Sex differentiation and serum levels of sex steroids in meagre (Argyrosomus regius).

In the present study, serum levels of estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT) were monitored, in Argyrosomus regius, during both the sex differentiation and the first spawning season. Serum steroids levels and gonadal histology allowed us to define the sexual cycle of A. regius which is widespread over the Mediterranean Sea, although not very common around Italy and Greece. Results suggest that this species remains sexually undifferentiated until near the end of 9 months of age, there is a certain age (6 months) at which sexual differentiation becomes histologically recognizable. Gonadal differentiation in females occurs at an earlier age than in males. During the sex differentiating period in both sexes, GSI was low and unchanged while it significantly increased during the first spawning season. Serum levels of E2 during sex differentiation were low in both sexes, and significantly increased only in females at the end of this period. In male, during sex differentiation T levels were high and decreased during the following months. Serum 11-KT levels remained low and unchanged during sex differentiation, and increased during the first spawning season. In females the serum levels of T and 11-KT were lower with respect to estradiol levels. In conclusion the meagre is a gonochoristic species, which attains puberty at 2 and 3 years of age for males and females, respectively. Results suggest that in male T and 11-KT would have different roles in the regulation of testicular maturation. 11-KT could be involved in spermatogenesis and spermiation, while T in the sex differentiation. In female the estradiol is the major steroid involved in the oocyte maturation.