Dietary DL-α-Tocopheryl Acetate Enhances Thermal Tolerance and Modulates Oxidative Stress Responses in Juvenile Rainbow Trout (Oncorhynchus mykiss)

Rising water temperatures necessitate nutritional strategies to enhance resilience in rainbow trout (Oncorhynchus mykiss). This study evaluated the effects of dietary vitamin E on thermal tolerance and physiological, antioxidant, and hepatic molecular responses to gradual warming. Juvenile trout (22.44 ± 0.03 g; mean ± SD) were fed CTRL, LDvitE, and HDvitE diets with analyzed α-tocopherol levels of 206.5, 265.6, and 608.1 mg/kg, respectively, for 60 days. Thermal tolerance was assessed using critical thermal maximum (CTMax), and thermal stress responses were evaluated during gradual warming from 17 to 24 °C (1 °C/day). At the end of the feeding period (Final), compared with CTRL, LDvitE and HDvitE showed lower hepatic TBARS levels, higher CAT activity, and higher expression of hepcidin and α-ttp. HDvitE also had lower serum cortisol and AST and a significantly higher CTMax than CTRL. Following thermal stress (Post-stress), serum cortisol and AST remained lower in HDvitE than in CTRL, with the lowest serum glucose level in HDvitE. Hepatic hsp90 and defb3 expression levels were higher in HDvitE than in CTRL. Overall, HDvitE improved thermal tolerance and was associated with favorable physiological and molecular responses before and after thermal stress, supporting its potential to enhance thermal resilience in rainbow trout.