Ecological Risk Screening Summary - Grass Carp (diploid) (Ctenopharyngodon idella var. diploid) - High Risk

Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.

Ctenopharyngodon idella, Grass Carp, is a freshwater fish that is native to eastern Asia from the Amur River in eastern Russia to southern China. It is commonly used for aquaculture and as a biocontrol for aquatic vegetation. Spawning occurs in summer months with rising water levels and warmer water temperatures. The History of Invasiveness for C. idella is classified as High because this species has been introduced to over 80 countries worldwide with documented negative impacts. Established populations, i.e., those with natural reproduction, have been documented in North America (United States, Mexico), southeastern Europe, western and central Asia, and South Africa. In the United States, both triploid and diploid Grass Carp have been stocked or introduced in areas where evidence of natural reproduction has been documented including throughout the Mississippi River, western Lake Erie, and Colorado River drainages. Negative impacts associated with C. idella introductions are well documented in scientific literature and include the species’ ability to alter trophic structures, removal of aquatic vegetation, degradation of habitat, and spread of pathogens. The climate matching analysis for the contiguous United States indicates establishment concern for this species. High climate match was found throughout the Mississippi River drainage and within the Appalachian Range, Great Lakes, Southeast, Northern Plains, Southern Plains, and portions of the Intermountain West. The Certainty of Assessment for this ERSS is classified as High due to the abundant information available regarding the distribution, biology, and impacts of introductions documented in peer-reviewed literature. The Overall Risk Assessment Category for C. Idella in the contiguous United States is High.