Role of the thyroid gland in ovarian maturation of the goldfish, Carassius auratus L.

Abstract

Thyroxine (T₄) stimulated ovarian development in immature intact goldfish after both 8 and 17 weeks of treatment. T₄ alone had no influence on ovarian development in hypophysectomized regressed adult individuals, but did augment the ovarian response to salmon gonadotropin (SG-G100) after pituitary ablation. Pituitary gonadotropin cell and nuclear diameters in maturing fish were decreased after T₄ treatment, while immersion of immature fish in the goiterogen, 6n-propy1-2-thiourucil, resulted in a slight increase in these values. Hepatosomatic index values were higher in T₄-treated hypophysectomized fish than in controls.The findings indicate that thyroid hormones act synergistically with gonadotropin to influence ovarian development in goldfish and suggest that these effects are mediated, directly or indirectly, by a T₄-induced increase in ovarian sensitivity to gonadotropic stimulation. Thyroid hormones appear to inhibit gonadotropin production in this species, although the physiological significance of this is uncertain.