皮質素醇在吳郭魚胚胎及仔魚初期之離子調節功用

Abstract

The effects of cortisol on the ionic-regulation in embryos and larvae of the tilapia (Oreochromis mossambicus) was studied. This report includes two parts, one is the calcitropic effect of cortisol in freshwater-adapted tilapia larvae, the other is the effect of cortisol on osmoregulation in freshwater-adapted tilapia larvae during seawater challenge. In the first part, embryos and larvae of the tilapia were incubated in different concentrations of cortisol (i.e. 1, 5, 10, 15 mg/l) for 3-6 days and then sampled for determination of cortisol content, calcium content, calcium influx and body weight. The treatment of exogenous cortisol increased cortisol content of tilapia larvae significantly, but had no obvious effect on calcium content and calcium influx. In order to induce the calcitropic effect of cortisol, the concentration of exogenous cortisol and incubation time were enhanced. The embryos and larvae of the tilapia were incubated in high doses of cortisol (i.e. 10 and 100 mg/l) for 9 days and then transferred from normal calcium environment (0.15 mM) to low calcium environment (0.01 mM). Even in such experimental conditions, the calcitropic effect of cortisol was still not significant. In the second part, the embryos and larvae of the tilapia were incubated in 10 mg/l of cortisol for 3-4 days and then transferred from fresh water to sea water. Treatment with cortisol significantly reduced the cumulative mortality and sodium content of tilapia larvae during seawater challenge, suggesting that cortisol participate in hypo-osmoregulation of tilapia larvae during seawater adaptation.