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

Campbell, Christopher Moger (1975) Physiological control of reproduction in Female winter flounder (Pseudopleuronectes americanus Walbaum). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

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.

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