Abstract:A 60-d feeding experiment was conducted to investigate the effects of basic diet with four different additives of yeast polysaccharide(6. 3 g/kg), Paracoccus marcusii(109 cfu/kg), rhubarb(Rhei Radix et Rhizoma, 25. 0 g/kg)and florfenicol(15. 0 mg/kg)on non-specific immunity and expression of intestinal immune gene(Aj-p105, Aj-p50, Aj-rel and Aj-lys)in sea cucumber[Apostichopus japonicus, mean initial body weight(4. 6 8± 0. 36)g]. Five groups of sea cucumbers were fed with the basal diet(control group), basal diet with yeast polysaccharide, P. marcusii, rhubarb, and florfenicol supplementation, respectively. Each diet was randomly fed to five tanks at a density of 10 sea cucumbers per tank. The results showed that the phagocytosis and respiratory burst activities of the coelomocytes of sea cucumber fed diets with P. marcusii supplementation were significantly higher than those in the control group. Dietary yeast polysaccharide supplementation significantly enhanced the phagocytosis activity of the coelomocytes compared with the control group. However, the respiratory burst activity of the coelomocytes in the florfenicol group was significantly lower than that in the control group. At transcriptional level, the relative expression of Aj-p105 and Aj-p50 genes in mid-intestine tissue of sea cucumber in yeast polysaccharide and P. marcusii groups were significantly higher than those in the control group with increase of 43. 2% and 63. 1% in yeast polysaccharide group, and with increase of 49. 8% and 48% in P. marcusii group, respectively. The relative expression of Aj-lys gene in P. marcusii group was significantly higher than that in the control group with an increase of 46. 4%. The relative expression of Aj-p105 in rhubarb group was significantly higher than that in the control group. While the expression of Aj-p50, Aj-rel and Aj-lys genes in mid-intestine of sea cucumber in florfenicol group was significantly decreased compared to the control group. In summary, these results suggested that dietary yeast polysaccharide and P. marcusii would enhance the non-specific immunity of sea cucumber, but feeding florfenicol may have an opposite effect.