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.
Highlights
Osmotic conditions in an aquatic environment have a profound influence on various metabolic processes in the aquatic vertebrates
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
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
Summary
Osmotic conditions in an aquatic environment have a profound influence on various metabolic processes in the aquatic vertebrates. Changes in the osmolarity of the aquatic environment act as a stress and induce increase in the corticosteroid hormones that are commonly called stress hormones (Eddy F.B., 1981; Hegab S.A., 1984; Patino R.., 1988; Takei Y., 2006; Arjona F.J., 2008). Aquatic vertebrates have developed several adaptive strategies including osmotic regulation for their successful survival (Davenport J., 1985; Hanke W., 1985; Marshall W.S., 2006; Norris D.O., 2006). The immediate responses shown by the fish exposed to osmotic stress have been reported to affect their subsequent adaptations and survival (Eddy F.B, 1981; Wedemeyer G.A, 1981)
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