Effects of neuropeptide Y on the immune-protection and intestinal tract of juvenile Micropterus salmoides

•NPY could affect innate immune factors of largemouth bass juveniles in both dose- and time- dependent manner.•NPY relieved intestinal damage caused by Poly I:C or LPS.•NPY alleviated the inflammatory response of juvenile largemouth bass induced by LPS or Poly I:C. Neuropeptide Y is known to be directly or indirectly involved in immune regulation. The immune effects of NPY include immune cell transport, helper T cell differentiation, cytokine secretion, staining and killer cell activity, phagocytosis and production of reactive oxygen species. In this study, we investigated the immunoprotective effect of synthetic NPY on largemouth bass larvae. For the first time, the dose and time effects of NPY injection on largemouth bass was explored, and then Poly I:C and LPS infection was carried out in juvenile largemouth bass, respectively, after the injection of NPY. The results showed that NPY could reduce the inflammatory response by inhibiting the expression of il-1β, tgf-β, ifn-γ and other immune factors in head kidney, spleen and brain, and alleviate the immune stress caused by strong inflammatory response in the early stage of infection. Meanwhile, NPY injection ameliorated the intestinal tissue damage caused by infection. This study provides a new way to protect juvenile fish and improve its innate immunity.