Opposite effects of 17β-estradiol and combined growth hormone—Cortisol treatment on hypo-osmoregulatory performance in sea trout presmolts, Salmo trutta

Abstract

In March, sexually immature sea trout presmolts ( Salmo trutta trutta) were injected every second day with saline, 2 μg 17β-estradiol (E 2)/g, 2 μg ovine growth hormone (GH) + 6 μg cortisol (F)/g, or all three hormones (E 2-GH-F) simultaneously. A SW-challenge test was performed after six injections. At the time of SW-transfer, high total plasma calcium levels in E 2- and E 2-GH-F-treated fish indicated activated vitellogenesis in these groups. All control, GH-F, and E 2-GH-F-treated fish survived SW-transfer, whereas 43% of the E 2-treated fish died after transfer. On Day 2 after transfer, there were marked differences among groups in their osmoregulatory response. Changes in ion-osmotic parameters (plasma Na +, Cl −, Mg 2+, and total calcium and muscle water) indicated the following degree of osmotic stress: E 2 > control > E 2-GH-F > GH-F, which was inversely correlated with pretransfer gill Na + K + -ATPase activity: GH-F > E 2-GH-F > control > E 2. On Day 7 after transfer there were no major differences among the groups with regard to plasma ions and muscle water content. The detrimental influence of elevated plasma E 2 levels on hypo-osmoregulatory physiology may indicate an important role of E 2 during development.