Hybridization, androgenesis, and gynogenesis were studied as potential methods for creating nonreproducing populations of fish. Hybrids from crosses of female grass carp (Ctenopharyngodon idella) X male carp (Cyprinus carpio, Israeli mirrow variety) died during embryonic development. Hybrids of the reciprocal cross hatched and were stocked in ponds, but most died within 3 months. Dimensions of the nuclei of erythrocytes from hybrids indicated that survivors were polyploid. Androgenetic grass carp and gynogenetic carp were both observed in this reciprocal cross. Gynogenesis occurred in 3% of the eggs from grass carp fertilized with UV-irradiated milt from carp. Nuclear dimensions of androgenetic and gynogenetic fish suggested a diploid karyotype. The yield of 7,862 gynogenetic grass carp is evidence that this method might be practical for production of monosex fish for experimentation.