INVIABLE HYBRIDS OF CRASSOSTREA-VIRGINICA (GMELIN) WITH C-RIVULARIS (GOULD) AND C-GIGAS (THUNBERG)

Interspecific hybridization may provide important tools for selective breeding programs in oyster culture, especially for enhancement of dis ease resistance, and may have a bearing on debates concerning the intr oduction of non-native species. Factorial crosses of C. virginica with C. rivularis (C. arakiensis) and C. gigas were made, producing contro l and hybrid larvae. Larval survival and growth were documented. After several replicated experiments it became apparent that diploid hybrid s were inviable, and so triploid hybrids were also tested and found to be equally inviable. Feeding studies with hybrids were initiated to d etermine if lack of growth and viability were related to capture of fo od. Overall, hybrids of C. virginica with C. rivularis and C. gigas ca n be readily produced, but are inviable after 8-10 days and grow littl e. With regard to the species examined here, previous reports of succe ssful hybridization should be questioned. Introduction of C. gigas to the native range of C. virginica will not have direct genetic effects on C. virginica.