Grass Carp are native to Malaysia. They were imported by the U. S. Fish and Wildlife Service in 1963 for research in aquatic plant control. Amur are native to the river systems of northern China, and southern Siberia.
Grass Carp or White Amur can effectively control aquatic vegetation in ponds and lakes. Yearly chemical weed control with a typical herbicide like Diquat can cost $200.00 per acre multiplied by the average depth. If the average depth is 5 feet that is a $1000.00 expenditure for chemicals alone (the cost of application must be added to that). A additional applications may be necessary.
Grass carp are very economical even at $14.00 each or more. Stocked at 10 per acre (the stocking rate will vary depending upon your aquatic environment) You have an investment of $140.00 per acre that will control weed growth (not algae) for 6 to 8 years. The fish will live longer than that, but the larger fish do not control vegetation like the younger actively growing ones.
The following comments are from the discussion section of A Comparison of Fish Populations Before and After Extensive Grass Carp Stocking by William M. Bailey Arkansas game and Fish Commission Little Rock, Arkansas 72201, Reprinted from Transactions of the American Fisheries Society, Vol. 107, No. 1 January 1978 Grass Carp and Standing Game Fish Populations.
. . . . And an overall view of the data suggests that grass carp have had practically no effect upon total standing crop, shad biomass, numbers of catchable largemouth bass, sunfish, and crappie, or numbers of young-of-the-year sunfish and bass. The plant removal by grass carp did appear to improve the condition factor of largemouth bass, bluegill, and redear sunfish. . . . . . . . One effect of grass carp upon the environment that can be predicted with certainty is the removal of submersed plants. In Arkansas, this is considered beneficial. It renders the water more accessible, more suitable for fishing, for swimming, for pumping, for boating, and for fish population manipulation.
It is this author's opinion that submersed aquatic weed control with grass carp is far superior to chemical control, mechanical control, or no control. Long term chemical effects upon fish populations are either unknown or definitely detrimental and expensive. Mechanical control is temporary and expensive. The alternative which has the least effect upon fish populations and other wildlife and costs nothing directly, is no control. However, a weed-choked lake has little fisherman appeal, and if the ultimate goal is to satisfy the greatest number of fishermen, have efficient water flow, boating, or navigation, no control is not a viable alternative. Our lakes are managed for the benefit of the fishery and in these managed lakes where submersed weed control is desired the grass carp is an effective and desirable tool.
|Number of Amur|
|New pond or very slight weed problem||5|
|Moderate weed problem (10 to 20% coverage)||10 to 15|
|Severe Weed Problem||15 to 20+|
From: Utilizing Triploid Grass Carp For Aquatic Vegetation Control in Ponds Forrest Wynne, Area Extension Specialist for Aquaculture, Kentucky State University Cooperative Extension Program, P.O. Box 3327, West Somerset, KY 42564-3327 (606) 679-2090
Pennsylvania requires that the pond owner have a permit before stocking amur. Some states do not allow grass carp at all. Most states require that they be certified "triploid." This means that the fish have a split chromosome so the sex cells cannot combine for fertilization. Triploids are produced by temperature shocking the developing eggs. This kills 90% of them and the survivors are effectively sterile. Verification of the Triploid condition requires expensive equipment, is labor intensive and time consuming. This process is the reason for the high cost of these fish.
Grass Carp can reach a size of at least 35 to 40 lb. in ponds in mid-western states. Their life expectancy is 8 to 12 years. Some do live longer, but the larger they get the less they eat so they are less effective in plant control. Older fish give the impression of being related to submarines. They can reach 4 feet and 100+ pounds in their native rivers. Amur are usually stocked at 10 to 12 inches. An 8 inch minimum is a required to keep them from becoming expensive bass feed!
Once grass carp have been stocked it is too late to change your mind. Amur are very active and alert. They avoid traps and seines.
Grass carp prefer some plants over others just as some people don't like spinach or broccoli. Plants that are not preferred will be consumed only after the favorites are gone. Grass carp DO NOT control algae, duckweed, and watermeal.
|Coontail (Ceratophyllum)||Pondweeds (Potamogeton)|
|Button bush||Southern watergrass|
|* Duck weeds||Waterhyacinth|
|** Filamentous algae||* Watermeal|
|Fragrant waterlily||Water pennywort|
|Planktonic algae||White waterlily|
* Grass Carp will consume duck weeds and water meal but they may not be able to control the populations of these plants.
** Filamentous algae may be controlled by grass carp 2-4 inches in length in ponds without predators. Larger fish may consume filamentous algae but it is not a preferred food and effective control may be unpredictable.
Source: Utilizing Triploid Grass Carp for Aquatic Vegetation Control in Ponds Forrest Wynne, Area Extension Specialist for Aquaculture, Kentucky State University Cooperative Extension Program, P.O. Box 3327, West Somerset, KY 42564-3327 (606) 679-2090.