Abstract: The present study investigated the effects of dietary supplementation with astaxanthin from different sources on growth performance, flesh pigmentation, antioxidant capacity, and acute nitrite stress response in rainbow trout (Oncorhynchus mykiss). Four diets were designed as the control diet and three astaxanthin inclusion diets, including 3.0 g/kg Paracoccus carotinifaciens (PC), 2.4 g/kg Haematococcus pluvialis (HP), and 0.6 g/kg Carophyll Pink (CP), each providing 6 0 mg/kg astaxanthin. A total of 480 rainbow trout with an initial body weight of (6.17±0.08) g were randomly assigned to four groups with four replicates each, followed by a 30-day feeding trial. Results showed that there were no significant differences in growth performance between astaxanthin-supplemented groups and the control group (P>0.05). Muscle redness and yellowness values, as well as astaxanthin content, were significantly higher in all astaxanthin-supplemented groups than that in the control group (P<0.05), with the CP group showing the highest astaxanthin deposition in muscle. Antioxidant capacity was enhanced in all astaxanthin-treated groups, as evidenced by significantly elevated hepatic activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and catalase (CAT), along with reduced malondialdehyde (MDA) levels before and after acute nitrite exposure (P<0.05). Following nitrite challenge, plasma cortisol, glucose, and lactate levels were significantly lower in astaxanthin-fed groups compared to the control (P<0.05). Furthermore, astaxanthin supplementation significantly upregulated hepatic nrf2 and sod gene expression and downregulated bcl2 and caspase9 expression. In conclusion, dietary astaxanthin from three different sources improved the flesh color, pigmentation, antioxidant capacity, and anti-stress capacities in rainbow trout. However, PC and CP showed stronger effects in enhancing antioxidant capacity compared to HP, while HP exhibited a greater ability to alleviate cell apoptosis in rainbow trout.