The present study aimed to investigate growth performance of Nile tilapia fry (2.09 initial weight) and survival as affected with stocking density (50.?5and 100 fry 1 in!) when reared in concrete tanks during winter season . Twelve concrete tanks (10m3 volume each) were used In this study representing the three stoking density within each uncovered or 75% of the surface was covered with polyethylene sheets. Each treatment was represented by two replicates. The study was started at the first of October 2005 and lasted to the end of March2006 (6 months duration). Results obtained are summarized in the following: 1) Both stocking density and tank cover released significant effects on final body weight and survival in favor of lower stocking density and tank covering with plastic sheets. ‘ 2) Treatments applied released significant effects on water quality parameters tested. Regardless of staking rate. treatment groups of the covered tanks improved all parameters of water quality 3) Values of proximate analysis of whole fish bodies for moisture. protein and ash contents were decreased insignificantly by the treatment applied, however fat contents in the whole body were increased but also insignificantly. Keywords: Over-wintering. Tanks, Nile tilapia, Growth. Survival, Water temperature, Economic efficiency.