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Effects of Polyunsaturated Fatty Acids and Prostaglandins on Oocyte Maturation in a Marine Teleost, the European Sea Bass (Dicentrarchus labrax)¹

^a Instituto de Acuicultura (Consejo Superior de Investigaciones Científicas), Torre de la Sal, 12595 Castellón, Spain

ABSTRACT

The effects of the polyunsaturated fatty acids (PUFAs), arachidonic acid (AA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and prostaglandins (PGs) on oocyte maturation were investigated in a marine teleost, the sea bass (Dicentrarchus labrax). Follicle-enclosed postvitellogenic, preovulatory oocytes were cultured in vitro and maturation was verified by assessing volume increase, lipid droplet coalescence, yolk clarification, and germinal vesicle migration and breakdown. Human chorionic gonadotropin was administered as the maturation-inducing gonadotropin (GTH) and was capable of inducing maturation in a time- and dose-dependent manner. Free AA induced maturation in a dose- and time-dependent manner and enhanced GTH-induced maturation, while EPA, DHA, and oleic acid were ineffective. Maturation induced by GTH was significantly suppressed by a phospholipase A₂ blocker, suggesting that mobilization of AA was involved in GTH-induced maturation. Moreover, EPA and DHA exhibited a significant, dose-dependent attenuation of GTH-induced maturation. Maturation induced by GTH was inhibited in the presence of a cyclooxygenase inhibitor, indomethacin, and this inhibition was reversed by addition of AA, PGE₂, or PGF₂. PGE₂ and PGF₂ alone were both effective stimulators of maturation, while PGE₁ and PGE₃ were ineffective. The effect of PUFAs on oocyte maturation in vitro were corroborated with studies in vivo. Oocytes were obtained from females fed a commercial, PUFA-enriched diet (RD) and maturational behavior was compared with oocytes from females fed a natural diet (ND) with a higher EPA content and n-3:n-6 ratio. Although no significant difference was observed in the rate of spontaneous oocyte maturation, a higher percentage of GTH-induced maturation and lower percentage of atresia were observed in RD oocytes. Moreover, while basal PGE production from oocytes from both groups was the same, RD oocytes produced significantly higher levels of PGE in the presence of hCG. The results from this study provide evidence for the participation of AA metabolism in GTH-induced oocyte maturation, and suggest that other PUFAs and PGs may play important roles in the induction of maturation in a marine teleost.

FOOTNOTES

First decision: 4 April 2000.

¹ These studies were supported by a C.I.C.Y.T. grant (Mar 96-1859) to M.C., a grant from the European Union (AIR2-CT93-1005), a postdoctoral fellowship to L.A.S. from the Spanish Ministry of Science and Education, and a predoctoral fellowship from the regional government of Valencia, Spain (Generalitat Valenciana) to J.F.A.

² Correspondence: Silvia Zanuy, Instituto de Acuicultura de Torre de la Sal, Torre de la Sal, 12595 Ribera de Cabanes (Castellón), Spain. FAX: 34 964 319509; zanuy{at}iats.csic.es

³ Current address: Laboratorio de Acuicultura, Departamento de Ciencia Animal, Universidad Politécnica de Valencia, Camino de Vera, 14. 46071 Valencia, Spain.

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