Zoological Studies

Vol. 39 No. 1, 2000

Sex Differences in the Responses of Serum Calcium Concentrations to Temperature and Estrogen in Tilapia, Oreochromis mossambicus

Ching-Lin Tsai* and Li-Hsueh Wang

Department of Marine Resources, National Sun Yat-sen University, Kaohsiung, Taiwan 804

Ching-Lin Tsai and Li-Hsueh Wang (2000) Sex differences in the responses of serum calcium concentrations to temperature and estrogen in tilapia, Oreochromis mossambicus, were investigated. Prespawning males and females were kept at 26, 29, and 32C aquatic temperatures for 21 d. The serum calcium levels increased by elevated temperature in females but were not altered in males. Females showed higher serum calcium levels than males at the 26, 29, and 32C exposure groups, respectively. On the other hand, males and females were gonadectomized and treated with different dosages of 17β-estradiol for 21 d. Serum calcium levels significantly decreased after gonadectomy in females but were not altered in males. There was no difference in serum calcium levels between gonadectomized males and females. Treatment with 17β-estradiol at 50 or 100 mg/kg diet significantly increased serum calcium levels dose-dependently in both gonadectomized males and females. The hypercalcemic effect of 17β-estradiol was greater in castrated males. These results suggest that the estrogen induced calcium regulatory system is temperature dependent in females and not in males. On the other hand, estrogen induced elevation of blood calcium level is more pronounced in males than in females.

Key words: Estradiol, Serum calcium, Sex difference, Temperature, Tilapia.

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