The age determination method and its accuracy are the most important subjects for the evaluation of age-length-weight relations in fisheries biology, since estimates of survival, growth and mortality rates, analysis of year-classes, and recruitment all depend on age structure. Thus, the aim of this study was to determine the most reliable bony structure for ageing Perca fluviatilis inhabiting Derbent Dam Lake. Scales, vertebrae, otoliths and opercles removed from each fish were examined by 2 readers 3 times, without referring to any information except for the date of capture and gonad state. The precision of the readers was estimated and ageing error was determined by analysis of variance. Due to their having the highest precision and the lowest ageing error, vertebrae were determined to be a reliable bony structure for ageing this species.