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. A relatively new cultivar is the Australian barramundi (Lates calcarifer), a protandrous sequential hermaphrodite that takes several years to change from male to female. This delay prevents inter-generation breeding and hinders the establishment of sustainable genetic enhancement programs. In sequential hermaphrodites, sex change derives from the delicate balance between two steroids, 17β-estradiol (E2) and 11-ketotestosterone (11-KT). Here, we examined whether the generation time of fertile barramundi females could be shortened by injections of E2, which was administered in ethylene-vinyl-acetate (EVAc) implants at three doses of 0.5, 1, and 1.5 mg/kg BW; control fish received 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 2 months after the last injection. The proportions of females in the 0.5, 1, and 1.5 mg/kg treatment groups were 80%, 85%, and 75%, respectively, with no females found in the control group. Finally, treated females were tested for spawning induction, resulting in successful fertilization in both 2020 and 2021. Based on these results, we recommend using this protocol, specifically the 1 mg/kg dose, to reduce the generation time of fertile females by 2 years. This protocol can be utilized effectively in the commercial production of barramundi for selective breeding programs in Israel.