Role of sodium octanoate in regulating survival, growth, intestinal development, digestive and absorptive capacities, antioxidant capacity and innate immunity of large yellow croaker (Larimichthys crocea) larvae

The present study was conducted to investigate the effects of dietary sodium octanoate (So) on the survival, growth, intestinal development, digestive and absorptive capacities, antioxidant capacity and innate immunity of Larimichthys crocea larvae. Larvae (initial body weight: 7.44 ± 0.53 mg) were fed with either a control diet or diets with different levels (0.1%, 0.2%, 0.4%, and 0.8%) of So for 30 days. The results showed that larvae fed diets with 0.1%–0.4% So had significantly increased survival compared to the control. Compared to the control, larvae fed the diet with 0.4% So showed dramatically improved growth performance, although there were no significant differences between other diets. Notably, larvae fed diets with 0.2%–0.4% So displayed significantly higher fold height of intestine compared to the control group. Increased levels of selected intestinal cell proliferation and differentiation gene markers (pcna and odc) and increased activity of intestinal brush border enzymes (alkaline phosphatase and leucine aminopeptidase) further affirmed the promotional effect of So on intestinal development. Moreover, for genes related to the intestinal apical junction complex, larvae fed diets with 0.1%–0.8% So showed significantly higher mRNA expression levels of occludin and cateninα1 than the control group. Meanwhile, compared to the control, the expression of claudin1, afadin and cadherin2 significantly increased in larvae fed diets with 0.1%–0.4% So. Also, larvae fed diets with 0.1%–0.8% So showed significantly higher activity of lipase than the control group, whereas the activity of trypsin was significantly higher only in larvae fed the diet with 0.4% So. Furthermore, absorption capacity, as reflected by the activity of brush border enzymes (Na+-K+-Adenosinetriphosphatase and creatine kinase), significantly increased in larvae fed diets with 0.2%–0.4% So compared to the control. Furthermore, larvae fed the diet with 0.4% So exhibited improved antioxidant enzyme activity (catalase and total antioxidant capacity), upregulated antioxidant related gene expression (sod2, sod3, cat, and nrf2), increased antioxidant substance levels (reduced glutathione), and decreased malondialdehyde content compared to the control group. Moreover, larvae fed the diet with 0.4% So showed the highest activity of innate immune-related enzymes (lysozyme, acid phosphatase, inducible nitric oxide synthase and total nitric oxide synthase) and the highest mRNA expression of anti-inflammatory cytokines (il4/13 and arg1). In summary, the diet supplemented with 0.4% So may optimally improve larval survival and growth probably by enhancing intestinal development, digestion and absorption, antioxidant capacity, and innate immunity.