Grass Carp for Aquatic Weed Control

Herbivorous fish, the grass carp, sometimes call the white amur (Ctenopharyngodon idella) is the most effective biological method to control aquatic vegetation.

The white amur originated from the Amur river in China from which it received its name.  Grass carp are related to the common carp, but they look very different.  They are a much more slender fish and have a silvery color.  Their mouth is located at the front of the head, rather than down turned or sucker-like as in the common carp.

Grass carp will not reproduce in ponds and lakes since they need large, fast-flowing rivers for reproduction.  The young grass carp will feed on small crustaceans and insect, but as they grow larger shift their diet to plant material.  They prefer some plants over others, but will consume most species of floating and submersed plants.  They will pull out and feed on some of the immersed plants, but will not be able to control them. 

Grass carp have voracious appetites and grow rapidly.  They will eat 10 times their body weight a day and will gain 5 to 10 pounds in one year.  Researchers say that grass carp can reach weights of more than 70 pounds in this country.  Once the vegetation is controlled, their growth rates will level off also.  Contrary to belief, they can be caught on hook and line, and are exceptionally fine eating.

Suggested stocking rates for grass carp are from 10 to 20 per acre.  Stock 10 per acre for general maintenance, 15-20 per acre for 1/2 to completely covered ponds.  Control is achieved within one year at these stocking levels.  At half these levels, control may take up to two years.  The initial stocking should be effective for several years since these are long-lived fish.  A few replacement fish can be stocked if aquatic infestation increases.

Grass carp are highly mobile and they will rapidly leave a pond or lake during periods of heavy flow over the spillway.  Use of a mesh fence across the spillway can prevent loss of these fish.

Some states have restrictions regarding the use of grass carp.  Triploid carp are available for clients in states where such restrictions apply.