Developmental capacity of non-nucleated embryos of coho salmon, Oncorhynchus kisutch, induced by γ-irradiation

The effects of γ-rays on chromosomes and nuclei were examined by observing embryos of coho salmon, Oncorhynchus kisutch, produced using either sperm or eggs that had been exposed to γ-irradiation. These embryos had smaller nuclei than normal control embryos, and half of the normal chromosome number, suggesting that the genomic DNA of the gametes had been inactivated by γ-irradiation. Furthermore, non-nucleated embryos were produced using both sperm and eggs that had been γ-irradiated under the same conditions. In spite of the fact that the fertilized eggs lacked Feulgen-positive material, cleavage was observed in the embryos, and some developed to the blastula stage. These results suggest that the early stages of embryogenesis of fertilized fish eggs may be influenced by the cytoplasm rather than the nucleus.