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. <i>Haematococcus pluvialis</i> is one of the most important sources of natural astaxanthin. In this 8-week feeding experiment, the impacts of gradient additions of <i>H. pluvialis</i> on the growth and physiological performance of <i>Litopenaeus vannamei</i> 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 <i>H. pluvialis</i> 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 (<i>P</i> < 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 <i>H. pluvialis</i> is maximized at an inclusion level of 0.1006%. The acute ammonia stress test revealed that the addition of <i>H. pluvialis</i> significantly ameliorated the morphology and structure of hepatopancreas in D0.08, D0.16 and D0.32 groups (<i>P</i> < 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 <i>H. pluvialis</i>. The expression levels of <i>ho1</i> and <i>sod</i> mRNA in the D0.08 group increased after stress, indicating upregulation of antioxidant and immune-related genes (<i>P</i> < 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 (<i>P</i> < 0.05). After stress, <i>crustin</i> was down-regulated significantly in the <i>H. pluvialis</i> supplemental groups, while <i>tube</i> and <i>relish</i> mRNA expression levels were significantly higher in the D0.32 group compared to the D0 group (<i>P</i> < 0.05). The results demonstrated that the growth performance of <i>L. vannamei</i> was enhanced by incorporating 0.02% to 0.08% of <i>H</i>. <i>pluvialis</i> into the diet. Furthermore, dietary supplementation with 0.08% to 0.32% resulted in an increased resistance to ammonia nitrogen stress in <i>L. vannamei</i>.