The females of anadromous sturgeon species migrate to rivers from the sea with their germ cells still immature. Their oocytes are located in the ovaries. If river flow is not regulated, some fish such as vernal H. huso, A. gueldenstaedti, A. persicus, and A. stellatus migrate into rivers with their gonads at the completed stage IV of maturity; their ovaries contain large fully grown oocytes. These female spawn during the same year. Other fish enter the rivers with gonads at stages III–IV and incomplete stage IV of maturity. These fish, which include the hiemal summer-migrating A. gueldenstaedti and the hiemal H. huso and A. stellatus, nest in holes for several months and spawn only during the following year.
KeywordsOocyte Maturation Germinal Vesicle Coelomic Fluid Cortical Granule Gonadotropic Hormone
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