Dietary arachidonic acid affects the innate immunity, antioxidant capacities, intestinal health and microbiota in Chinese mitten crab (Eriocheir sinensis)

Arachidonic acid (ARA) involves in lipid metabolism, biological processes and immune response of animals. The present study aimed to evaluate the effects of ARA on the antioxidant capacity, immune response and intestinal health of Eriocheir sinensis. A 84-day feeding experiment was conducted using six isonitrogenous and isoenergetic semi-purified diets containing 0.11% (control group, G1), 1.20% (G2), 2.37% (G3), 3.52% (G4), 4.76% (G5) and 7.39% (G6) ARA of total fatty acids. Four replicates of crabs (initial body weight, 1.01 +/- 0.12 g) were fed one of the experimental diets at satiety level. Dietary ARA level did not affect the THC and phagocytic activity of crabs (P > 0.05), but RBs activity in G4 was significantly higher than that in G6 (P < 0.05). Dietary ARA significantly enhanced the activity of antioxidant enzymes, including SOD, CAT, GST and GPx (P < 0.05). For two antibacterial genes, the highest gene expression of lysozyme was found in G5 (P < 0.05), the highest gene expression of crustin was found in G5 and G6 (P < 0.05), in contrast, the moderate dietary ARA levels (1.20%-3.52% of total fatty acids) significantly inhibited their gene expression (P < 0.05). Higher dietary ARA level significantly decreased the gene expression of IL-1 beta and TNF-alpha (P < 0.05), which indicated that ARA might be linked to reduced inflammation. Furthermore, dietary ARA significantly affected the intestinal microbiota composition (P < 0.05), and the opportunistic pathogens, including Shewanella, Vibrio, Citrobacter, Candidatus_Bacilloplasma, Dysgonomonas, were enriched in the intestines of crabs fed with the lowest or highest ARA level. In conclusion, dietary ARA enhanced the antioxidant capacity, immune response and intestinal health of E. sinensis, indicating that moderate ARA supplementation in the diet could be a valuable measure towards establishing the commercial culture of crabs.