Suitable natural astaxanthin supplementation with Haematococcus pluvialis improves the physiological function and stress response to air exposure of juvenile red swamp crayfish (Procambarus clarkii)

High mortality during transportation has restricted industrial development of red swamp crayfish (Procambarus clarkii), especially juveniles, in China. Supplementation with Haematococcus pluvialis has been proved to promote crustacean survival and growth. Therefore, this study investigated the effects of dietary natural astaxanthin derived from H. pluvialis on the growth performance, pigmentation, digestion, antioxidant capacity, immunity, and response to air exposure stress of juvenile red swamp crayfish. Five isonitrogenous and isolipidic diets were formulated containing a graded H. pluvialis powder inclusion (0, 0.15, 0.30, 0.45 and 0.60%) level. The results indicated that dietary astaxanthin significantly improved the survival rate and weight gain rate of juvenile crayfish (P < 0.05). As dietary astaxanthin levels increased, a* values in the carapace, muscle, and ovaries improved and the carotenoid content significantly increased (P < 0.05). Lipase (LPS), and cellulase (CL) activities in the hepatopancreas and intestines, and α-amylase, and pepsin (PEP) activities in the hepatopancreas, significantly increased and then decreased with increasing dietary astaxanthin levels (P < 0.05). Dietary astaxanthin significantly decreased the malondialdehyde (MDA) content in the hemolymph (P < 0.05). Total superoxide dismutase (T-SOD), total antioxidant capacity and acid phosphatase (ACP) activities in the hepatopancreas and hemolymph, as well as alkaline phosphatase in the hepatopancreas, followed a similar pattern as the digestive enzymes (P < 0.05). Furthermore, dietary astaxanthin significantly improved succinate dehydrogenase (SDH) activity in the hepatopancreas and muscle after a 24-h air exposure stress test, while decreasing the MDA and lactic acid content (LD) in muscle (P < 0.05). Based on the quadratic regression analysis of LPS, PEP, CL, T-SOD, ACP and SDH in hepatopancreas, and MDA and LD in muscle, the optimal dietary natural astaxanthin content for juvenile red swamp crayfish ranges from 63.55 to 84.40 mg kg^-1.