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At present, peptidoglycan (PGN) is commonly used as an immunostimulant in shrimp. However, little has been known about its mechanism. In this study, comparative transcriptome analysis was employed to investigate the impact of dietary PGN on the immune response in Litopenaeus vannamei. A total of 720 healthy juvenile L. vannamei (initial weight 0.31 ± 0.05 g) were randomly evenly allocated to 18 fibreglass buckets as 6 groups, fed with six isonitrogen (41.05%) and isolipid diets (8.16%) containing PGN at the doses of 0 (control), 0.2, 1, 5, 25, and 125 mg/kg, respectively. After 8 weeks feeding trail, the growth performance, immunity, and transcriptome response of L. vannamei were analyzed. The results showed that the growth performance of L. vannamei was not significantly influenced by dietary PGN (P > 0.05). According to the analysis of weight gain rate (WGR), the optimum dietary PGN level was 71.46 mg/kg. Compared with the control group, the survival rate (SR) after Vibrio parahaemolyticus infection of L. vannamei were significantly increased by dietary PGN at 5 mg/kg and the SR after white spot syndrome virus (WSSV) infection was improved by dietary PGN at 25 mg/kg (P

The type of protein source in diets has many effects on shrimp. In this study, Litopenaeus vannamei with an initial body weight of 3.68 ± 0.002 g were fed for 8 weeks on three experimental diets (isoproteic: 41.00%; isolipidic: 7.61%) that were formulated using fish meal (FM), Chlorella sorokiniana (CHL), and Clostridium autoethanogenum protein (CAP) as the primary protein sources, respectively. This study examined the growth, non-specific immunity, intestinal digestion, and microbiota of L. vannamei after the feeding experiment concluded. Compared to the FM group, the findings indicate that the weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) of L. vannamei were notably enhanced via dietary CAP. The CHL group exhibited the highest levels of catalase (CAT), phenoloxidase (PO), and superoxide dismutase (SOD) activities in the gills of L. vannamei, whereas the FM group had the lowest levels. Conversely, the malondialdehyde (MDA) content showed the opposite trend. Both dietary CHL and CAP promoted the digestive enzyme activities of L. vannamei, with dietary CAP having a more pronounced promotional effect. An analysis of alpha diversity indicated that the consumption of dietary CHL substantially enhanced the abundance and diversity of microbiota in the intestinal tract of L. vannamei. Furthermore, the dietary CHL significantly increased the colonization of immune-associated beneficial bacteria and inhibited the colonization of pathogenic bacteria in the intestinal tract of L. vannamei, whereas dietary CAP mainly increased the colonization of growth-associated beneficial bacteria. Functional predictions showed that different dietary protein sources affect various metabolic activities and signaling pathways of L. vannamei, and some functions, including signal transduction, cell motility, and the immune system, were significantly enhanced in the CHL group. In summary, both dietary CHL and dietary CAP promoted growth and immunity in L. vannamei compared to dietary FM. The results of this study could be helpful for the sustainable development of shrimp farming.

The effects of dietary zymosan A on the growth performance and histological structure, digestive capacity, and microbiota were investigated in Litopenaeus vannamei, an important shrimp species used in aquaculture. L. vannamei (initial body weight = 0.41 ± 0.05 g) were fed diets supplemented with zymosan-A at doses of 0 mg/kg (Z0, control), 1 mg/kg (Z1), 5 mg/kg (Z5), 25 mg/kg (Z25), 125 mg/kg (Z125), or 625 mg/kg (Z625) for 8 weeks. The results showed that doses of 25 and 125 mg/kg significantly increased the final body weight, weight gain rate (WGR), and specific growth rate (SGR) and significantly decreased the feed conversion rate compared with the controls (p < 0.05). Analyses of the WGR and SGR revealed that the optimum dietary zymosan-A levels were 308.56 and 300.00 mg/kg, respectively. Compared with the controls, the intestinal villus height was significantly increased by the addition of zymosan-A at doses ≥25 mg/kg (p < 0.05). An obvious upregulation of the activities of trypsin and amylase was observed in all groups that received zymosan-A supplementation, while the activity of lipase was significantly increased in groups Z125 and Z625 (p < 0.05). Consistently, the gene expressions of trypsin and lipase were significantly higher in group Z125, while the gene expression of amylase was significantly increased in all zymosan-A-supplemented groups (p < 0.05). Analysis of the intestinal microbiota showed significant differences in the alpha diversity between group Z125 and controls. The supplemented groups showed altered intestinal bacterial community structures and compositions at the phylum, family, and genus levels, with statistical differences observed in the relative abundances of some dominant species. Tax4Fun predictions of the microbiota indicated that multiple intestinal functions were significantly altered in all zymosan-A-supplemented groups, except Z1. Among these groups, the functions related to transport and catabolism, substance dependence, cardiovascular disease, and signaling molecules and interactions were obviously increased by the addition of zymosan-A at different levels. In conclusion, dietary supplementation of the optimum amount of zymosan-A can improve growth and intestinal function in L. vannamei, which will be valuable in aquaculture.

Biochemical fulvic acid (BFA), produced by organic wastes composting, is the complex organic matter with various functional groups. A novel modified biochemical fulvic acid (MBFA) which possessed stronger chelating ability had been synthesized by the grafting copolymerization of BFA and acrylic acid (AA). Results showed that MBFA effectively inhibited the crystallization of calcium phosphate and increased the concentration of phosphate in water solution. The optimum reaction conditions optimized by Box–Behnken design and response surface methodology were reaction temperature 69.24 °C, the mass of monomer to fulvic acid ratio 0.713, the initiator dosage 19.78%, and phosphate crystal-inhibition extent was 96.89%. IR spectra demonstrated AA was grafted onto BFA. XRD data and SEM images appeared the formation and growth of calcium phosphate crystals was effectively inhibited by MBFA.