Effects Of Dietary Supplementation Recombined Ptalf8 Protein (Rptalf8) On The Growth Performance, Antioxidant Capacity And Gut Microbial Composition In Swimming Crab, Portunus Trituberculatus

An 8 weeks feeding trial was performed to determine the effects of dietary supplementation with rPtALF8 on the growth performance, antioxidant capacity and gut microbial composition in Portunus trituberculatus. Four experimental diets were carried out with addition of 0 (control), 10 (D10), 20 (D20), and 40 (D40) mg kg(-1) rPtALF8 in diet. Three hundred and sixty crabs were randomly divided into four groups and each group contained three replicates. No significant difference was found in survival rate in each group (P > 0.05). Weight gain rate (WGR) and specific growth rate (SGR) in the D20 group were significantly higher than control group (P < 0.05). The activity of LZM in D10 and D20 groups were significantly higher than control group (P < 0.05), but there was no significant difference found between D10 and D20 group (P > 0.05). While rPtALF8 was added at 20 mg kg(-1) in diet, the activity of ACP in the plasma reached the highest, significantly higher than that in the other groups (P < 0.05). In the D20 group, the T-AOC levels and the activity of SOD in the hepatopancreas were increased significantly (P < 0.05), whereas the MDA level was significantly lower than other three groups (P < 0.05). After being challenged with Vibrio alginolyticus, the cumulative mortality of D20 group and D40 group at 6 h and 12 h was significantly lower than that of the control group (P < 0.05). At 18 h and 24 h, the cumulative mortality rate of the D20 group was significantly lower than that of the control group (P < 0.05). However, no significant difference was detected between D40 and control groups (P > 0.05). In terms of gut microbiota, rPtALF8 could significantly affect the alpha-diversity and community composition of intestinal bacteria of P. trituberculatus. Proteobacteria, Bacteroidetes, and Firmicutes were the dominant bacteria in the gut of P. trituberculatus among groups. Highest relative abundance of Proteobacteria and lowest relative abundance of Firmicutes were observed in D40 group. Besides, supplementation of rPtALF8 in diet also significantly decrease the relative abundance of Thermobifida and Saccharomonospora. The results indicated that dietary supplementation with 20-40 mg kg(-1) rPtALF8 could improve the WGR and SGR, enhance the antioxidant capacity and innate immunity of P. trituberculatus. In conclusion, rPtALF8 can be used as a novel antibiotic substitute in P. trituberculatus farming.