The external distance between the cleithrum bones was used to estimate the sizes of grass carp (Ctenopharyngodon idella) that could be ingested by Florida largemouth bass (Micropterus salmoides floridanus). The equations for mouth width vs. total length (TL) of largemouth bass were: Mouth (mm): 0.0968 (mm TL) for bass <200 mm TL (r2= 0.89); and mouth (mm) = −11.102 + 0.1567 (mm TL) for bass >200 mm (r2= 0.95). The equation for body depth vs. total length of grass carp was: depth (mm) = 0.629 + 0.204 (mm TL), r2= 0.98. Five thousand grass carp fingerlings were stocked in a 0.81-hectare vegetated pond. Initial predation was high in the sportfish pond, as only one grass carp was recovered at termination. Stocking of grass carp >450 mm is necessary to totally eliminate the possibility of piscivorous predation in lakes with established Florida largemouth bass populations.