Biomarkers of oxidative stress, biochemical changes, and the activity of lysosomal enzymes in the livers of rainbow trout (Oncorhynchus mykiss Walbaum) vaccinated against yersiniosis before a Yersinia ruckeri challenge

Introduction: This study aimed to evaluate biomarkers of oxidative stress (2-thiobarbituric acid reactive substances, aldehyde
and ketone derivatives of oxidatively modified proteins and total antioxidant capacity), the activity of antioxidant enzymes
(superoxide dismutase, catalase, glutathione reductase and glutathione peroxidase), that of lysosomal enzymes (alanyl aminopeptidase,
leucyl aminopeptidase, β-N-acetylglucosaminidase and acid phosphatase) and changes in biochemical parameters (alanine
aminotransferase, aspartate aminotransferase, de Ritis ratio, lactate dehydrogenase activity, lactate and pyruvate levels and their
ratio) in the liver tissue of fish that were vaccinated against enteric redmouth disease and challenged with its causative agent, the
bacterium Yersinia ruckeri. Material and Methods: The vaccine was administered orally to trout, some of which were challenged
with Y. ruckeri 61 days later. For comparison, unvaccinated and unchallenged trout and unvaccinated and challenged trout were
also evaluated. Results: In the unvaccinated fish, infection with Y. ruckeri disrupted the pro-oxidant/antioxidant balance, led to
a significant increase in lipid peroxidation and oxidative modification of proteins, decreased total antioxidant capacity and
significantly increased the activity of lysosomal enzymes. In vaccinated fish, the Y. ruckeri challenge increased the activity of
glutathione-related enzymes and decreased lipid peroxidation, anaerobic metabolism and the activity of lysosomal enzymes in fish
livers relative to the unvaccinated and challenged group. In contrast, these parameters increased after the Y. ruckeri challenge in
unvaccinated trout relative to those in the untreated group. Conclusion: Vaccination exerted a protective effect during the Y. ruckeri
challenge and had no adverse effect on fish livers.