Isozyme expression in bighead carp, silver carp and their reciprocal hybrids.
Samples of the University's populations of bighead carp (Aristichthys nobilis), silver carp (Hypophthalmichthys molitrix) and their reciprocal hybrids were surveyed for isozyme variability at 23 loci. Allelic variation at loci coding for alcohol dehydrogenase, creatine kinase, lactate dehydrogenase, malate dehydrogenase and superoxide dismutase was used to differentiate the 2 species. Reciprocal hybrids could not be distinguished electrophoretically. Isozyme banding patterns indicated that the hybrids were diploid. The hybrids were fertile, and they produced large numbers of F2 progeny. The bighead carp population had 4% of its loci polymorphic, whereas the silver carp were polymorphic at 17% of loci. The bighead carp evaluated in this study have a degree of homozygosity that is probably related to the hatchery breeding procedures used.