Age determination and annulus formation of the crucian carp (Carassius gibelio) obtained from Egirdir Lake between March 2001 and January 2003 and Bafra Fish Lake between January 2000 and September 2002 were evaluated by examination of scales, otoliths, vertebrae, opercular bones, and subopercular bones. The precision of age estimation was derived by percentage of reader agreement and coefficient of variation (CV). The highest agreement (70.3%) and lowest CV (7.0%) were with otoliths for Egirdir Lake specimens; in Bafra Fish Lake specimens, the highest agreement and lowest CV were with vertebrae 62.9% and 8.1%, respectively. We found that the most reliable bony structure for age determination varied in different populations of this species. Marginal increment analysis showed that annulus formation occured during October-April.