Induction of precocious females in the protandrous barramundi (Lates calcarifer) with long-acting estradiol implants

With the growing demand for fish protein, more aquatic species are currently being introduced into aquaculture. The Australian barramundi ( Lates calcarifer ) is a protandrous sequential hermaphrodite changing its sex from male to female. It takes several years for the barramundi to change from male to female which prevents inter-generation breeding and creates and obstacle for the establishment of a sustainable genetic enhancement program. In sequential hermaphrodites, sexual maturation as one sex or the other derives from the delicate balance between two steroids: 17β-estradiol (E2) and 11-ketotestosterone (11-KT), and as in other vertebrates, ovarian development is correlated to the rising levels of E2 as a response to FSH activity. In this work we aimed to shorten the generation time of the barramundi grown by Israeli aquaculture via injection of E2 ethylene-vinyl-acetate (EVAc) implants in three different doses, 0.5, 1, and 1.5 mg/kg BW and a control group with empty implants. An endocrine profile for E2 and 11KT and gonadal biopsies were examined throughout the study. Our results showed significant differences in E2 levels between the treated groups and the control, two months after the last given treatment. Furthermore, oocyte diameter increased accordingly in the treated fish exhibiting over 75% sex change. Finally, treated females were used for spawning induction resulting in successful fertilization both in 2020 and 2021. This protocol producing fertile females and shortening the generation time by two years and can be utilized in commercial production of barramundi for selective breeding programs in Israel.