An eight-week feeding trial was conducted to investigate the effects of dietary andrographolide on the growth performance, antioxidant capacity in the liver, intestinal inflammatory response and microbiota of Monopterus albus. A total of 900 health fish (25.00 ± 0.15 g) were randomly divided into five groups: AD1 (the basal diet) as the control, and AD2, AD3, AD4 and AD5 groups, which were fed the basal diet supplemented with 75, 150, 225 and 300 mg/kg andrographolide, respectively. The results showed that compared with the control group, dietary andrographolide supplementation (1) significantly increased trypsin and lipase activities in the intestine, and increased the weight gain rate but not significantly; (2) significantly increased the levels of glutathione reductase (GR), glutathione (GSH) and glutathione peroxidase (GPx) and the content of in the liver; significantly decreased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA); remarkably upregulated the Nrf2, SOD1, GSTK and GSTO mRNA levels in the liver; downregulated the Keap1 mRNA level; (3) significantly increased the villi length and goblet cell numbers in the intestine, remarkably upregulated the Occludin mRNA level in the intestine, downregulated the Claudin-15 mRNA level; (4) remarkably upregulated the IL-10, TGF-β1 and TGF-β3 mRNA levels in the intestine; downregulated the IL-12β and TLR-3 mRNA levels; (5) significantly decreased the richness and diversity of the intestinal microbioma, increased the percentages of Fusobacteria and Firmicutes and significantly decreased the percentages of Cyanobacteria and Proteobacteria. In conclusion, these results showed that dietary low-dose andrographolide (75 and 150 mg/kg) promoted growth and antioxidant capacity, regulated the intestinal microbioma, enhanced intestinal physical and immune barrier function in rice field eel.

Tributyrin (TB) has applications as a growth and intestinal health promoter for animals. A 10-week feeding trial was conducted to evaluate the application of TB to relieve the negative effects induced by high cottonseed and rapeseed meal (CRM) in juvenile grass carp (Ctenopharyngodon idellus; initial weight 9.59 ± 0.01 g). Grass carp were fed a normal fish meal (FM) diet (positive control [PC], 50 g/kg FM, 340 g/kg CRM), high CRM diet (T0, 20 g/kg FM, 540 g/kg CRM) or a T0 diet supplemented with 500 (T500), 1000 (T1000) and 1500 (T1500) mg/kg TB. The results showed that (1) grass carp fed diet T0 displayed the poorest growth (p < .05), whilst no significant differences in growth performance were observed in those fed diets PC and T1000. (2) Complement 3, glutathione peroxidase and superoxide dismutase levels in the T0 group were significantly lower (p < .05) than those in the PC group. The immune indices of fish fed the 1000 or 1500 mg/kg TB diet were significantly higher (p < .05) than those of fish fed the T0 diet, whilst there was no significant difference with PC group. (3) Compared with that of the T0 group, pro-inflammatory cytokine (il-6, il-8, nf-κb and tlr-4) expression in the 1000 mg/kg tributyrate group was significantly downregulated, whilst the expression of anti-inflammatory cytokines (il-10 and thf-β) and intestinal tight junction proteins (zo-1, zo-2, claudin-b, claudin-c and occludin) was significantly upregulated (p < .05). In conclusion, high CRM diets induced negative effects on grass carp, and dietary TB supplementation promoted growth, improved antioxidant capacity and enhanced intestinal barrier function of grass carps. And the optimum supplemental level of TB was 1000 mg/kg.

Chlorella vulgaris (C. vulgaris) powder is a novel non-grain single-cell protein with enormous potential to be a protein source. However, it is poorly studied in aquatic animals. The purpose of the present study was to explore the optimum replacement ratio of C. vulgaris powder and the influence of the substitution of soybean meal with C. vulgaris on grass carp (Ctenopharyngodon idella) in terms of growth performance, intestinal integrity and the microbial community. Five isonitrogenous and isolipidic diets were formulated by replacing 0% (SM, containing 30% soybean meal), 25% (X25), 50% (X50), 75% (X75) and 100% (X100) soybean meal with C. vulgaris. The feeding trial period lasted 8 weeks. At the end of the experimental trial, the X50 group showed higher FW, WGR and PER than the SM group (p < 0.05). The feed conversion ratio (FCR) of the X50 group was significantly lower than that of the SM group (p < 0.05). The X50 group showed the highest value of the goblet cell number, intestinal amylase and trypsin activities when compared with the SM group (p < 0.05). Replacing 50% soybean meal with C. vulgaris improved the intestinal barrier integrity, as evidenced by upregulating zo-1, zo-2 and occluding transcript (p < 0.05), and alleviated oxidative stress by an increased SOD enzymatic activity and transcript level, probably mediated through the Nrf2-keap1 signaling pathway (p < 0.05). Meanwhile, the X50 group enhanced intestinal immunity, as manifested by increased ACP and LZM activities (p < 0.05), and downregulated the tlr-4, tlr-7, tlr-8 and il-6 through the tlr pathway (p < 0.05). The functionally predicting pathways related to the nitrate respiration and nitrogen respiration were observably activated in the X50 group (p < 0.05). The X50 group improved the biological barrier, as manifested by increased Firmicutes and Rhodobacter (p < 0.05). In conclusion, dietary C. vulgaris powder could promote the growth performance of grass carp by restoring intestinal morphology, increasing digestive enzyme activities, improving antioxidant properties and immunity and optimizing the microflora structure. A C. vulgaris powder replacement of 50% soybean meal was recommended as feed for grass carp.

Imidacloprid (IMI), a widely used neonicotinoid insecticide, has raised environmental concerns due to its potential impact on non-target aquatic organisms. This study investigates the effects of IMI exposure on the intestinal immune function of red swamp crayfish (Procambarus clarkii, P. clarkii), focusing on oxidative stress, inflammatory response, and autophagy. The P. clarkii was exposed to different doses of IMI (0, 10.93, 21.86, 43.73, 87.45 μg/L) for 96 h. Our findings reveal that IMI exposure leads to a survival rate of less than 70% when the concentration was 87.45 μg/L at 96 h. Hemolymph LZM and AKP contents were significantly decreased at the medium and high concentrations, and the expressions of hsp70 and nf-κb genes were significantly up-regulated. The expression of the lysozyme gene was significantly down-regulated. Additionally, the activities of SOD, CAT, and GPX were significantly decreased, the contents of MDA were significantly increased, and the gene expressions of CuZnsod, mMnsod, cat, and gpx in the gut were significantly down-regulated after exposure to medium-high IMI. The expression of autophagy-related genes showed that the expressions of beclin1, atg5, atg13, and lc3c genes in the medium- and high-concentration groups were significantly up-regulated. In summary, this study elucidates that medium-high levels of IMI exposure impair intestinal immune function in P. clarkii through mechanisms involving oxidative stress, inflammatory response, and autophagy.