Maintenance of Atlantic salmon (Salmo salar) at elevated temperature inhibits cytochrome P450 aromatase activity in isolated ovarian follicles

Atlantic salmon (Salmo salar) broodstock were transferred from natural (12-16°C) to controlled temperatures of 14, 18 or 22°C for 3 months during vitellogenesis. Fertility and survival were significantly reduced in eggs from broodstock held at 22°C relative to 14 or 18°C. Endocrine mechanisms were disrupted after only one month at 22°C, as evidenced by decreased plasma vitellogenin (Vtg) and increased plasma testosterone (T) levels and, at later stages, decreased levels of plasma 17β-estradiol (E2). In vitro incubations of isolated ovarian follicles were carried out at monthly intervals, with follicles exposed to human chorionic gonadotropin, N-2-0-dibutyryladenosine 3,5-cyclic monophosphate, and the gonadal steroid precursors 17-hydroxyprogesterone, androstenedione, and T. After one month of exposure to controlled temperature, T synthesis was generally enhanced in response to all treatments at all temperatures, but E 2 synthesis was inhibited at 22°C, suggesting temperature impairment of cytochrome P450 aromatase (P450arom) synthesis or activity. The effect became less marked as follicles matured suggesting that temperature sensitivity is stage dependent. The results of this study suggest that the inhibitory effects of elevated temperature on E2 and Vtg synthesis, and subsequent egg development found in the present and earlier studies, arise at least partly, from temperature modulation of P450 arom. © 2003 Elsevier Inc. All rights reserved.