[Objective] The study aimed to discuss the effects of ferrous fumarate on growth performance, blood biochemical parameters and content of trace element of Oncorhynchus mykiss. [Method] Juvenile rainbow trout with an initial weight of (89.2±0.2) g were fed with the basal fodder supplemented with different levels of ferrous fumarate (0, 20, 40, 80, 160 and 480 mg/kg iron) for 60 d, and the six groups were named D0, D20, D40, D80, D160 and D480, wherein D0 was as the control group, actually containing 62.60, 79.50, 99.60, 139.30, 215.20 and 538.40 mg/kg iron respectively. [Result] The growth performance of juvenile rainbow trout was not affected by different dietary iron levels obviously (P>0.05). With the increase of dietary iron level, hemoglobin (Hb) content and number of red blood cells(RBC) rose firstly and then leveled off. No significance was found in hematocrit (Hct) among the six groups (P>0.05). Iron content in the whole body, vertebrae and muscle increased significantly with the improvement of dietary iron level(P0.05), while zinc content in the vertebrae and muscle in control group was significantly higher than that of other groups (P0.05), and copper concentration in the muscle in control group was significantly lower than that of other groups (P0.05). Catalase (CAT) activity of serum enhanced significantly (P<0.05) from D0 to D40 and then decreased obviously (P<0.05). [Conclusion] Based on hemoglobin and iron content in the liver, the broken-line model analysis showed that the dietary iron level provided by ferrous fumarate for juvenile rainbow trout was estimated to be 99.8 and 100.4 mg/kg respectively in the experiment.
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