In this study, we analyzed the relative importance of food items of Chondrostoma regium Heckel, 1843. A total of 145 individuals were sampled between April 1993 and March 1994 in Suat Uǧurlu Dam Lake. Stomach content analysis was used to determine dietary composition. Relative measures of food item quantity were estimated by two different approaches: the Index of Relative Importance (IRI) and the Geometric Index of Importance (Gil). The results from these indices were compared and the most reliable way of estimating dietary composition was discussed. Navicula, Cymbella and Synedra were the most frequently consumed organisms. As C. regium mostly feeds on Bacillariophyta, it can be defined as planktivorous. Furthermore, ontogenic variations and the seasonal variation of food consumption were examined. The relation between the time of annulus formation on bony structures and feeding activity were also investigated. The deposition of hyaline rings were found to be synchronous with decrease in food diversity in autumn.