Effect of seasonal water temperature variation on the blood serums thyroid hormone levels of juvenile chub fishes (Squalius cappadocicus)

In this study, the seasonal change (varying with water temperature) of thyroid hormones [Total triiodothyronine (TT3) and Total thyroxine (TT4)] in the blood serums of juvenile chub fish (Squalius cappadocicus) has been investigated. The research has been conducted on the chub fish caught in Melendiz Stream (Aksaray) at different times (2010–April, June, July, and November; 2011–February and March). As a result of the hormonal analyses on blood serums, TT3 and TT4 levels have shown meaningful changes (p < 0.05) inversely proportional to the water temperature. It made us think that this change is due to adaptation decreased/increased metabolic (energy) activity provided by the fishes against temperature stress.