Effects Of Dietary Immunostimulants On Growth, Non-specific Immune Response And Stress Resistance Of Juvenile Pacific White Shrimp, Litopenaeus Vannamei

A series studies were conducted to evaluate the effects of dietary immunostimulantson growth, non-specific immune response and stress resistance of juvenile Pacific whiteshrimp Litopenaeus vannamei. The results obtained can be briefly summarized asfollows:1. An8-week feeding trial and dissolved oxygen stress subsequently conducted toevaluate the effects of dietary astaxanthin (AX) on growth, non-specific immuneresponse and stress resistance of juvenile Pacific white shrimp Litopenaeus vannamei.Seven diets with or without AX supplementation namely Control (Basal feed (BF)without AX), AX25(BF+25mg AX kg-1diet), AX50(BF+50mg AX kg-1diet), AX75(BF+75mg AX kg-1diet), AX100(BF+100mg AX kg-1diet), AX125(BF+125mg AXkg-1diet) and AX150(BF+150mg AX kg-1diet) were fed to Litopenaeus vannamei (1.01±0.00g) for8weeks in35tanks (30shrimp per tank). The results showed that shrimp fedAX125and AX150diets had higher (P<0.05) weight gain (WG), specific growth rate(SGR), total antioxidant status (TAS) and lower (P<0.05) superoxide dismutase (SOD),catalase (CAT) than shrimp fed control diet. However, Aspartate aminotransferase (AST)and alanine aminotransferase (ALT) activities were not significantly different (P>0.05) between AX-supplemented groups and control group. After low dissolved oxygen stressfor1h, survival rate of shrimp fed AX75, AX100, AX125and AX150diets were higher(P<0.05) than that of shrimp fed control diet. Hypoxia-inducible factor alpha (HIF^-1α),SOD and CAT mRNA expression levels of shrimp fed seven diets were significantlydown-regulated under hypoxia than under normoxia, but their expression levels werehigher under hypoxia in shrimp fed AX-supplemented diets than in shrimp fed controldiet.70-kDa heat-shock protein (Hsp70) mRNA expression level of shrimp fed sevendiets was significantly up-regulated under hypoxia than under normoxia, but itsexpression level was lower under hypoxia in shrimp fed AX-supplemented diets than inshrimp fed control diet. These results indicated that125mg kg^-1and150mg kg^-1AX-supplementation could improve growth, non-specific immune response andammonia stress resistance in juvenile L. vannamei.2. An8-week feeding trial and ammonia stress subsequently conducted to evaluatethe effects of dietary chitosan (CHS) on growth, non-specific immune response and stressresistance of juvenile Pacific white shrimp Litopenaeus vannamei. Seven diets with orwithout CHS supplementation namely Control (Basal feed (BF) without CHS), CHS1.0(BF+1.0g CHS kg^-1diet), CHS2.0(BF+2.0g CHS kg^-1diet), CHS3.0(BF+3.0g CHSkg^-1diet), CHS4.0(BF+4.0g CHS kg^-1diet), CHS5.0(BF+5.0g CHS kg^-1diet) andCHS6.0(BF+6.0g CHS kg^-1diet) were fed to Litopenaeus vannamei (0.71±0.00g) for8weeks in35tanks (30shrimp per tank). The results showed that shrimp fed allexperimental diets had no significant difference (P>0.05) on growth performance.However, shrimp fed CHS3.0diet had higher (P<0.05) phenoloxidase (PO) andlysozyme (LSZ) activities than shrimp fed control diet. After120mg L^-1ammonia stressfor72h, survival rate of shrimp fed CHS1.0, CHS3.0, CHS4.0, CHS5.0and CHS6.0diets were significantly higher (P<0.05) than that of shrimp fed control diet. These resultsindicated that although CHS-supplementation could not improve growth performance,3.0g kg^-1CHS-supplementation could enhance non-specific immune response andammonia stress resistance in juvenile L. vannamei.3. An8-week feeding trial and ammonia stress subsequently conducted to evaluatethe effects of dietary fructooligosaccharides (FOS) on growth, non-specific immune response and stress resistance of juvenile Pacific white shrimp Litopenaeus vannamei.Six diets with or without FOS supplementation namely Control (Basal feed (BF) withoutFOS), FOS0.5(BF+0.5g FOS kg^-1diet), FOS1.0(BF+1.0g FOS