This trial was conducted to investigate the effect of mannose oligosaccharides (MOS) on the growth performance, antioxidation, immunity and disease resistance of Vibro Parahemolyticus in juvenile abalone Haliotis discus hannai Ino. Four formulated diets were produced to contain 0.00 g/kg, 0.40 g/kg, 0.80 g/kg and 1.60 g/kg Actigen®, with functional ingredients of MOS, respectively. Accordingly, the experimental diets were named as A0, A4, A8 and A16. After 120-days feeding trial, the best growth performance was observed in A8 group (P < 0.05) and there was no significant difference in A0, A4 and A16 groups. With the increase of dietary MOS, the activity of the total antioxidant capacity in hepatopancreas is increasingly elevated (P < 0.05) while no significant difference was observed on activity of glutathione S-transferase (P > 0.05). The activities of superoxide dismutase and glutathione peroxidase were firstly increased and then decreased, with the highest values in A8 group (P < 0.05). Immune-related parameters were significantly affected by dietary MOS inclusion. Specifically, the activities of alkaline phosphatase and acid phosphatase in hepatopancreas and serum of abalone fed diets containing MOS were significantly higher than those of control A0 group (P < 0.05). Moreover, the highest values of both enzymes were observed in hepatopancreas of A8 group but in serum of A16 group, respectively. The lysozyme activities in hepatopancreas and serum of A4 group were significantly higher than those of other groups (P < 0.05) and there was no significant difference in A0, A8 and A16 groups (P > 0.05). The activities of cytophagy and respiratory burst in serum of abalone were not significantly affected by dietary MOS content (P > 0.05). The mRNA levels of focal adhesion kinase and integrin-linked kinase were gradually elevated with the increase of dietary MOS, with the highest value recorded in A16 group (P < 0.05). The gene expression of caspse-3 in A8 group was dramatically higher than those of other groups (P < 0.05) and there was no significant difference in A0, A4 and A16 groups (P > 0.05). The mRNA level of nuclear factor-κB was not significantly affected by dietary MOS (P > 0.05). During 56 h of V. Parahemolyticus challenge period, the accumulated mortality rate of abalone fed diets containing MOS were significantly lower than that of control A0 group in each time point (P < 0.05). Overall, the lowest rate was happened in A8 group (P < 0.05). In conclusion, MOS inclusion in diet has obviously positive effect on growth, immunity and disease resistance capability of abalone, with the optimal level of Actigen® at 0.80 g/kg in diet.

In the present study, a sialic acid-binding lectin was identified and characterized from Manila clam Ruditapes philippinarum (designed as RpSABL-1). Multiple alignments strongly suggested that RpSABL-1 was a new member of the sialic acid-binding lectin family. In non-stimulated clams, RpSABL-1 transcripts were constitutively expressed in all five tested tissues, especially in hepatopancreas. After Vibrio anguillarum challenge, the expression of RpSABL-1 mRNA was significantly up-regulated at 6 h (P < 0.05), 12 h (P < 0.01) and 24 h (P < 0.01). Recombinant RpSABL-1 protein (rRpSABL-1) displayed apparent binding activities towards lipopolysaccharides (LPS) and peptidoglycan (PGN), but not to glucan or chitin in vitro. Coinciding with the PAMPs binding assay, rRpSABL-1 exhibited obvious agglutination activities against Gram-positive bacterium Staphyloccocus aureus, Gram-negative bacteria Escherichia coli, V. anguillarum and Vibrio harveyi. Meanwhile, rRpSABL-1 showed antibacterial activities against E. coli, and biofilm formation of E. coli could also be inhibited after incubated with rRpSABL-1. Moreover, the encapsulation, phagocytosis and chemotactic ability of hemocytes could be enhanced by rRpSABL-1. All these results suggested that RpSABL-1 could function as a pattern recognition receptor with versatile functions in the innate immune responses of R. philippinarum.