Optimal Dietary Dunaliella salina Supplementation Enhances Growth, Antioxidant Capacity, Immune Response, Stress Tolerance, and Carotenoid‐Based Pigmentation in Juvenile Red Swamp Crayfish ( Procambarus clarkii )

To meet the growing market demand for high‐quality red swamp crayfish ( Procambarus clarkii ), nutritional strategies are needed to improve both health and visual traits. The microalga Dunaliella salina , renowned for its rich natural β‐carotene content, presents a promising solution. This study investigated the effects of dietary supplementation with D. salina powder at five graded levels (0%, 0.34%, 0.67%, 1.34%, and 2.00%) on juvenile crayfish over a 60‐day feeding trial. Results demonstrated that weight gain rate (WGR) and specific growth rate (SGR) were highest in the 2.00% supplementation group. Notably, a low inclusion level of 0.34% significantly promoted ovarian development, as evidenced by the highest gonadosomatic index (GSI) and digestive enzyme activities. Antioxidant capacity (AOC, total superoxide dismutase [T‐SOD], total AOC [T‐AOC]) and nonspecific immunity (alkaline phosphatase [AKP]) were maximally enhanced at 0.67% inclusion. Most importantly, dietary D. salina was efficiently converted to astaxanthin and deposited in tissues, with carapaces and ovaries coloration parameters showing a strong, dose‐dependent correlation with carotenoid accumulation. Regression analysis identified an optimal inclusion range of 1.23%–1.53% for maximizing carotenoid deposition, immune function, and AOC. Furthermore, the 2.00% supplementation group exhibited the highest tolerance to air exposure stress. Our findings provide definitive, data‐driven insights for the precise application of D. salina in functional crayfish feeds, facilitating the industry’s transition from quantity‐focused production to quality‐ and value‐driven aquaculture.