The reproductive viability of grass carp (Ctenopharyngodon idella) in the western basin of Lake Erie

Grass carp, Ctenopharyngodon idella, one of the Asian carps, was first introduced into the United States in 1963 as a biocontrol agent to assist in the control of aquatic plants in ponds and lakes. Intentional biocontrol releases, however, had undesirable outcomes and resulted in fish that escaped and spread to other lakes and rivers. While the overall extent of their impact is not fully known, grass carp pose a significant risk to native biota because of their invasive qualities. Although a program exists to prevent the release of fertile grass carp which is prohibited in all of the Great Lakes states, there has been recent evidence of natural reproduction in the Sandusky River and a few reproductively viable individuals captured in Lake Erie proper. While previous published studies have documented reproduction, the sample sizes were comparatively low (n = 9) and limited to the Sandusky River tributary. Thus, prior reports likely do not represent the overall reproductive dynamics of grass carp in Lake Erie. As such, the reproductive status (ploidy; diploid vs. triploid) of feral populations in Lake Erie proper is largely unknown. Here, we assess the reproductive status of grass carp captured in western Lake Erie over a three-year period to inform the risk of future population growth. Ploidy from sixty individuals was determined in our sampling and 86.7% of grass carp were reproductively viable (diploid). Our results enable management to better understand the reproductive potential of feral grass carps in Lake Erie and assist with management of this invasive carp.