Vol. 41 No. 1, 2002

Effects of Exogenous Cortisol and Progesterone on Metallothionein Expression and Tolerance to Waterborne Cadmium in Tilapia (Oreochromis mossambicus)

Su-Mei Wu*, Yi-Ying Chou and Am-Ni Deng

Department of Aquatic Biosciences, National Chiayi University, Chiayi, Taiwan 600

Su-Mei Wu, Yi-Ying Chou and Am-Ni Deng (2002) The object of the present study was to test the hypothesis that glucocorticoids can induce the expression of metallothionein (MT) which consequently enhances the tolerance to metal toxicity in tilapia (Oreochromis mossambicus). Adult tilapia (4-5 cm in total length and 5.0-6.0 g in body weight) and larval tilapia (0.5-0.7 cm in total length and 0.012-0.017 g in body weight) were reared with artificial feed containing 0 (control), 50 (low dose), 125 (medium dose), or 250 mg/kg (high dose) of cortisol or progesterone for 10 d. Liver and wholebody contents of MT and mortality in tilapia upon Cd²⁺ exposure were examined after the steroid-rearing experiments. Both cortisol and progesterone significantly increased survival rates in adult fish after Cd²⁺ challenge. Treatment with middle and high doses of progesterone significantly stimulated the expression of MT in adult fish, but stimulation by cortisol showed no significant effect on MT expression. More MT was expressed after Cd²⁺ challenge in both cortisol- and progesterone-treated groups. However, exogenous steroids caused no significant effect on MT contents or survival upon Cd²⁺ challenge in tilapia larvae. This suggests that cortisol and progesterone are involved in metal-detoxification mechanisms in adult tilapia via regulating the expression of MT, but the occurrence of this pathway in developing fish is unclear.

Key words: Corticosteroid, Metallothionein, Cadmium, Tolerance, Tilapia.

*Correspondence: Tel: 886-5-2717850. Fax: 886-5-2717847. E-mail: sumei@mail.ncyu.edu.tw