Abstract. The objective of the present study was to investigate the importance of the antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GPX) in the defense against lipid and protein oxidation in spawn from female brown trout, Salmo trutta m. trutta L. affected by ulcerative dermal necrosis (UDN). UDN induced increased lipid and protein oxidation levels. The current results show that UDN infection led to oxidative stress with the inhibition of antioxidant defense mechanisms. The inhibition of glutathione defense system activity might be responsible for this failure in cellular antioxidant defenses. UDN induces irreversible changes in pro-and antioxidative function which effected decreased spawn survival as well as reductions in spawning efficiency.

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In the present work we evaluated the effect of ulcerative dermal necrosis (UDN) syndrome on resistance of erythrocytes to haemolytic agents and lipid peroxidation level in the blood from brown trout (Salmo trutta m. trutta L.). Results showed that lipid peroxidation increased in erythrocytes, as evidenced by high thiobarbituric acid reactive substance (TBARS) levels. Compared to control group, the resistance of erythrocytes to haemolytic agents was significantly lower in UDN-positive fish. Besides, UDN increased the percent of hemolysated erythrocytes subjected to the hydrochloric acid, urea and hydrogen peroxide. Results showed that UDN led to an oxidative stress in erythrocytes able to induce enhanced lipid peroxidation level, as suggested by TBARS level and decrease of erythrocytes resistance to haemolytic agents.