TETRAPLOID INDUCTION WITH MITOSIS-I INHIBITION AND CELL-FUSION IN THE PACIFIC OYSTER (CRASSOSTREA-GIGAS THUNBERG)

Tetraploid induction was attempted in the Pacific oyster, Crassostrea gigas (Thunberg), with mitosis I inhibition and cell fusion. Mitosis I was blocked with heat shocks (35-40-degrees-C, for 2-23 min), producing up to 45% tetraploid embryos. Zygote-zygote fusion was successfully obtained with polyethylene glycol (PEG), without producing significant levels of tetraploidy. Sperm fusion was also tested, but the PEG treatment used in this study didn't lead to the fusion of sperm cells. On the other hand, PEG-induced blastomere fusion produced significant levels of tetraploids (up to 30%). There was no evidence that the tetraploid embryos produced in this study survived beyond D-stage. The poor viability of tetraploids produced in this study was probably caused by disruptions of the polar lobe formation by heat shock and cell fusion treatments.