Effects of Haematococcus pluvialis on growth performance, hepatopancreatic transcriptome and resistance to ammonia-nitrogen stress of pacific white shrimp (Litopenaeus vannamei).

Astaxanthin is widely used in aquatic animal feed and has beneficial effects on aquatic animals. Haematococcus pluvialis is one of the most important sources of natural astaxanthin. In this 8-week feeding experiment, the impacts of gradient additions of H. pluvialis on the growth and physiological performance of Litopenaeus vannamei before and after acute ammonia nitrogen stress were investigated. The experimental diets were formulated by incorporating gradient levels (0%, 0.02%, 0.04%, 0.08%, 0.16% and 0.32%) of H. pluvialis into the feed, namely D0, D0.02, D0.04, D0.08, D0.16 and D0.32, respectively. Each tank housed 30 shrimp, with 4 replicates per group. Significant improvements were observed in weight gain and specific growth rate (P < 0.05) in D0.02, D0.04 and D0.08 groups compared with the control group D0. Regression curve analysis indicated that the growth effect of H. pluvialis is maximized at an inclusion level of 0.1006%. The acute ammonia stress test revealed that the addition of H. pluvialis significantly ameliorated the morphology and structure of hepatopancreas in D0.08, D0.16 and D0.32 groups (P < 0.05), while attenuating the apoptosis signal in hepatopancreatic cells, thereby indicating a potential alleviation of liver injury and cellular apoptosis induced by acute ammonia stress through the incorporation of a specific proportion of H. pluvialis. The expression levels of ho1 and sod mRNA in the D0.08 group increased after stress, indicating upregulation of antioxidant and immune-related genes (P < 0.05). As compared to the control group, the Toll pathway genes exhibited significantly higher expression levels in diets D0.02 and D0.04 prior to stress (P < 0.05). After stress, crustin was down-regulated significantly in the H. pluvialis supplemental groups, while tube and relish mRNA expression levels were significantly higher in the D0.32 group compared to the D0 group (P < 0.05). The results demonstrated that the growth performance of L. vannamei was enhanced by incorporating 0.02% to 0.08% of H. pluvialis into the diet. Furthermore, dietary supplementation with 0.08% to 0.32% resulted in an increased resistance to ammonia nitrogen stress in L. vannamei.