Induction of precocious females in the protandrous barramundi (Lates calcarifer) through implants containing 17?-estradiol-effects on gonadal morphology, gene expression and DNA methylation of key sex genes

Sex control is vital for the efficient breeding of aquaculture species. Barramundi (Lates calcarifer) is a protandrous sequential hermaphrodite that naturally sex change from male to female over its lifespan. The induction of precocious female barramundi will permit breeding of males and females of the same-generation individuals in selective breeding programs, increasing the rates of genetic gain, while reducing infrastructure costs. Accordingly, the efficacy of two dosages of 17?-estradiol (E2) delivered via implants to induce the precocious female barramundi were evaluated. Six-month-old male barramundi (405 ? 50 g body weight (BW)) were given a single cholesterol-based pellet implant containing either 0 mg E2 kg-1 BW (untreated control), 4 mg E2 kg-1 BW (?low dose?), or 8 mg E2 kg- 1 BW (?high dose?). Changes in gonadal morphology and liver condition of implanted males, along with RT-qPCR and bisulfite amplicon sequencing to quantify expression profiles and DNA methylation of key male-female sex-related genes were then examined after 9 weeks post-implantation. Results showed that at 9 weeks post-implantation, in the ?high dose? E2 treatment group, 78% (7/9) of fish sex-changed completely to female, signified by gonads containing oocytes (20?30 ?m) and no observed residual sperm. Comparably, 44% (4/9) of fish in the ?low dose? E2 treatment group had sex-changed, while remaining fish showed complete testicular regression with gonads containing only undifferentiated germ cells. In the ?high dose? E2 treatment, upregulation of female-biased genes (cyp19a1a and foxl2) and downregulation of male-biased genes (dmrt1, cyp11b and esr1) were observed. Increased gene expression was accompanied by decreased DNA methylation in cyp19a1a, but no significant changes in DNA methylation of foxl2 or esr1 were observed. The success of artificially-induced sex change in barramundi provides an important tool that is critical to improving selective breeding of this species.