Grass Carp, also called white amur, are a biological control for aquatic vegetation. Unlike common carp, Grass carp will not spawn in ponds or muddy the water. Native to the Amur river in China, grass carp are strict herbivores using specialized teeth in the back of their throat to graze submerged plants from the top down. Grass carp require flowing water of large rivers to spawn and therefore cannot reproduce in ponds. Grass carp also grow to large sizes, are fun to catch and good to eat.
Grass carp were imported in 1963 by the USFWS for evaluation as an alternative to chemical control methods. Proving to be the most effective aquatic vegetation control, grass carp were made available to the public in 1973 for stocking private ponds. Because grass carp are an exotic species, concerns over their spread prompted many states to outlaw the stocking of diploid (fertile) grass carp in 1977.
This prompted J.M. Malone and Son, Inc. to develop a method for the production of triploid (sterile) grass carp on a commercially viable scale. In 1983, the company successfully produced their first triploid grass carp and pioneered the use of the Coulter Counter and inspection protocol to rapidly identify, isolate and certify 100% triploid grass carp for sale. With the introduction of certified 100% Triploid Grass Carp many states allowed the sale and stocking of triploid (sterile) grass carp for aquatic vegetation control.
Like you and me, regular diploid grass carp have two chromosomes in every cell allowing the fish to produce viable eggs or sperm with 1 chromosome each. Triploid Grass carp have three chromosomes in each cell preventing them from producing viable eggs or sperm, making them functionally sterile. Triploid grass carp are produced by combining the eggs and sperm from diploid grass carp and then shocking the fertilized eggs with temperature, pressure or chemicals early in development. The shock causes the egg to retain a naturally occurring third set of chromosomes that would normally be discarded.
This process is often variable, therefore, to ensure only high ploidy groups of grass carp are stocked for production, J.M. Malone and Son, Inc. tests each group of grass carp fry before they are stocked into nursery ponds and each group of grass carp fingerlings before they are stocked into production ponds. Then, before triploid grass carp can be sold each fish must be individually blood tested to ensure it is triploid. Once each fish has been individually tested using a coulter counter, a USFWS inspector visits the farm and randomly retests 120 fish from each prospective shipment. If all of the 120 randomly selected fish are triploid a certificate is issued verifying that every fish in the prospective shipment is in fact a triploid. If even one diploid is found during the random inspection of the prospective shipment, no certificate is issued and every fish in the shipment must be individually retested. Before a certificate can be issued another 120 randomly selected fish must pass another USFWS inspection. Once an inspection is passed and a certificate is issued triploid grass carp may be shipped from the farm. To see this process follow this link to our slideshow.
As the World's Largest Producer of Certified 100% Triploid Grass Carp J.M. Malone and Son, Inc. operates a state of the art Triploid Grass Carp Blood Analysis Lab. With a full time staff of seven people our lab is capable of individually testing 1000 grass carp per hour and by volume has the lowest failure rate in the USFWS Triploid Grass Carp Ploidy Verification Program.
Pond owners may be required to purchase permits from their State before stocking Triploid Grass Carp in their pond. Due to the required blood testing and USFWS certification Triploid Grass Carp are more expensive than normal diploid grass carp.
As of January 1, 2023 diploid grass carp are only allowed for pond stocking in Alabama, Mississippi, Missouri, Iowa, and Nebraska. Triploid Grass Carp certified by the USFWS are required by Arkansas, Tennessee, Oklahoma, Texas, Louisiana, Florida, Georgia, North Carolina, Virginia, West Virginia, Pennsylvania, New Jersey, New York, Connecticut, Kentucky, Illinois, Indiana, Ohio, Colorado, Kansas, Arizona, New Mexico, Utah, Nevada, California, Oregon, Washington, Idaho, South Dakota and Wyoming. South Carolina only allows Triploid Grass Carp however USWFS certification is not required.
Please check your local laws regarding the purchase of Grass Carp for vegetation control in your pond. Many states require evaluations or permits before grass carp can be purchased. It is a federal offense to transport grass carp across state lines in violation of state law, so please be informed of your local laws.
Grass Carp should be stocked between October and April before vegetation is actively growing. Triploid grass carp purchased at this time of year are robust after completing a full growing season and dormant from cool water temperatures. This allows for improved handling and stocking, ultimately resulting in more effective vegetation control. Once water temperatures begin to rise in the spring the fish will emerge unscathed from their dormant state with a racing metabolism and a need to consume an abundance of aquatic vegetation. Triploid grass carp purchased and stocked during late spring and summer do not handle as well due to their high metabolism. Stocking triploid grass carp during this time period is often unsuccessful due to high water temperatures, low oxygen concentrations and dense aquatic vegetation resulting in poor aquatic vegetation control.
Grass carp prefer aquatic vegetation such as Duckweed, Chara, Naiad, Potamogeton, Eurasian Watermilfoil, Bladderwort, Hydrilla, Elodea, Coontail, Spikerush and Water Stargrass. Grass carp generally do not prefer filamentous algaes, watermeal, watersheild, spatterdock, waterlilly, arrowhead, water hyacinth and cattails. Plant preference is greatly linked to fish size. Smaller grass carp will readily eat filamentous algae and pithophora while larger grass carp do not prefer this species but will eventually eat it once they have eaten other available species. Emergent vegetation such as hyacinth and arrowhead are generally not preferred by grass carp, however once grass carp have reached large sizes they will eat these species.
Complete eradication of aquatic vegetation can be rapidly achieved by stocking 10 to 12 grass carp per surface acre. While eradication is sometimes preferred by some pond owners, it is normally not in the best interest of public water bodies. Aquatic vegetation can be managed rather than eradicated by using smaller periodic stockings of grass carp and monitoring the response of the aquatic vegetation to grazing, weather and water quality. Three to five fish per acre will generally manage aquatic vegetation in small ponds and lakes. Stocking 1 to 3 grass carp per vegetated surface acre every 3 to 5 years is becoming more popular with large public vegetation control projects. The growth of aquatic vegetation is influenced by weather, water quality and water levels. The level of control provided by grass carp is dependent on the size and age structure of the grass carp population and the growth rate of the aquatic vegetation. Modern aquatic vegetation management plans must continuously monitor these dynamic relationships to achieve the desired outcome.