Abstract
The present study was conducted to investigate whether the equilibration steps (three or five steps), whale follicular fluid (WFF) addition and type of sugars (sucrose or trehalose) were effective for the viability and in vitro maturation (IVM) of vitrified immature oocytes in three baleen whales (sei, Bryde's and common minke whales). We also performed ultrastructural observation of vitrified and IVM oocytes. The viability of the five-step group (89.1%) was significantly higher than that of the three-step group (68.3%) in Bryde's whales, but the IVM rate of the five-step group (17.8%) was significantly lower than that of the three-step group (32.0%) in sei whales. In sei whales, the viability was significantly higher in the WFF addition group (90.6%) than the fetal calf serum (FCS) group (75.7%), but the IVM rates were not significantly different between the WFF and FCS group for either sei or Bryde's whales. The viability and maturation rate in the trehalose addition group were not significantly different from those in the sucrose addition group in both sei and Bryde's whales. Additionally, the trehalose group tended to exhibit a lower level of damage to cumulus cell projection and mitochondria than did the sucrose group in both sei and Bryde's whales. The tested step number of cryoprotectant equilibration, WFF addition and type of sugars did not improve the maturation rate of vitrified baleen whale oocytes. However, the present study showed that immature oocytes derived from three baleen whales in the western-North Pacific could be vitrified and matured in vitro at about 30% levels.
