In the present study, 60 male C. trutta within the age group of 2 year olds (the first year of puberty) and 3 year olds were collected in the Gheshlagh River, Sanandaj, during the breeding season (June and July, 2015) in order to examine total length, standard length, total weight, sperm quality (volume, motility duration, density, spermatocrit, seminal plasma pH and osmolity) and sex steroids (testosterone and DHP) levels. After calculation of GSI, testicular histology was also examined in order to compare. The total length, standard length, and total weight were significantly higher in the age group of 3 year than that in the age group of 2 year olds. No significant difference was found regarding milt volume, spermatocrit, seminal plasma pH and osmolity between the two age groups. However, motility duration and sperm density were significantly higher in the age group 2 year. In addition, GSI in the age group of 3 year olds was significantly higher than that observed in the age group 2 year olds. The sex steroids levels of testosterone and DHP were not significantly different between the two age groups. Histological studies showed that in both age groups testes are observable in different stages of germ cell development and testicular tissue structure of both age groups were the same at spermiation stage without dominance of certain groups of germ cells and