The Effects Of YSP On The Immune Function Of Penaeus Vannamei

The whole experiment is divided into two parts. The first part is to study the effect of yeast (Saccharomyces cerevisiae ) polysaccharide(YSP) on the immune syste-m of Penaeus vannamei. Among a series of does of polysaccharides (0.1%, 0.2%,0.5%, 0.8%, 1%), activity of PO and the total protein content(PC) in serum, activity of SOD in muscle and the level of ·02- were measured respectively at different stage. After two week, the activity of PO was enhanced by 36%, 170%, 150%, 170% in the groups of 0.2%, 0.5%, 0.8% and 1%, but on the 21st day , the activity of PO in all groups except the group of 0.1%, decreased to the level the same as the non-supplement group polysaccharide. The activity of SOD in the muscle was enhanced by 260%, 670 %, 300% in the groups of 0.5%, 0.8% and 1%, in addition, the change of ·02- was not significant after one week. The activity of SOD in the high does groups remained a high level and PO reached the max after two week, but after three week they have already brought dwon,·02- in the gro-oups of 0.8% and 1% reached to the maximum. Therefore, it is induced that the over-does polysaccharide (1%) may destroy the dynamic equilibrium between active oxygen and SOD in shrimp. The effects of the low does (0,1%, 0.2%) polysaccharide is not significant. According to the experiment result, we advise that a feasible does be 0.5% to 0. 8% and polysaccharide be fed for one or two week then have a break for one week.The second part is the determination of the effects of polysaccharide on PO, SOD, PC and ·02- when suffered salinity and pH stress in 24h. The result showed that there are enhancements of ·02- and PC decreased after stress, but polysaccharide can affect the activity of PO and SOD in some degree, as well increase the level of protein in serum. Polysaccharide is an effective immunostimulat and it can increase the resistance to stress inPenaeus vannamei.