In commercial production conditions, rainbow trout fry that average live weight is 1.3 ± 0.2 g were placed in rectangular concrete ponds of 44 cubic meters with 15, 20, 40 and 60 fish/m3 stocking density, respectively, and fed for 270 days at an average water temperature of 8.3°C between June and February during which the growth and feed conversion ratios of fish were determined. At the end of the study, the best results were achieved with the stocking density of 1 5 fish/m3, and this was followed by the stocking density of 20 fish/m3. Stocking densities of 40 and 60 fish/m3 have shown lowest results and there has been no statistically significant difference between these two groups. When evaluating the feed conversion rate and specific growth rate of fish, no significant difference was observed between the experimental groups. The study concluded that low water temperatures has no positive effect on stocking density in commercial rainbow trout production.