Interactive effects of dietary vegetable oil and carbohydrate incorporation on the innate immune response of European seabass (Dicentrarchus labrax) juveniles subjected to acute stress

This study aims to understand the interactive effects of high dietary vegetable oils (VO) and carbohydrate (CH) content in European seabass cellular, humoral, and molecular innate immune responses to an acute stress. For that purpose, European sea bass juveniles (74.0 ± 1.5 g) were fed four diets differing in lipid source (fish oil (FO) or a blend of vegetable oils (VO)) and carbohydrate content (0% (CH-) or 20% (CH+) gelatinized starch). Nine fish per dietary treatment were sampled after 73 days of feeding and used as control whereas the remaining fish were subjected to an acute stress (netting, 1 min air exposure, and transfer to smaller tanks). Those fish were then sampled after 1 h and considered the stressed group. In the present study, dietary VO incorporation affected fish humoral immune parameters with a decrease of haematocrit, plasma peroxidase activity, and head-kidney mc2r and gr1 mRNA expression levels. Regardless of dietary treatment, higher cortisol levels were accompanied by an increase of several haematological, cellular, and humoral parameters in response to an acute stress. Dietary VO incorporation led to lower neutrophil numbers, plasma antiproteases activity, and head-kidney cox2 expression level in stressed fish. Fish fed CH+ diets showed a reduction of head-kidney mc2r expression levels in response to stress, while plasma cortisol remained unchanged, plasma NO decreases and antiproteases activity increased. In fish fed the VO diets, CH+ led to a decrease of plasma bactericidal activity compared to that of group CH-, while the opposite pattern was observed for plasma peroxidase. In conclusion, dietary substitution of FO by VO in CH- diet negatively affected the immune response in both undisturbed and stressed fish, while the effect of dietary CH incorporation in VO diet was not clear.