Abstract A 19-month study of effects of high density populations of grass carp, Ctenopharyngodon idella, and carp, Cyprinus carpio, on the reproduction and growth of bluegill, Lepomis macrochirus, and largemouth bass, Micropterus salmoides, was conducted in nine weed-free (0.1-hectare) ponds. Bluegill and largemouth bass were stocked at rates of 375 and 25 per pond, respectively. Three of the ponds were used as a control, three were stocked with 10 grass carp, and three were stocked with 10 carp. Benthic organisms and water quality were monitored. After two growing seasons, bluegill standing crop was significantly lower (P < 0.1) in both the grass carp and carp ponds. Bluegill standing crop was reduced by 52% in combination with grass carp and 67% in combination with carp. There were no significant differences in the standing crop of largemouth bass.