Aim of this study is to determinate oxygen consumption rate of Black Sea trout, (Salmo trutta labrax Pallas, 1811) in the sea water (18‰ salinity) in tanks at farm condition. Two different fish size were used as small size and big size which average weights 54.1 ±3.06 (n=300) and 507.0 ±17.71 (n=32) g, average total lengths 17.7 ±0.36 and 35.5 ±0.44 cm respectively. Water temperature averaged 10.0 ±0.01°C during the experiment. The amount of dissolved oxygen was measured during 3 days inlet and outlet of each tank. Oxygen consumption rate was found to be in the range of 95.2-140.0 mgO2kg/h according to fish size. It was observed that O2 con-sumption increased in the daylight period.