kg^-1diet), FOS1.5(BF+1.5g FOS kg^-1diet), FOS2.0(BF+2.0g FOS kg^-1diet) and FOS2.5(BF+2.5g FOSkg^-1diet) were fed to Litopenaeus vannamei (0.60±0.00g) for8weeks in24tanks (30shrimp per tank).The results showed that shrimp fed FOS0.5and FOS1.0diets had higher(P<0.05) WG, SGR, and lower (P<0.05) feed conversion ratio (FCR) than shrimp fedcontrol diet. Shrimp fed FOS2.0had lower (P<0.05) survival rate than shrimp fed controldiet. PO and alkaline phosphatase (AKP) activities of1.0g kg^-1FOS-supplementedgroup were significantly higher (P<0.05) than that of control group. Acid phosphatase(ACP) activity of1.0,1.5,2.0and2.5g kg^-1FOS-supplemented groups was significantlyhigher (P<0.05) than that of control group. After120mg L^-1ammonia stress for60h, allFOS-supplemented groups had significantly higher (P<0.05) survival rate than controlgroup. These results indicated that1.0g kg^-1FOS-supplementation could improve growth,non-specific immune response and ammonia stress resistance in juvenile L. vannamei.4. An8-week feeding trial and ammonia stress subsequently conducted to evaluatethe effects of dietary mannan oligosaccharide (MOS) on growth, gut morphology,non-specific immune response and stress resistance of juvenile Pacific white shrimpLitopenaeus vannamei. Six diets with or without MOS supplementation namely Control(Basal feed (BF) without MOS), MOS12(BF+0.12g MOS kg^-1diet), MOS24(BF+0.24g MOS kg^-1diet), MOS48(BF+0.48g MOS kg^-1diet), MOS72(BF+0.72g MOS kg^-1diet) and MOS96(BF+0.96g MOS kg^-1diet) were fed to Litopenaeus vannamei (2.52±0.01g) for8weeks in36cement tanks (30shrimp per tank).The results showed thatshrimp fed0.24,0.48,0.72and0.96g kg^-1MOS-supplemented diets had significantlyhigher (P<0.05) WG and SGR than shrimp fed control diet. Compared with control group,SEM and TEM analysis revealed that MOS-supplementation could significantly increase(P<0.05) the intestinal microvilli density and length of shrimp at the untrastructural level.After160mg L^-1ammonia stress for24h, survival rate of shrimp fed0.24,0.48,0.72and0.96g kg^-1MOS-supplemented diets was significantly higher (P<0.05) than that ofshrimp fed control diet. PO activity of0.48g kg^-1MOS-supplemented group was significantly higher (P<0.05) than that of control group under normal conditions, and POactivity significantly decreased (P<0.05) under ammonia stress than under normalconditions, but PO activity of0.48g kg^-1MOS-supplemented group was alsosignificantly higher (P<0.05) than that of control group under ammonia stress. SODactivity of0.48,0.72and0.96g kg^-1MOS-supplemented groups was significantly higher(P<0.05) than that of control group under normal conditions. These results indicated thatMOS supplementation could improve growth, gut morphology, non-specific immuneresponse and ammonia stress resistance in L. vannamei, and the0.24-0.48g kg^-1MOSsupplementation was suitable for L. vannamei.5. An8-week feeding trial and ammonia stress subsequently conducted to evaluatethe effects of dietary β-glucan on growth, non-specific immune response and stressresistance of juvenile Pacific white shrimp Litopenaeus vannamei. Seven diets withdifferent glucan-supplemental levels and feeding strategies namely Control (feedingβ-glucan-free diet continuously), Treatment1(feeding dietary0.3g kg^-1β-glucancontinuously), Treatment2(feeding dietary0.6g kg^-1β-glucan continuously), Treatment3(feeding dietary0.9g kg^-1β-glucan continuously), Treatment4(feeding dietary0.3g kg^-1β-glucan discontinuously), Treatment5(feeding dietary0.6g kg^-1β-glucandiscontinuously) and Treatment6(feeding dietary0.9g kg^-1β-glucan discontinuously)were fed to Litopenaeus vannamei (1.00±0.00g) for8weeks in35tanks (30shrimp pertank). The results showed that shrimp fed Treatment4, Treatment5and Treatment6dietshad higher (P<0.05) WG and SGR than shrimp fed control diet. PO, SOD, LSZ andLipopolysaccharide and β^-1,3-glucan binding protein (LGBP) mRNAs