Gilthead seabream, Sparus aurata, is a characteristic fish of south-atlantic and mediterranean coast of Europe and represents one of the most important species for Aquaculture in this region. As in other fish, successfull farming of sparids requires full understanding of endocrine influences on reproduction and sex reversion process, in order to either produce larvae all-year-round or to prevent undesired gonadal growth or male to female ratio. Gonadal steroid hormones, and estrogens particularly, seems to be implicated in sex differentiation and sex reversion, probably acting at the brain-pituitary levels. The proposed project is directed to obtain the molecular tools for investigating the expression of estradiol receptors in the brain and the pituitary of gilthead seabream and to determine the neuroendocrine circuits involving estradiol receptors and implicated in gonadotropin release. The results obtained will lead to a better understanding of the influence of estradiol on the process of maturation and sex reversion. Moreover, the results will provide basis to identify problems in other species and to develop methods allowing better control of spawning and sex reversion under farming conditions.