INFLUENCE OF SEASON ON ANTIOXIDANT DEFENSE SYSTEMS OF Silurus glanis Linnaeus (Siluridae) AND Barbus capito capito Guldenstadt (Cyprinidae)

Seasonal fluctuations in antioxidant (superoxide disnutase, SOD; catalase, CAT; glutathione peroxidase, GPx; glutathione reductase, GR; glucose-6-phosphate dehydrogenase, G6PD) and biotransformation enzyme activities glutathione S-transferase, GST) and lipid peroxidation LPO) levels of livers and gills in European catfish (Silurus glanis) and Bulatmai barbel (Barbus capito capito) were determined. Superoxide dismutase, CAT, GPx, OR, G6PD and GST activities were higher in the liver compared to;ills for both species. The exception was being in B. capito capito where OR was higher in the gills compared to he than liver during autumn and winter. However, LPO levels were higher in the gills compared to the liver. At he end of present study, it was concluded that antioxidant defense system for both species were affected by many endogenous and exogenous factors. However, it is difficult to determine what is the most critical factor affecting OS in these species because of complex effects of these factors on the antioxidant defense system.