Triploid grass carp (Ctenopharyngodon idella) (N = 125, 50.8-98.6 cm total length [TL]) were implanted with radio tags and released into 5 reservoirs (25 fish each in Dunlap, McQueeney, Placid, H4, and H5) on the Guadalupe River, Texas. These fish were located periodically to determine specific movement patterns in and among the series of riverine reservoirs and the Guadalupe River system to provide an evaluation of their use and safety as an aquatic vegetation control tool. All grass carp survived tag placement surgery and stocking into assigned reservoirs. However, beginning 7 months after release, stationary radio tags (no longer implanted in a fish and lying on the bottom due to tag loss and fish mortality) were located. Ultimately, 60 stationary tags were recovered and placed into other grass carp for release where each tag was found. Grass carp emigration from home reservoirs occurred throughout the study. Emigration was always observed in a downstream direction. Grass carp emigrated from these reservoirs at a rate of approximately 3.5% each 6 months during the first 18 months of study, which had low river-flow conditions. During high river-flow conditions, grass carp emigrated from these reservoirs at a rate of approximately 59% in 6 months. Seventy grass carp moved past 1-10 dams, emigrating a maximum 1-way distance of 325 km. Due to observed grass carp emigration, they are not recommended for vegetation control efforts in similar riverine aquatic systems.
