The present study investigated the effect of <i>Ligula intestinalis</i> L. infection on several components of the antioxidant system and on protein oxidation in the host fish, common bream <i>Abramis brama</i> L. In ligulosed bream, the hepatopancreatic antioxidant system response included a decrease in catalase (CAT) activity, an increase in glutathione S-transferase (GST) activity, and no change in superoxide dismutase (SOD) activity. Here, CAT is linked to infection.