The effects of four stocking densities of 20, 40, 60, 80 mussels/m² on growth of Unio tigridis were investigated. The growth of the freshwater mussel U. tigridis in cages was studied for a year from March 2003 to April 2004 in Lake Gölbaşļ. Juvenile mussels with the initial weight of 0.64 ± 0.08 g were stocked in metal cages placed on the lake bottom. Growth in live weight, shell length, width and height was measured monthly for the four different stock groups. Chlorophyll a, magnesium (Mg), nitrite (NO₂), nitrate (NO₃), amount of organic matters, ammonia (NH₃), phosphate (PO₄), silica (Si) and calcium (Ca) were also analyzed monthly. All water quality parameters were within proper limits for mussel culture. At the end of the study, the greatest live weight (5.55 ± 0.03 g) was obtained from 40 mussels/m², with 3.5 2 ± 0.02 cm and 1.47 ± 0.03 cm as length and width values, respectively. The greatest height was determined in a stocking rate of 60 mussels/m², with 1.99 ± 0.03 cm. Therefore, juveniles should be stocked in early spring for U. tigridis at a level of 40–60 individuals/m².