Physiological control of reproduction in Female winter flounder (Pseudopleuronectes americanus Walbaum)

Vitellogenesis in Pseudopleuronectes americanus Walbaum involves a transfer of yolk material synthesised by the liver into the oocytes in the gonad. The hormones controlling these processes were studied. Hormones which can induce maturation and/or ovulation of oocytes were identified. -- The gonadal lipid accumulation during winter starvation is not accounted for by the decrease in the concentration of liver lipid. Vitellogenesis must consist of three phases; mobilization of lipid and other energy reserves into the circulation, synthesis of yolk proteins by the liver, and uptake of yolk into oocytes. -- Hypophysectomy suppressed both liver synthesis and oocyte uptake of yolk protein. Injection of estradiol-benzoate restores the liver synthesis of yolk, resulting in accumulation of yolk proteins in serum because none is incorporated by the gonad. A glycoprotein fraction from Hippoglossoides platessoides Fabricius pituitaries, which is capable of stimulating ovulation, did not promote uptake into the gonads of the estradiol induced serum yolk but a non-glycoprotein fraction from these pituitaries with a molecular weight of 25000 to 35000 stimulated yolk incorporation. -- 17α-Hydroxy progesterone and 20β-dihydro-17α-Hydroxy progesterone were identified in plasma samples which had induced oocyte maturation in vitro bioassay, using a double isotope derivative assay. Cortisol, cortisone, deoxycorticosterone, 11-ketotestosterone and progesterone were identified in various plasma samples but not correlated to oocyte maturation. -- Cortisone, deoxycorticosterone, 17α-hydroxy progesterone or 20β dihydro-17α-hydroxy progesterone induced maturation of oocytes incubated in plasma from male fish but appeared to have no conclusive effect upon oocytes incubated in artificial media. Injection of these steroids, estradiol-benzoate or testosterone into hypophysectomized fish did not induce oocyte maturation or ovulation. -- A salmon gonadotropic preparation (SG-G100) or extracts of P. americanus pituitaries induced some oocyte maturation in vitro. Both a glycoprotein preparation from H. platessoides pituitaries and SG-G100 induced oocyte maturation and ovulation when injected into hypophysectomized fish