LAUSR

This study was conducted to investigate the effects of dietary β-conglycinin on the growth performance, digestion, gut morphology and immune responses of juvenile turbot (Scophthalmus maximus L.). Four diets were formulated to contain 0%, 2%, 4% and 8% purified β-conglycinin. Triplicate groups of 30 fish were fed to apparent satiation twice daily for 12 weeks. Fish fed 4% and 8% dietary β-conglycinin showed significantly reduced specific growth rate, feed efficiency ratio, apparent digestibility coefficient of nutrients and whole-body lipid contents, as well as a profound infiltration of mixed leucocytes in the lamina propria and a significant decrease in the absorptive surface of distal intestine. The expression of pro-inflammatory cytokines, TNF-α and IL-1β, in the distal intestine was significantly upregulated by 4% dietary β-conglycinin, whereas a significantly lower expression level of IgM and anti-inflammatory cytokine TGF-β1 was observed in fish fed 8% dietary β-conglycinin. Serum lysozyme and alternative complement pathway activity were first significantly enhanced by 2% dietary β-conglycinin and then rapidly declined by 4% and 8% dietary β-conglycinin. Respiratory burst activity of head kidney macrophages and serum superoxide dismutase activity were significantly suppressed by 4% and 8% dietary β-conglycinin. Dietary β-conglycinin (2–8%) significantly increased the level of specific antibody against β-conglycinin in serum. Collectively, these results suggested that higher levels of dietary β-conglycinin (4–8%) induced a variety of non-specific and specific immune responses and intestinal mucosal lesions in turbot, resulting in inferior feed utilization and poor growth performance.