Seasonal changes of serum sex steroids concentration and aromatase activity of gonad and brain in red-spotted grouper (Epinephelus akaara)

Levels of serum sex steroids (estradiol-17β, E2; testosterone, T; 11-ketotestosterone, 11-KT) in male, female and natural sex-reversing red-spotted grouper (Epinephelus akaara), and aromatase activity of gonad and brain in both male and female were investigated throughout an annually reproductive cycle. In females, serum E2 and T peaked during vitellogenesis, but in males and natural sex-reversing fish, 11-KT, T and E2 reached peak during spermatogenesis. In addition, in females, serum 11-KT levels (monthly means: 0.32 ± 0.03 ng/ml) which were very low did not significantly fluctuate during the annual reproductive cycle. In breeding season, females displayed higher E2 levels than males and sex-reversing fish, while males and sex-reversing fish showed higher 11-KT levels and, to a lesser extent, higher T levels than females. Furthermore, the changing pattern of sex steroids in males was similar to that in natural sex-reversing fish, and a second peak of serum androgens 11-KT and T appeared in December both in male and natural sex-reversing fish; significantly higher serum 11-KT levels were observed in natural sex-reversing fish than that in females from December to April. In females, but not in males, aromatase activity of brain and gonad demonstrated significantly seasonal changes (exhibiting a peak in breeding season); moreover, aromatase activity in females was higher than that in males. Furthermore, significantly lower aromatase activity in testis was observed in breeding season, in contrast to that in ovary. Taken together, the present findings indicated that changes of serum sex steroids levels and aromatase activity in red-spotted grouper were closely associated with sex inversion. In addition, the present results also suggested that sex inversion in red-spotted grouper peaked mainly from December to March.