Effects of Dietary Astaxanthin on Growth, Coloration, Immunity, and Antioxidant Capacity in Macrobrachium Rosenbergii

This study investigated the effects of astaxanthin (Ax) on the growth, body color, and immunity of Macrobrachium rosenbergii. 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 M. rosenbergii. 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; p < 0.05) and shortened the molting cycle (p < 0.05). Addition of Ax increased the redness (a ^{⁣ ∗} value) and yellowness (b ^{⁣ ∗} value) of live and cooked M. rosenbergii (p < 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 M. rosenbergii (p < 0.05) and significantly decreased the activity of malondialdehyde (MDA; p < 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 (p < 0.05). Additionally, there were significant differences in the expression levels of molting-related genes (ecdysteroid receptor (EcR) and retinoid X receptor (RXR)), 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 M. rosenbergii but also enhanced its immune and antioxidant capabilities. This study provides a reference for the application of Ax in crustacean feed.