expression levelin hepatopancreas of Litopenaeus vannamei fed with all experimental diets wereexamined by real-time quantitative RT-PCR. PO mRNA expression level of shrimp fedTreatment5and Treatment6diets was significantly higher (P<0.05) than control diet.SOD mRNA expression level of shrimp fed all β-glucan diets was significantly higher(P<0.05) than control diet. There was no significant difference (P>0.05) of LSZ mRNAexpression level between β-glucan diets and control diet. LGBP mRNA expression levelof shrimp fed all β-glucan diets was significantly higher (P<0.05) than control diet,meanwhile, LGBP mRNA expression level of shrimp fed Treatment2, Treatment3, Treatment4, Treatment5and Treatment6was significantly higher (P<0.05) thanTreatment1. After160mg L^-1ammonia stress for24h, survival rate of shrimp fedTreatment4, Treatment5and Treatment6diets was significantly higher (P<0.05) than thatof shrimp fed control diet. PO activity of Treatment5and Treatment6was significantlyhigher (P<0.05) than that of control group under normal conditions, and PO activity ofall experimental groups significantly decreased (P<0.05) under ammonia stressconditions, but PO activity of Treatment6was also significantly higher (P<0.05) than thatof control group under ammonia stress conditions. SOD activity of Treatment5andTreatment6was significantly lower (P<0.05) than that of control group under normalconditions, and SOD activity of all experimental groups had no significant change(P>0.05) under ammonia stress conditions. LSZ activity of all experimental groups hadno significant difference (P>0.05) under normal conditions, but LSZ activity ofTreatment4, Treatment5and Treatment6was significantly increased (P<0.05) underammonia stress conditions. Moreover, LSZ activity of Treatment2, Treatment3,Treatment4, Treatment5and Treatment6groups was significantly higher (P<0.05) thanthat of control group under ammonia stress. These results indicated that feeding dietary0.3-0.9g kg^-1glucan-supplementation discontinuously could improve growth,non-specific immune response and ammonia stress resistance in L. vannamei.6. An8-week feeding trial and low dissolved oxygen stress subsequently conductedto evaluate the effects of dietary chitosan-Zn (CHS-Zn) on growth, non-specific immuneresponse and stress resistance of juvenile Pacific white shrimp Litopenaeus vannamei.Five diets namely Control (Basal feed (BF) without CHS-Zn), CHS3000(BF+3000mgCHS kg^-1diet), CHS-Zn25(BF+25mg CHS-Zn kg^-1diet), CHS-Zn50(BF+50mgCHS-Zn kg^-1diet) and CHS-Zn100(BF+100mg CHS-Zn kg^-1diet) were fed toLitopenaeus vannamei (1.49±0.01g) for8weeks in25cement tanks (40shrimp pertank). The results showed that shrimp fed all experimental diets had no significantdifference (P>0.05) on growth performance. However, shrimp fed3000mg kg^-1CHS and100mg kg^-1CHS-Zn diets had higher (P<0.05) PO and lysozyme LSZ activities thanshrimp fed control diet. SOD activity of all experimental groups had no significantdifference (P>0.05). PO, SOD and LSZ mRNAs expression level in hepatopancreas of Litopenaeus vannamei fed with all experimental diets were examined by real-timequantitative RT-PCR. PO mRNA expression level of shrimp fed3000mg kg^-1CHS and100mg kg^-1CHS-Zn diets was significantly higher (P<0.05) than control diet. SODmRNA expression level of shrimp fed100mg kg^-1CHS-Zn diet was significantly higher(P<0.05) than control diet. LSZ mRNA expression level of shrimp fed3000mg kg^-1CHS,50mg kg^-1CHS-Zn and100mg kg^-1CHS-Zn diets was significantly higher (P<0.05)than control diet. After low dissolved oxygen stress for6h, survival rate of shrimp fedCHS-Zn100diet was significantly higher (P<0.05) than that of shrimp fed control diet.These results indicated that although CHS-Zn-supplementation could not improvegrowth performance,100mg kg^-1CHS-Zn-supplementation could enhance non-specificimmune response and low dissolve stress resistance in juvenile L. vannamei.