Effects of dietary β-glucan, mannan oligosaccharide and their combinations on growth performance, immunity and resistance against Vibrio splendidus of sea cucumber, Apostichopus japonicus

A 4-week feeding trial was conducted to investigate the effects of dietary β-glucan, mannan oligosaccharide (MOS) and their combinations on growth performance, immunity and disease resistance of sea cucumber Apostichopus japonicus. Sea cucumbers (1215 individuals with initial weight of 3.8 ± 0.2 g) were fed nine practical diets according to a 3 × 3 factorial design: the basal diet as the control supplemented with three levels of β-glucan (0, 0.075, 0.15% w/w), crossed with 0, 0.1% (w/w) or 0.2% (w/w) MOS. Immune indices including total coelomocytes count (TCC), phagocytosis, superoxide anion production, superoxide dismutase (SOD) activity and total nitric oxide synthase activity (T-NOS) were measured at days 7, 11, 15, 18, 22, 25 and 29. At the end of the feeding trial, all the sea cucumbers left were weighted to monitor growth, and then were challenged by Vibrio splendidus. The results showed that dietary β-glucan, MOS and their combinations significantly increased TCC, phagocytosis, superoxide anion production and SOD activity of sea cucumbers (P < 0.05). Only 0.15% β-glucan and the combinations of β-glucan and MOS significantly increased the T-NOS activity (P < 0.05). A synergistic effect was found between dietary β-glucan and MOS. Moreover, combinations of β-glucan and MOS prolonged the high levels of immune indices compared with β-glucan or MOS supplementation alone. Except the 0.15% β-glucan group, all the other treatments showed significantly lower cumulative mortality compared with control (P < 0.05). Furthermore, combination of 0.15% β-glucan and 0.1% MOS had the best effects on enhancing disease resistance of sea cucumber. All treatments showed significantly higher specific growth rate (SGR) compared with control (P < 0.05), and the combination of 0.15% β-glucan and 0.1% MOS was significantly higher than other treatments (P < 0.05). In conclusion, our results confirm the potential of β-glucan and MOS as dietary immunostimulants and the synergistic effects of β-glucan and MOS on A. japonicus.