This study investigated seasonal variations of antioxidant defense enzyme activities: total, manganese, copper zinc containing superoxide dismutase (Tot SOD, Mn SOD, CuZn SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and biotransformation phase II enzyme glutathione-S-transferase (GST) activity in the liver and white muscle of red mullet (Mullus barbatus). The investigations were performed in winter and spring at two localities: Near Bar (NB) and Estuary of the River Bojana (EB) in the Southern Adriatic Sea. At both sites, Mn SOD, GSH-Px, GR and GST activities decreased in the liver in spring. In the white muscle, activities of Mn SOD, GSH-Px, GR and GST in NB decreased in spring. GR decreased in spring in EB, while CAT activity was higher in spring at both sites. The results of Principal Component Analysis (PCA) based on correlations indicated a clear separation of various sampling periods for both investigated tissues and a marked difference between two seasons. Our study is the first report on antioxidant defense enzyme activities in the red mullet in the Southern Adriatic Sea. It indicates that seasonal variations of antioxidant defense enzyme activities should be used in further biomonitoring studies in fish species.

The activities of total superoxide dismutase (Tot-SOD), manganese-containing superoxide dismutase (Mn-SOD), copper zinc containing superoxide dismutase (Cu/Zn-SOD) and catalase (CAT) protein concentration, as well as protein and SOD electrophoretic profiles in the liver and muscle of barbel (Barbus barbus) and its intestinal parasite Pomphoryinchus laevis from the river Danube, within the suburban area of Belgrade, Serbia (the stretch between Visnjica and Grocka) in spring and summer were investigated. Specific activities of Tot-SOD, Mn-SOD, Cu/Zn-SOD were higher in spring, while specific CAT activity was higher in summer in all investigated samples. Temperature influence on the antioxidant defense enzymes in barbel tissue and in its intestinal parasite Pomphoryinchus laevis, as well as seasonal patterns, are evident. Our work represents the first study of SOD and CAT activities in the barbel and its intestinal parasites and shows that barbel and acanthocephalans are very useful for biomonitoring studies in aquatic ecosystems.

We determined the contents of total glutathione (tGSH), reduced glutathione (GSH), and oxidized glutathione (GSSG) and values of the glutathione redox index (GSH RI) in hepatopancreas, gills, and muscle of three freshwater crayfish species: noble crayfish (Astacus astacus) from the Southern Morava River, stone crayfish (Austropotamobius torrentium) from the Krajkovacka River, and spinycheek crayfish (Orconectes limosus) from the Danube River. The obtained data show strong tissue and species specifity of investigated parameters: tGSH, GSH, GSSG, and GSH RI in the hepatopancreas, gills, and muscle of the indicated crayfish species. Our work represents the first study of its kind and showed that the investigated parameters can be considered suitable biomarkers of the cellular glutathione redox status in of freshwater crayfish species.