Tench (Tinca tinca) is an abundant and commercially important cyprinid in shallow vegetated lakes throughout much of Europe and Asia. The current study provides biological baseline data for the population of tench in Hirfanli Dam Lake, and determines if reproduction characteris-tics of the Hirfanli population differs from those in surrounding regions. The overall ratio of males to females was 0.92:1.00, with an age distribution of I-VI age groups, and sexual matur-ity attained at age III (for males) and IV (for females). Spawning occurred from the end of May to the mid of July, with mean absolute fecundity of 113305 ± 97826 eggs (±S.D) and relative fecundity of 347 ± 228 eggs mm-1 of fork length and 184 ± 52 eggs g-1 of total body weight. These fecundity values for tench in Hirfanli Dam Lake differ markedly from those in other re-gions of Turkey, and must be taken into account when considering lake’s future as a resource for fishing and irrigation.