Effects Of Dietary Chitosan Oligosacchairde, Rare Eatrh Elements And Its Complex With Chitosan Oligosaccharide On The Growth, Immune Response And Resistance Against Vibrio Splendidus Infection Of Sea Cucumber

The sea cucumber Apostichopus japonicus(Selenka) has been recognized as one ofthe commercially important holothurian species. To date, sea cucumber has been widelycultured in northern China because of increasing demand and on the verge of exhaustionof natural resources. However as intensive aquaculture expanded and heavy debates ofantibiotic performance enhancers, causing huge economically losses and constraint toexpansion of this industry. Thus, efficient use of available resources is required. Thiswork was conducted to study the effect of dietary chitosan oligosaccharide, rare earthnitrate and its complex with chitosan oligosaccharide（COS-Ree）supplementation ongrowth, immune response and disease resistance of sea cucumber. The results arefollows.1.The present study was conducted to determine the effect of dietary chitosanoligosaccharide (COS) on the growth, immune response and resistance against Vibriosplendidus infection of sea cucumber. The basal diet was supplemented with0%,0.25%,0.50%,1.00%and2.00%COS to formulate five experimental diets. After thefeeding trial, a V. splendidus injection challenge was executed to test the effect of COS.The results of8weeks feeding showed that the basal diet supplemented with COSincreased the specific growth rate of sea cucumber, but no significant difference wasobserved between the treatments and the control(P>0.05). The activity of coelomocytephagocytosis of sea cucumber was not significantly influenced by dietary COS(P>0.05). However, respiratory burst activity of sea cucumbers fed the diets with COSwas significantly (P<0.05) higher than that of sea cucumbers fed the basal diet. Theactivity of nitric oxide synthase of coelomocytes was significantly higher in animals fedthe diet with0.50%chitosan COS (P<0.05); while the activity of acid phosphatase was decreased. It was significantly lower in sea cucumbers fed the diet with0.50%COScompared to the control group (P<0.05). The sea cucumber challenged with V.splendidus showed that dietary COS conferred better protection to sea cucumber, but nosignificant difference was observed compared to control group (P>0.05). These resultssuggested further studies on application of COS in sea cucumber are necessary.2.An8weeks feeding trial was conducted to determine the effect of mixed nitraterare earth (RE(NO3)3) on the growth, immune response and resistance of sea cucumberagainst Vibrio splendidus infection. The basal diet was supplemented with0,50,100,150,200and300mg/kg RE(NO3)3to formulate six experimental diets. After the feeding trial,a V. splendidus injection challenge was executed to test the effect of RE(NO3)3. Theresults of present study showed that, the basal diet supplemented with RE(NO3)3significantly increased the specific growth rate of sea cucumber compered to the controlgroup (P<0.05).The activity of coelomocyte phagocytosis and respiratory burst activityin animals fed the diet with150mg/kg RE(NO3)3was significantly (P<0.05) higherthan those of sea cucumbers fed the basal diet. The activity of acid phosphatase ofcoelomocytes was significantly higher in animals fed the diet with150mg/kg RE(NO3)3(P<0.05). While the dietary RE(NO3)3had no significant effect on superoxidedismutase activity (P>0.05). The sea cucumber was challenged with V. splendidusshowed that dietary RE(NO3)3conferred better protection to sea cucumber andsignificantly difference was observed compared to control group (P<0.05). Theseresults suggested that dietary RE(NO3)3has potential to enhance growth, immuneresponse and disease resistance of sea cucumber.3. An8week feeding trial was conducted to determine the effect of dietarysupplementation of rare earth nitrate complex with chitosan oligosaccharide（COS-Ree）on the growth, immune response and resistance of sea cucumber against Vibriosplendidus infection.The basal diet was supplemented with0,150,300,600and1200mg/kg COS-Ree to formulate five experimental diets. After the feeding trial, a V.splendidus injection challenge was executed to test the effect of COS-Ree. The resultsof feeding showed that the basal diet supplemented with300、600mg/kg COS-Reeincreased the specific growth rate of sea cucumber, but no significant difference was observed between the control, however, the specific growth rate of sea cucumber wassignificantly decreased in sea cucumbers fed diet with1200mg/kg COS-Ree (P<0.05).The coelomocyte phagocytosis activity and the acid phosphatase activity of seacucumbers fed COS-Ree at300mg/kg was significantly higher than those of seacucumbers fed the basal diet(P<0.05). However, respiratory burst of sea cucumbercoelomocytes was not significantly influenced by dietary300mg/kg COS-Ree (P>0.05).The nitric oxide synthase activity of coelomocytes was significantly increased inanimals fed the diet with600mg/kg COS-Ree (P<0.05). The acid phosphatase activitywas significantly decreased in sea cucumbers fed diets with1200mg/kg COS-Ree, butthe coelomocyte phagocytosis activity and respiratory burst of sea cucumbercoelomocytes was significantly higher compared to animals fed other experiment dietsand control diet (P<0.05). The challenge test showed that dietary300、600mg/kgCOS-Ree led to significant protection to sea cucumber against V. splendidusinfection(P<0.05), but the cumulative mortality increased in sea cucumbers fed diets with1200mg/kg COS-Ree (P<0.05). It is concluded that dietary COS-Ree has a potential ofenhancing the growth and disease resistance of sea cucumber.