The metabolic level and growth rate of juvenile rainbow trout(Oncorhynchus mykiss) under four dissolved oxygen concentration(7.05 mg/L,8.82 mg/L of 100% saturation,11.84 mg/L and 15.80 mg/L,respectively)were investigated.The fish(mean initial body lenth 13.0-18.5 cm) was reared in closed recirculated water for 30 days.The results showed the rates of oxygen consumption and ammonia excretion reduced obviously in fish experiening hypoxia condition(7.05 mg/L).At hyperoxic conditions(11.84 and 15.80 mg/L),the rates of oxygen consumption increased significantly,and the rates of ammonia excretion were much higher at hyperoxic(15.80 mg/L) conditions compared to 8.82 mg/L normoxic saturations.In addition,there were actual changes in growth indexes that the growth gain rate,special growth rate and food conversion efficiency showed a clear enhancing tendency,with the increase of dissolved oxygen.