A Preliminary Study on the Effects of Hyperosmotic Stress on Plasma Levels of Thyroid Hormones in Male Catfish, Clarias gariepinus

Abstract

Male air-breathing catfish, Clarias gariepinus were exposed to hyperosmolar mannitol solution (250 mM) to determine its effect on the plasma levels of thyroxine (T₄) and triiodothyronine (T₃) during the winter, spring, summer and autumn seasons. During the winter season, hyperosmolar mannitol solution significantly increased the plasma levels of T₄ throughout the duration of exposure, whereas the plasma T₃ levels significantly increased only at 12-48 h. During the spring season, significant decreases in the plasma levels of T₄ were observed only at 12 and 48 h, and significant increases in the plasma levels of T₃ were observed only at 6-24 h. During the summer season, the plasma levels of T₄ significantly increased at 6 h and decreased at 24-48 h, while the plasma levels of T₃ significantly increased only at 6 and 24 h. During the autumn season, the plasma levels of T₄ significantly increased at 6, 12 and 48 h and the plasma levels of T3 significantly decreased at 6, 24 and 48 h. These results indicate the season-dependent and differential effects of the hyperosmolar mannitol solution on the plasma levels of thyroid hormones in Clarias gariepinus.