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

Fertility and embryo survival rates are often low in eggs from thermally challenged Tasmanian Atlantic salmon, partly due to a reduction in plasma 17 beta-estradiol (E-2) levels. We used juvenile Atlantic salmon to assess whether hepatic tissue remains responsive to stimulation by E-2 at the higher temperatures sometimes encountered by Tasmanian salmon during summer. E-2 administration stimulated vitellogenin (Vtg) and estrogen receptor alpha transcription at 14 degrees C and 22 degrees C, although induction of Vtg occurred more rapidly at 22 degrees C. Consequently, plasma Vtg levels increased and reached a plateau more quickly at 22 degrees C. Zona pellucida (Zp) B and C transcription was significantly lower in E-2-treated fish at 22 degrees C relative to 14 degrees C. This shows that the Vtg gene is E-2-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.