Abstract
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.