Ctenopharyngodon idella (Grass Carp) is a large (to 790 mm) herbivorous fish, native to lowland rivers of China and the Amur basin of the former USSR. This fish has been introduced worldwide for aquaculture and aquatic weed control and is now established in the wild in Africa, Russia, Japan, Mexico, Serbia and other countries. In the United States, it was introduced for weed control in aquaculture ponds, and was not expected to breed. However, it established populations in the Mississippi basin. However, since this fish was useful for weed control, sterile triploid fishes were widely introduced. However, triploid fishes can undergo reversion to fertile status, limiting their introduction because of risks to submerged aquatic vegetation. Most of the Grass Carp caught in the East and West Coast estuaries of the US are sterile triploids, but reproducing populations may occur on the Gulf Coast, and have been confirmed in the Great Lakes.