TEMPORAL MODULATION OF OXIDATIVE STRESS AND ANTIOXIDANT CAPACITY IN RAINBOW TROUT (ONCORHYNCHUS MYKISS WALBAUM) FOLLOWING YERSINIA RUCKERI VACCINATION

This study investigated the temporal effects of Yersinia ruckeri vaccination on markers of oxidative stress and antioxidant capacity in the livers of rainbow trout (Oncorhynchus mykiss Walbaum). Oxidative stress was assessed using 2-thiobarbituric acid-reactive substances (TBARS), oxidatively modified protein (OMP) derivatives and total antioxidant capacity (TAC) at three time points: baseline and one and two months post-vaccination. TBARS levels exhibited a transient peak one month after vaccination, suggesting a short-term increase in lipid peroxidation associated with immune activation. In contrast, TAC increased progressively over the experimental period, reaching significantly higher levels in vaccinated fish after two months, which is indicative of enhanced systemic antioxidant defences. OMP derivatives exhibited moderate variability: aldehydic forms peaked in the control group at one month, while ketonic forms were highest at baseline. However, no significant vaccination effect was observed. Correlation analysis revealed a strong negative association between TBARS and TAC (r = −0.58), supporting the role of antioxidant capacity in mitigating oxidative damage. Effect size and variability analyses confirmed substantial time- and treatment-related changes, particularly with regard to TBARS reduction and TAC enhancement in vaccinated fish. Overall, the results demonstrate a biphasic oxidative response to vaccination characterised by an initial oxidative challenge followed by adaptive antioxidant upregulation, highlighting the importance of modulation of redox balance in immune protection and aquaculture health management.