Natural sex change in mature protogynous orange-spotted grouper (Epinephelus coioides): gonadal restructuring, sex hormone shifts and gene profiles.

Sexual patterns of teleosts are extremely diverse and include both gonochorism and hermaphroditism. As a protogynous hermaphroditic fish, all orange-spotted groupers (Epinephelus coioides) develop directly into females, and some individuals change sex to become functional males later in life. This study investigated gonadal restructuring, shifts in sex hormone levels and gene profiles of cultured mature female groupers during the first (main) breeding season of 2019 in Huizhou, China (22 degrees 42 ' 02.6 " N, 114 degrees 32 ' 10.1 " E). Analysis of gonadal restructuring revealed that females with pre-vitellogenic ovaries underwent vitellogenesis, spawning and regression and then returned to the pre-vitellogenic stage in the late breeding season, at which point some changed sex to become malesviathe intersex gonad stage. A significant decrease in the level of serum 17 beta-estradiol (E2) was observed during ovary regression but not during sex change, whereas serum 11-ketotestosterone (11-KT) concentrations increased significantly during sex change with the highest concentration in newly developed males. Consistent with serum hormone changes, a significant decrease incyp19a1aexpression was observed during ovary regression but not during sex change, whereas the expression ofcyp11c1andhsd11b2increased significantly during sex change. Interestingly,hsd11b2but notcyp11c1was significantly upregulated from the pre-vitellogenic ovary stage to the early intersex gonad stage. These results suggest that a decrease in serum E2 concentration and downregulation ofcyp19a1aexpression are not necessary to trigger the female-to-male transformation, whereas increased 11-KT concentration and upregulation ofhsd11b2expression may be key events for the initiation of sex change in the orange-spotted grouper.