| The turbot, Scophthalmus maximus L., has been recognized by Chineseconsumers as one of the most valued mariculture fishes. However, disease threats andantibiotic abuse affect the production of turbot. The purpose of the present work isconducted to investigate the immunoenhancement effect of dietary rare earth elements（REE） and its complex with chitosan oligosaccharideare （COS-REE）, and we usecerium （Ce） as the representative elements to investigate the alleviation effects ofelevated dietary Ce and its complex with chitosan oligosaccharide （COS-Ce） oncadmium （Cd） accumulation in juvenile turbot. The results are as follows.1. An8-week-feeding trial was conducted to investigate the effect of dietaryCOS-REE on growth performance and innate immune response of turbot as well asdisease resistance against Edwardsiella tarda. The basal diet was formulated using fishmeal as protein sources, fish oil and soybean lecithin as lipid sources and wheat meal assugar source. Five practical diets were formulated to contain graded levels (75,150,300,600and1200mg kg-1) of COS-REE. Fish of the same size （initial average weigh of（12.16±0.01） g） were randomly distributed into18300L cylindrical fiberglass tanks in acirculating water system. Each diet was randomly assigned to triplicate tanks. Each tankwas stocked with40fish, and fish in each tank received a specific different diet twice aday （07:00and18:00）. During the experimental period, the water temperature fluctuatedfrom19to20°C, pH from7.5to7.8and salinity from24‰to27‰. Air stones in eachtank maintained the dissolved oxygen concentration at7mg L-1or more. Results of thepresent study showed that, compared to the control group, the specific growth rate （SGR）was significantly higher in fish fed the diet with300mg kg-1COS-REE （P <0.05）,whereas the phagocytic index （PI） and the activity of super oxide dismutase（SOD） ofserum was significantly higher than those in fish fed the control diet （P <0.05）. After8weeks, fish were challenged by intraperitoneal injection with E. tarda for7days, COS-REE-treated fish demonstrated increased protection capability. These resultssuggested that COS-REE could enhance growth, innate immunity and disease resistancein turbot, and the optimum dose was approximately300mg kg-1.2. The present study was conducted to investigate the effects of dietary REE ongrowth and innate immune response of turbot （initial average weight of （12.88±0.15） g）.Four practical diets were formulated to contain graded levels (50,100,150and200mg kg-1) of REE. The results of8weeks feeding trial showed that the basal dietsupplemented with100mg kg-1REE increased the survival rate by10.33%, SGR washigher than the control group. Furthermore, the activity of lysozyme （LZM） of serium infish fed the diet with REE was higher than those fed with the control diet. Theconcentrations of hepatic metallothionein （MT） in fish fed the diet with200mg kg-1REEwere significantly higher than the control group. These results suggested that REE couldbe used in turbot culture as an immunostimulant.3. An8weeks feeding trial was conducted to investigate the alleviation effect ofdietary COS-Ce on Cd accumulation of turbot under Cd stress in a room flowingwater system. The basal diet were added different doses of CdCl22H2O and COS-Ce.The turbot （initial average weight of （12.76±0.17） g） were randomly divided into thecontrol group, the50mg kg-1Cd2+)exposed group and the low (50mg kg-1Cd2++50mg kg-1COS-Ce), moderate (50mg kg-1Cd2++100mg kg-1COS-Ce), high (50mg kg-1Cd2+)+200mg kg-1COS-Ce) intervention group. Results of the present study showedthat, compared to the control group, the condition factors significantly decreased inCd-exposed group, whereas the cadmium concentration in liver, kidney and fencesignificantly increased （P <0.05） and the hepatic MT concentrations were2.1-fold.Compared to the Cd-exposed group, the survival rate was higher and conditionfactors were significantly higher （P <0.05） in the high intervention group, Cdconcentration decreased by51.72%. In the moderate intervention group, the cadmiumconcentration decreased28.31%、26.73%、25.86%、21.88%and11.43%in the kidney,liver, muscle, gill and bone, respectively. The activity of hepatic glutathioneperoxidase （GSH-PX） significantly increased than the Cd-exposed group. Theseresults suggested that elevated COS-Ce could protect against dietary Cd uptake and enhance antioxidase activity in liver.4. The objective of this study was to examine the alleviation effect of dietary Ceon Cd accumulation of turbot under Cd stress. The basal diet were added differentdoses of CdCl22H2O and CeCl37H2O. The turbot （initial average weight of（12.79±0.08） g） were randomly divided into the control group, the50mg kg-1Cd2+exposed group and the low (50mg kg-1Cd2++50mg kg-1Ce3+), moderate (50mgkg-1Cd2++100mg kg-1Ce3+), high (50mg kg-1Cd2++200mg kg-1Ce3+) interventiongroup. Results of8weeks feeding trial showed that, compared to the Cd-exposedgroup, the condition factors and survival rate increased in the lower interventiongroup and the Cd concentration of muscle, liver, kidney and gill decreased22.41%、22.40%、18.82%and9.38%, respectively. The activity of hepatic GSH-PXsignificantly increased than the Cd-exposed group. These results suggested thatelevated Ce3+could protect against dietary Cd uptake and enhance antioxidase activityin liver. |
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