Effects of Dietary Astaxanthin on Growth, Coloration, Immunity, and Antioxidant Capacity in <i>Macrobrachium Rosenbergii</i>

This study investigated the effects of astaxanthin (Ax) on the growth, body color, and immunity of <i>Macrobrachium rosenbergii</i>. Four different concentrations of Ax (0, 50, 100, and 200 mg kg^-1) were supplemented in the basal diet to assess their impact on the growth, coloration, immunity, and antioxidant capacity in <i>M. rosenbergii</i>. After 10 and 20 weeks of feeding, compared to the control group, the addition of 100 mg kg⁻¹ of Ax significantly increased the weight gain rate (WGR) and specific growth rate (SGR; <i>p</i> < 0.05) and shortened the molting cycle (<i>p</i> < 0.05). Addition of Ax increased the redness (<i>a</i> ^{⁣ ^<i>∗</i>} value) and yellowness (<i>b</i> ^{⁣ ^<i>∗</i>} value) of live and cooked <i>M. rosenbergii</i> (<i>p</i> < 0.05), and the muscle Ax content increased as the amount of added Ax increased. The enzyme activity results showed that after 20 weeks of feeding, the inclusion of 200 mg kg^-1 of Ax significantly increased the activities of superoxide dismutase (SOD) and alkaline phosphatase (AKP) in <i>M. rosenbergii</i> (<i>p</i> < 0.05) and significantly decreased the activity of malondialdehyde (MDA; <i>p</i> < 0.05). Compared with control group, the addition of 100 mg kg^-1 of Ax significantly increased the expression levels of genes related to immunity and antioxidant activity (<i>p</i> < 0.05). Additionally, there were significant differences in the expression levels of molting-related genes (ecdysteroid receptor (<i>EcR</i>) and retinoid X receptor (<i>RXR</i>)), across the different Ax supplementation levels and molting stages. Considering all factors, the addition of 100 mg kg^-1 of Ax to the feed not only improved the growth performance and body color of <i>M. rosenbergii</i> but also enhanced its immune and antioxidant capabilities. This study provides a reference for the application of Ax in crustacean feed.