Effects of compound attractants on growth performance, feeding, intestinal development, antioxidant capacity, and immune function of Larimichthys crocea larvae

To investigate the effects of dietary compound attractants on the growth performance, appetite-related gene expression, intestinal development, antioxidant capacity, and immune function of Larimichthys crocea larvae, a compound attractant mixture was formulated using equal proportions of mogroside, vanillin, glycine, disodium inosinate, and monosodium glutamate. This compound attractant was added to a basal diet at inclusion levels of 0%, 0.01%, 0.02%, and 0.04%, resulting in four isonitrogenous and isolipidic micro-particle diets. The results showed that dietary supplementation with 0.01%, 0.02%, and 0.04% compound attractants significantly increased survival rate and specific growth rate compared with the control group. Notably, supplementation with 0.02% compound attractant significantly upregulated the mRNA expression of orexigenic genes npy and agrp, while significantly downregulating the expression of anorexigenic genes trh, cart, and lepr, indicating enhanced appetite in larvae. In addition, larvae fed diets supplemented with 0.02% and 0.04% compound attractants exhibited significantly higher activities of trypsin, α-amylase, and lipase in both pancreatic and intestinal segments. The mRNA expression levels of intestinal development-related genes zo-1, occludin, and odc were also significantly elevated. Moreover, the activities of brush border enzymes, including leucine aminopeptidase and alkaline phosphatase, were significantly increased in these groups. Furthermore, supplementation with 0.02% and 0.04% compound attractants improved antioxidant capacity by enhancing the activity of antioxidant enzymes and reducing the content of lipid peroxidation products. Notably, dietary inclusion of 0.02% compound attractant significantly elevated the levels of immune-related substances and decreased the expression of pro-inflammatory cytokine genes. In summary, dietary supplementation with 0.02% compound attractant in micro-particle diets effectively enhances appetite, intestinal development and digestion, antioxidant capacity, and immune function, ultimately improving the survival and growth performance of larvae.