this area and Taiwan. Cantonese and Shunde cuisines often use this fish to make fish balls and dumplings. It can be used with douchi or Chinese fermented black beans in a dish called fried dace with salted black beans. It can be served cooked with vegetables such as Chinese cabbage.

● Fisherman's soup

● Kuai

● Taramosalata

● Masgouf, a popular Iraqi dish consisting of seasoned, grilled carp

● Gefilte fish, an Ashkenazi Jewish dish made from a poached mixture of ground deboned fish, primarily carp, whitefish, and pike

With this being said, I’m not a fan of grass carp. For those Pond Boss members who know of me, I am kind of the Bizarre Foods Guy of Pond Boss. The flesh is incredible. It looks like the best of the best fish flesh you can find. Firm and flakey. Properly prepared the bones can be removed, or in certain recipes the bones dissolve.

I’ve tried it deep fried, baked, grilled and smoked. I’ve marinated it. To me it has a sweet, almost perfumy taste which is not offensive, but I just don’t care for it. I’ve never tried it pickled.

Regards,

“Catmandoo” Ken Grymala

High View, West Virginia.

Links to more information about Grass Carp:

Wikipedia Cyprinidae

Wikipedia Grass Carp

Triploid Grass Carp Information

Aquatic Plant Identification

Aquatic Plant Management

Controlling Aquatic Vegetation with Grass Carp

Moderators' Corner

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