Effect of elevated temperature on estrogenic induction of vitellogenesis and zonagenesis in juvenile Atlantic salmon (Salmo salar)

Abstract

Fertility and embryo survival rates are often low in eggs from thermally challenged Tasmanian Atlantic salmon, partly due to a reduction in plasma 17߭estradiol (E2) levels. We used juvenile Atlantic salmon to assess whether hepatic tissue remains responsive to stimulation by E2 at the higher temperatures sometimes encountered by Tasmanian salmon during summer. E2 administration stimulated vitellogenin (Vtg) and estrogen receptor alpha transcription at 14àand 22ì although induction of Vtg occurred more rapidly at 22î Consequently, plasma Vtg levels increased and reached a plateau more quickly at 22î Zona pellucida (Zp) B and C transcription was significantly lower in E2-treated fish at 22àrelative to 14î This shows that the Vtg gene is E2-responsive at high temperature unlike Zp B and C genes that displayed traits of thermal inhibition. Therefore, estrogen replacement therapy in adult salmon may offset some, but not all thermal inhibition of reproductive function.