Seasonal changes of the thyroid gland structure
and hormones secretion was examined in yellowfin seabream (Acanthopagrus
latus) in the northwest of Persian Gulf (Musa creek). Thyroid gland composed
of follicles scattered around the ventral aorta, near the gills. Follicular
cells varied according to secretion of the gland during warm and cold seasons. Thyroid hormones (Triidothyronine [T3]
and Thyroxine [T4]) were detected in the fish
serum in levels ranged from 4.09-1.30 ng/mL for T3 and from 1.10-0.21 ng/mL for
(T4) in the warm and cold seasons, respectively. The results showed that the
height of thyroid epithelium and plasma concentration of thyroid hormones (thyroid
activity) in A. latus increased significantly during spring and summer.
The peak of these factors occurred in midsummer (August). Then, the thyroid
activity decreased significantly during autumn and early winter from
October to December according to decrease of temperature. T3 and T4 increased
significantly from January to April.