In vitro oocyte maturation in the zebra fish, Brachydanio rerio, and the fertilization and development of the mature egg.

The in vitro maturation process of zebra fish oocytes was investigated. When incubated with medium EM-199 containing 0.5 microgram/ml of 17 alpha-hydroxyprogesterone in an incubator with 80% O, 25 degrees C, the germinal vesicles of the oocytes in stage IV migrated from middle between the center and the periphery to the periphery in 40 min, and the oocytes went into stage V 30 min later, undergoing germinal vesicle breakdown (GVBD) with a GVBD% of 59%. Two hours were needed for such oocytes to complete their final maturation. The mature eggs cannot come off the follicle layer surrounding them naturally (ovulation). By removing the follicle and adding active sperm for insemination, we can cause the mature eggs to become fertilized. The chorion elevated and blastoderm formed on the animal pole. The cleavage and development of the fertilized eggs followed are the same as naturally matured fertilized eggs. Using blastula as the criterion for a successful fertilization of the in vitro maturated egg, the fertilization rate is 78%. This is the first report on the successful oocyte final maturation in vitro in zebra fish. The establishment of an oocyte in vitro maturation technique has given grounds for the further investigation on the transfer of foreign genes in the germinal vesicles of the oocytes.