Effects of dietary lipid levels on antioxidant capacity, inflammatory response and endoplasmic reticulum stress in immune organ of turbot (Scophthalmus maximus L.)

Lipid, one of the most important macronutrients of organism, can provide energy and essential fatty acids for aquatic animals. Excessive lipid level in diet has negative effects on fish health. However, the regulation mechanism of lipid level on the immunity of marine fish is still not completely understood. Therefore, a 56-day feeding trial was conducted to evaluate the effects of dietary lipid levels on antioxidant capacity, inflammatory response and endoplasmic reticulum stress in immune organs of turbot (Scophthalmus maximus L.). Turbot (9.87 ± 0.13 g) were fed a diet with a low (lipid 6 %, L6), medium (lipid 12 %, L12) and high (lipid 18 %, L18) crude lipid content. Results showed that the L18 group significantly reduced the survival rate during the V. harveyi challenge test compared with L6 and L12 groups. The respiratory burst activity, lysozyme (LZM) and alkaline phosphatase (AKP) in serum were significantly decreased in L6 and L18 groups. Moreover, the L18 group significantly decreased the T-AOC, superoxide dismutase (SOD) and catalase (CAT) activities in head kidney and spleen than that in the L12 group, while the malondialdehyde (MDA) content had no significant changes. Furthermore, the L18 group significantly upregulated the pro-inflammatory genes (tnf-α, il-1β, ifn-γ, p65 and caspase7) expression and the phosphorylation level of the c-Jun N-terminal kinase (JNK) - Mitogen-activated protein kinase (MAPK) pathway in head kidney. Similarly, in spleen, the pro-inflammatory genes (il-1β, ifn-γ, p65 and caspase7) expression were also significantly upregulated in the L18 group. In addition, the endoplasmic reticulum (ER) stress related genes and proteins expression in head kidney and spleen were also significantly upregulated in the L18 group. Overall, these results revealed that the high lipid level in diet suppressed antioxidant capacity and induced inflammatory response of turbot. This study could advance the understanding of effects of dietary lipid levels on turbot (Scophthalmus maximus L.) and improve the utilization rate of high-fat diets in aquaculture.