Grass Carp

Introducing animals and plants that eat or compete with waterweeds represents another control method. Herbivorous animals (those that eat plants) include a wide variety of insects, snails, crayfish, tadpoles, turtles, fish, ducks, geese, and swans which can be stocked in ponds to consume water weeds.

Of these, the triploid (sterile fish with 50% more chromosomes than normal) Chinese grass carp (Ctenopharyngodon idella) is a weed-eating fish that can be stocked in ponds to provide effective, economical weed control for some rooted water weeds and filamentous algae. The recommended stocking rate is about 12 fish (9-12 inches in length) per surface acre. Ponds with very dense weeds may require more fish. Most state require a permit from the state fish and game agency to import and stock these non-native fish. In Virginia, questions about grass carp permits should be directed to Mrs. Frances Anderson, Virginia Department of Wildlife and Inland Fisheries at Phone: 804/367-1000

The major problem with introducing herbivorous animals into ponds for water weed control is that their body wastes act as fertilizers and stimulate weed growth. Herbivorous animals, by recycling nutrients, may do more harm than good. Many different types of aquatic plant compete with water weeds for space, light, nutrients, and other critical factors. Therefore, it is sometimes possible to discourage the growth of nuisance water weeds by planting beneficial aquatic plants. Some biological control agents are more harmful than beneficial.

Check with county extension agent before introducing animals or plants into your pond. Please note that the release of exotic (nonnative) animals or plants into Virginia without specific authorization is strictly forbidden by state laws.

Click here to download a .pdf version of the VDGIF Exotic Species Application/Permit To Import Certified Triploid Grass Carp For Aquatic Vegetaion Control in Private Ponds. (You will need a copy of the Adobe Reader to view this file.  If you do not have a copy, visit the Adobe website to download a free copy.)