In this study, the effects of four different stocking densities (20, 40, 60, 80 individuals/m(2)) were investigated on growth performance of the Unio terminalis delicates in a natural lake (Lake Golbasi, Kinkhan, Hatay, Turkey). Growth in live weight, shell length, width and height were measured monthly for the four different stock groups during 6 months. The highest growth rate was obtained from 40 ind./m(2)group, while the best condition factor was acquired from the lowest density group (20 ind./m(2)). The specific growth rate for length and weight were highest in June and July in all groups. On the other hand, plankton biodiversity, chlorophyll a, Mg, NO2, NO3, amount of organic matters, NH3, PO4, Si, Ca and chemical oxygen demand (COD) were determined as biological and chemical characteristics. At the end of the study, the greatest live weight (5.06+/-0.34 g) was obtained from 40 ind./m(2), with 3.34+/-0.05 cm, 1.36+/-0.03 cm and 1.91+/-0.04 cm as length, width and height values, respectively. Therefore, it could be advised that juveniles should be stocked in early spring for U. terminalis delicates at a level of 40 ind./m(2). This results suggest that stocking density is the key factor in mussels culture and important for captive breeding in mussels production.