Microorganisms play crucial roles in nutrient cycling, water quality maintenance, and farmed animal health. Increasing evidences have revealed a close association between unstable microbial environments and disease occurrences in aquaculture. Thereupon, we used high-throughput sequencing technology to comprehensively compare the bacterial communities of water, sediment, and intestine in mariculture ponds at the middle and late stages of Litopenaeus vannamei farming and analyzed whether changes of their microbiota assemblages were associated with environmental factors and shrimp physiological health. Results showed that bacterial community structures were significantly distinct among water, sediment, and intestine; meanwhile, the relative abundances of intestinal dominant taxa were significantly changed between different rearing stages. Compared with intestine and water, shrimp intestine and sediment had a similar profile of the dominant bacterial genera by cluster analysis, and the observed species, diversity indexes, and shared OTUs of bacterial communities in intestine and sediment were simultaneously increased after shrimp were farmed for 90 days. These results reflected a closer relationship between microbiotas in sediment and intestine, which was further proved by nonmetric multidimensional scaling analysis. However, bacterial communities in water, sediment, and intestine responded differently to environmental variables by redundancy and correlation analysis. More importantly, shrimp physiological parameters were closely associated with bacterial variations in the gut and/or ambient, especially the gut microbiota owning significantly high levels of predicted functional pathways involved in disease emergence. These findings may greatly add to our understanding of the microbiota characteristics of the shrimp pond ecosystem and the complex interactions among shrimp, ambient microflora, and environmental variables.

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In this study, a feeding trial followed by a challenge test was performed to evaluate effects of six herbal formulae which were different combinations of Astragalus polysaccharides (APS), chlorogenic acid (CGA) and allicin on growth performance, non-specific immune response, antioxidant capacity, disease resistance and biomolecule damage of white shrimp Litopenaeus vannamei. Shrimp were fed seven diets, control diet (basal diet with no herbal formulae) and six herbal formula diets (G1-G6, basal diet supplemented with 0.1% APS + 0.05% allicin, 0.1% APS + 0.1% allicin, 0.1% CGA + 0.05% allicin, 0.1% CGA + 0. 1% allicin, 0.1% APS + 0.1% CGA and 0.1% APS + 0.1% CGA + 0.05% allicin respectively), for 21 days. After that, shrimp were challenged with Vibrio harveyi and then the cumulative mortality of shrimp was recorded for 7 days post challenge. The results showed that there were no significant differences in growth performance among all groups, while the nonspecific immune responses and antioxidant indexes were significantly improved (p < .05) in shrimp fed herbal formula diets when compared to the control. Meanwhile, the lowest cumulative mortality was observed in shrimp fed herbal formula diets with 0.1% APS, 0.1% CGA and 0.05% allicin supplementation after V. harveyi challenge. Additionally, herbal formulae could not cause biomolecule damage to the hepatopancreas of shrimp. In conclusion, these results indicated that synergistic effect of APS, CGA and allicin helped to boost immunity, antioxidant capacity and disease resistance of shrimp without biomolecule damage. K E Y W O R D S antioxidant status, biomolecule damage, herbal formulae, Litopenaeus vannamei, non-specific immune response, vibriosis resistance

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