Knowing functional properties of native plants is an important area in fish nutrition. One of purposes of using medicinal plants in the diet of animals is to improve growth indices and flesh quality. Blackseed is a plant having antibacterial agents. Blackseed was used at five inclusion levels (1, 2, 3, 4 and 5 %) together with control diet in the isonitrogenous and isoenergetic diets of adult rainbow trout (56.5±3.9 g) for 63 days. Immunological indices (lysozyme and complement) and growth performance (specific growth rate, %/day) were measured. Results showed that immunological indices including lysozyme and complement levels of the serum of fish fed the diet containing 5% blackseed increased (11.8 µg/ml and 14.3 unit/ml, respectively) significantly (P≤0.05) compared to control diet (9.2 µg/ml and 9.8 unit/ml, respectively). Using 5% blackseed increased the final weight (158.8 ± 4.8 g) compared to control group (138.6 ± 5.3 g). Specific growth rate fish fed the diets containing 5% of blackseed (2.5%/day) increased significantly (P≤0.05) compared to control diet (1.8%/day). Based on the results, using blackseed at 5% in the diet of rainbow trout was possible

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