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Astaxanthin (AX) is one of the commonly used feed supplements to enhance the growth performance and provide antioxidant and immune functions of several aquatic animals. In the current study, juveniles of white-leg shrimp ( Litopenaeus vannamei ) with mean initial weight of 0.340 ± 0.041 g were fed with diets supplemented with 0 (control), 25, 50, 100, and 200 mg/kg feed for 8 weeks. At the end of the feeding trial, shrimps were exposed to  Vibrio harveyi , and their mortality rates were observed for additional 10 days. The growth indices in the AX-fed groups were significantly ( P  &lt; 0.05) higher than what were observed in shrimps in the control group. Dietary AX stimulated the final weight, weight gain, and specific growth rate and optimum growth levels were achieved at 100–200 mg AX/kg feed. Furthermore, the AX-enriched diets significantly enhanced feed intake more than the control diet, and the amount of AX had no effects on feed conversion ratios. In comparison to the control group, the AX-fed animals had significantly ( P  &lt; 0.05) higher villi length, villi width, and absorption area and their optimum values were observed at 100–200 mg AX/kg feed treatments. Moreover, the intestinal morphometry especially villi and its crypt, both internal and external tunica muscularis, and submucosal tissues did not show any inflammatory and/or degenerative changes in AX-fed shrimp. Furthermore, the dietary AX at escalating levels linearly and quadratically enhanced ( P  &lt; 0.05) the activities of serum superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and increased levels of total antioxidant capacity and reduced glutathione. In addition, malondialdehyde levels decreased significantly in AX-fed animals, and the highest levels were observed in the control group (without AX). The expression levels of  cMn-SOD ,  CAT , and  GPx  genes were significantly upregulated in the hepatopancreas of  L. vannamei  fed with AX-enriched diets (especially in the 200-mg/kg feed treatment) as compared with the control diet. The immunity indices of the AX treatments (hematocyte count, total protein, lysozyme, phagocytic activity, and phenoloxidase) of  L. vannamei  were linearly ( P  &lt; 0.05) and quadratically ( P  &lt; 0.05) increased. This study revealed the antibacterial activity of AX against  V. harveyi  abundance. After the bacterial challenge, feeding  L. vannamei  with dietary AX significantly increased ( P  &lt; 0.05) the relative percentage of survival, especially in the treatment of 200-mg/kg diet (82.7%). The findings of the current study demonstrate that dietary AX (100–200 mg/kg feed) was effective in enhancing the growth, antioxidant status, immune response, and increasing the resistance of  L. vannamei  against  V. harveyi  infection.

aquaculture international

Dietary astaxanthin modulated the performance, gastrointestinal histology, and antioxidant and immune responses and enhanced the resistance of Litopenaeus vannamei against Vibrio harveyi infection