In the recent years, identification and optimization of feed supplements used in the aquafeed industries as stimulastors of growth and immune system and color quality of fillet are considered as an important area in the nutrition of aquatic species. In this regard, astaxanthin (AX) is the most popular synthetic pigments. High cost, low bioavailability and variable purity have limited the use of AX in the industry [1]. Curcumin as a yellow pigment obtained from rhizomes of Curcuma longa is commonly used as a spice and food colouring. Curcumin and turmeric extracts have several pharmacological effects such as antitumour, anti-inflammatory, antioxidant and anti-infectious activities. In the present study, the potential of curcumin (CN) as a natural pigment in the diet of rainbow trout (45 ± 3.8 g) was compared to that of AX based on the some biological indices including growth performance (specific growth rate, % day-1), immunological indices (lysozyme and complement) and fillet quality. Five inclusion levels (mg kg-1) of CN (50, 100, 150, 200 and 250) and AX (30, 40 and 65) together with a basal diet (control) were used in the diet for 126 days. Results showed that immunological indices including lysozyme and complement levels of the serum of fish fed the diet containing 200 mg kg-1 increased (9.8 µg ml-1 and 11.2 unit ml-1, respectively) significantly (p≤0.05) compared to all inclusion levels of AX (mean: 6.9 µg ml-1 and 8.3 unit ml-1, respectively) and control diet (4.5 µg ml-1 and 5.1 unit ml-1, respectively). Using 200 mg kg-1 CN increased the final weight (197.8 ± 4.3 g) compared to all inclusion levels of AX (mean:168.1 ± 3.1 g) and control group (101.5 ± 5.1 g). Specific growth rate fish fed the diets containing 200 mg kg-1 CN (2.4 % day-1) increased significantly (p≤0.05) compared to all inclusion levels of AX (mean: 1.9 % day-1) and control diet (1.8 % day-1). Based on the L*a*b indices, the flesh quality of fillets in the fish fed the diets containing different levels of CN improved significantly (p≤0.05) compared to other treatments. Based on the results, using 200 mg kg-1 CN in the diet of rainbow trout was possible.

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