Improvement on in vitro maturation, fertilization and development of minkewhale (Balaenoptera acutorostrata) oocytes

The aims of the present study were to improve in vitro maturation, fertiliz ation and subsequent development of minke whale oocytes. We investigated th e effects of different concentrations (0, 10 and 20%) of fetal whale serum (FWS) in maturation medium on nuclear maturation, morphological grade (A or B) of cumulus-oocyte complexes (COC) obtained from prepubertal and adult m inke whales. Grade A (greater than or equal to5 layers of cumulus cells) CO C collected from the adult whales and cultured in the medium with 20% FWS h ad a higher (P<0.05) maturation rate (31.8%) than those in the medium witho ut FWS (0%), Adding FWS to the maturation medium significantly (P<0.01) imp roved the proportion of oocytes at Metaphase II (M-II): without FWS (7.9%), with 10% (19.4%) and 20% (21.4%) FWS. However, sexual maturity of whales a nd COC grades were not significantly affected by M-II oocytes. When in vitr o fertilization of matured oocytes was performed in the presence of 20% FWS or 0.6% BSA in the fertilization medium, the proportions of sperm penetrat ion and two-pronuclei formation in matured oocytes were not significantly d ifferent. Grade A COC cultured in a culture medium supplemented with 10% FW S cleaved at a higher rate (15.4%, P<0.05) than did Grade A and B COCs cult ured in the medium without FWS (0%). Neither Grade A nor B COCs cleaved whe n the medium was without FWS. The proportions of cleaved oocytes increased (P<0.05) with FWS supplementation (6.9% and 8.1% for 10% FWS and 20% FWS, r espectively). Grade A COC was significantly (P<0.05) superior in its abilit y to cleave (14.5%) and develop to morula (4.2%) compared with that of the oocytes from Grade B COC (2.5% and 0%). Coculture with granulosa cells duri ng in vitro culture did not significantly affect cleavage and development t o the morula stage. These results indicate that FWS addition in the maturat ion medium improved the rate of in vitro maturation and cleavage after inse mination of minke whale oocytes. The BSA supplementation in fertilization m edium was as effective as FWS supplementation for in vitro fertilization of matured oocytes. In vitro embryo production beyond the morula stage of min ke whale oocytes could be possible, if Grade A COC was selected and culture d in the maturation medium supplemented with 10% or 20% FWS. (C) 2001 by El sevier Science Inc.