Abstract: This study was carried out in order to determine possible seasonal effects on blood parameters of Capoeta trutta (Heckel, 1843), from Karakaya Dam Lake (Malatya, Turkey). Age-weight-length values of fish were determined seasonally during a year and the effect of these independent variables on blood parameters were investigated. Comparison of blood parameters was performed according to sex differences. Analysis revealed that the values of blood parameters increase in spring-summer period and decrease in autumn-winter period irrespective of age-weight-length variables. A significant (p<0.05) difference was found between female and male in reproduction period (spring-summer).