Effects of dietary mannan oligosaccharide supplementation on growth performance, antioxidant capacity, non-specific immunity and immune-related gene expression of juvenile hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

Abstract

The present study was conducted to investigate the effects of dietary mannan oligosaccharide (MOS) supplementation on growth performance, antioxidant capacity, non-specific immunity and immune-related gene expression in juvenile hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀). A basal diet supplemented with MOS (0, 0.3%, 0.6%, 1.0% and 2.0%) was fed to juvenile hybrid grouper for 9 weeks. Results showed that there were no significant differences in feed intake, hepatosomatic index, spleen index or survival among all groups (P > .05). However, antioxidant analyses showed that hybrid grouper fed with MOS supplementation had significantly enhanced total antioxidant capacity (T-AOC) and superoxide dismutase (SOD). Non-specific immunity evaluation showed that hybrid grouper fed with MOS supplementation had significantly enhanced respiratory burst activity (RB), acid phosphatase activity (ACP) and lysozyme activity (LZM) (P < .05). Moreover, dietary MOS supplementation also enhanced morphological integrity of intestine (muscle thickness, villus length and villus width) (P < .05). Furthermore, in the intestine and liver of juvenile hybrid grouper fed dietary MOS, expression of immune-related genes Interleukin 8 (IL-8), Transforming growth factor β1 (TGF-β1), Target of rapamycin (TOR) and Toll-like receptor 3 (TLR3) was upregulated, whereas Kelch-like-ECH-associated protein 1 (Keap1), IκB kinase α (IKKα) and the apoptosis-related genes (p53 and Caspase-3) were down-regulated. After challenge with Vibrio harveyi, significantly higher post-challenge survival rate was observed in 0.6% MOS supplemented group than the control group (P < .05). These results indicate that dietary MOS supplementation does not improve growth performance or feed utilization of juvenile hybrid grouper; however, it can promote intestinal health and immunological status—by improving intestinal morphological integrity, enhancing antioxidant capacity and non-specific immunity, increasing immune-related gene expression and decreasing apoptosis-related gene expression in the intestine and liver.