Dietary Astaxanthin Improves Growth, Modulates Skin Antioxidants and Transcriptomics in Koi Carp (Cyprinus carpio) Under Acute Cold Stress

Abstract

Cold stress disrupts redox homeostasis and skin structural integrity in ornamental koi carp (Cyprinus carpio). To address the unclear long-term effects of astaxanthin (AX), this study examined 90-day dietary supplementation on growth and skin-derived antioxidant mechanisms during cold shock and recovery. Koi carp were administered with one of the 5 diets containing the following 0 mg/kg (AX0), 25 mg/kg (AX25), 50 mg/kg (AX50), 75 mg/kg (AX75) and 100 mg/kg (AX100) of astaxanthin for 90 days then growth performance are measured; antioxidant of the fish skin was assessed thereafter they were exposed to an acute transfer to a temperature of 13 °C; MDA, GSH, SOD, CAT, protein carbonyls, and GPX were measured in skin samples collected after 90 days of dietary AX, following cold-stress exposure, and after the recovery period. Transcriptomic analysis and protein–protein association network analysis were performed for the AX0 and AX75 groups following cold-stress exposure and after the recovery period. AX75 treatment showed the highest growth performance. Under cold-stress conditions, the AX0 group exhibited higher MDA levels and lower SOD activity, whereas the AX75 group showed lower MDA levels and higher SOD activity. During the recovery period, AX75 showed increased CAT activity and GSH levels, along with low levels of MDA and protein carbonyls in comparison to the AX0 group. Transcriptomic analysis revealed diet-associated differential expression of candidate genes related to pentose phosphate and redox metabolism. Overall, the results of this study showed that 75 mg/kg astaxanthin enhanced growth and produced the strongest antioxidant response against cold stress and assisted in recovery.