Using response surfaces to explore the interactive effect of dietary astaxanthin and beta-carotene on growth and antioxidant capability of juvenile Chinese mitten crab, Eriocheir sinensis

Although the biological properties of astaxanthin (Axn) and beta-carotene (beta-car) on aquatic animals have been widely investigated, such properties are still typically studied by incorporating different levels of a single carotenoid, or in combination using a traditional factorial design. In the present research, nutritional geometry was applied to more efficiently and powerfully investigate the interactive effects of Axn:beta-car ratios and total carotenoid level on the growth, antioxidant status, colour parameters, and carotenoid composition of juvenile Eriocheir sinensis. Experimental diets were formulated to contain four levels of total carotenoid content (25, 50, 75 and 100 mg/kg) and at each level there were three different Axn:beta-car ratios (4:1, 1:1 and 1:4). The results showed that: (1) Hepatosomatic index (HSI) significantly increased with Axn supplementation, and the highest value was observed in 80 mg/kg Axn treatment. (2) Indicators of antioxidant capacity (T-AOC, MDA) significantly improved in the hepatopancreas and hemolymph with the increase of total carotenoid supplementation. (3) Other indicators of immunity (AKP, ACP) and physiological status (GPT, GOT) were optimal between 50 and 75 mg/kg carotenoid inclusion and at a 1:1 of Axn: beta-car ratio in either or both tissues. (4) For colour enhancement, the redness of carapace and hepatopancreas increased significantly with the increase of both Axn:beta-car ratio and total carotenoid level. Combined, the diets comprising 1:1 ratio of Axn:beta-car and 75 mg/kg of total carotenoid level could be the optimal and most cost-effective alternative to diets containing Axn alone, to maximize the quality and resilience of juvenile E. sinensis in culture.