Characterization of genes related to advanced gonadal growth in prepubertal European sea bass females

Several studies suggest that body weight in teleost during critical periods affects the proportion of fish that reach maturation in a given reproductive season. Although there is a large variation in the age of maturity, this trait depends on genetic, physiological and environmental factors that contribute to gonadal growth. While interactions between growth and reproductive competence in male fish have been reported, much is still to be resolved in females. In the sea bass a substantial proportion of males mature precociously during the first year of life suggesting that it is only allowed in those fish which have reached a certain threshold of development or accumulated enough lipid reserves. Precocious males, which are usually larger in size, exhibit a significant increase in 11-KT presumably induced by Fsh that is able to block amh expression, a meiosis inhibiting factor, thus evoking spermatogenesis progression. Little is known about the oocyte growth in prepubertal female sea bass and its relationships with body growth; however it has been reported that advanced puberty can also affect captivereared females. Recently, we have monitored the growth history of female sea bass and the degree of advancement in oocyte development during the first two years of life. Some body indexes and circulating vitellogenin served as markers of advanced ovarian growth. Over the second year of age, females could be divided into four distinct groups: females that remained at perinucleolar stage, females with oocytes in varying degrees of cortical alveoli incorporation and no lipid droplets, females with oocytes in secondary growth including oocytes in varying degrees of lipid droplet incorporation and no yolked droplets and females with oocytes with both lipid and yolked droplets inside. Consequently, our objective is to determine changes in ovarian gene influencing the rate of oocyte development in this aquaculture finfish species.