Effect Of Dietary Cholesterol,soybean Lecithin And Their Interaction On The Anti-stress Ability Of Litopenaeus Vannamei In Freshwater Aquaculture

Our previous study had obtained the demand for cholesterol and soybean lecithin by the influence of cholesterol and soybean lecithin on growth,resistance to Vibrio and nitrite nitrogen stress of Litopenaeus vannamei.Based on this study,this experiment continues to explore the effects of dietary cholesterol and soybean lecithin supplementions on the immune related genes,resistance to actue low temperature and hypoxia stress,and the interaction of cholesterol and soybean lecithin on L.vannamei.A 8 weeks feeding trial was carried out to investigate the effects of dietary cholesterol(CH)content on the immunity and antistress ability in white shrimp Litopenaeus vannamei cultured in freshwater.Five isonitrogenous and isoenergetic experimental diets(CH0,CH1,CH2,CH3,CH4)were prepared to fed shrimps with initial average of(0.14±0.03)g and the measured CH content of experimental diets was0.54,1.51,2.54,3.04 and 4.14 mg/g diet,respectively.Then immune related genes expression before and after acute Vibrio parahaemolyticus infection,and the resistance to actue low temperature and hypoxia stress,are detected.The results indicated that the Toll receptor mRNA expression of CH2 group in shrimp was significantly higher than the other groups(P < 0.05),but there was no significant difference between the CH2 group and CH3 group(P > 0.05).IMD mRNA expression of CH3 group was not significantly different from CH4 group(P < 0.05),but significantly higher than that other groups(P < 0.05).While the expression of lysozyme mRNA in shrimp tissues increased with the increase of dietary CH content(P > 0.05).The supplementation of dietary CH significantly affected the expression of Toll receptor mRNA,IMD mRNA and lysozyme mRNA in shrimp after V.parahaemolyticus challenge.The peak values of Toll receptor mRNA and lysozyme mRNA expression were highest in CH2 group after infection(P < 0.05).While the peak value of IMD mRNA expression was the highest in CH1 group.Within 48 h after Vibrio infection,Toll receptor and lysozyme mRNA expression were the largest changed in CH2 group,while IMD mRNA expression changed the most in CH1 group,followed by CH2 group.In addition,Toll receptor gene expression in most groups were basically restored to the initial value,but IMD gene was not recover to the initial value in each group.There was no significant difference inoxygen consumption and lethal dissolved oxygen concentration of L.vannamei under actue hypoxia stress(P > 0.05).The mortality of each group in shrimps was insignificantly impacted under actue low temperature stress(P > 0.05).However the survival time between CH3 and CH4 groups were significantly higher than that of other groups(P < 0.05).In order to assess the effect of dietary soybean lecithin(SL)supplementation on the immunity and antistress ability in white shrimp Litopenaeus vannamei cultured in freshwater.Five isonitrogenous and isoenergetic experimental diets based on 10% fish meal formula,supplemented 0(SL0),1%(SL1),2%(SL2),3%(SL3)and 4%(SL4)dietary SL respectively,were fed to the juvenile shrimp(initial body weight 0.14±0.03 g for eight weeks.Then the resistance to actue low temperature and hypoxia stress,and immune related genes expression before and after acute infection of V.parahaemolyticus,are detected.The results indicated that the PC content of SL0,SL1,SL2,SL3 and SL4 were 1.87,2.61,3.45,4.20 and 5.41 mg/g.The Toll receptor mRNA expression in SL2 group was significantly higher than that of other groups(P < 0.05),while the expression of IMD mRNA was highest in SL3 group(P < 0.05).Besides the expression of lysozyme mRNA in shrimp tissues increased first and then decreased with the increase of SL content(P > 0.05).After acute infection of V.parahaemolyticus,dietary SL content affect the expression of Toll receptor,IMD and lysozyme mRNA in each groups.The peak values of Toll receptor mRNA,IMD mRNA and most groups lysozyme mRNA appeared in 24 h,while the peak value of lysozyme mRNA expression in SL1 group appeared at 42 h after acute infection.The peak values of Toll receptor,IMD and lysozyme mRNA expression in SL2 group were significantly higher than that in SL0 group(P < 0.05).In addition,the relative expression of Toll receptor,IMD and lysozyme mRNA in SL2 group was the largest rangeability after acute infection.Under actue hypoxia stress,there was no significant difference in oxygen consumption and lethal dissolved oxygen concentration between the shrimps of each group(P > 0.05).The death diachronic in SL3 group was higher than that of SL0 group(P < 0.05),and which was no sigificantly difference in other groups under actue low temperature stress(P > 0.05).The mortality of SL2 group was lower than that of SL1 group(P < 0.05)and no significant difference from other groups at 18 °C(P > 0.05).While the mortality was no significantly difference bewteen SL4 group and SL2 group(P > 0.05),but they were all lower than those of SL1 group at 17 °C(P < 0.05).On this basis,the effects of CH and SL supplementations on the growth,biochemical composition,immunity and anti-stress ability of L.vannamei were studied.In the present study,nine groups of isonitrogenous and isoenergetic low fishmeal dietsfor L.vannamei juveniles were formulated with three levels of CH(0,0.2,0.4%)and SL(0,2,4%)supplementations,respectively.After 8-week feeding trial,the growth performance,proximate composition of muscle,PC content,cholesterol content,digestive enzymes in hepatopancreas,immune enzyme in serum,immune-related genes(Toll receptor mRNA,IMD mRNA,lysozyme mRNA)expression prior and post experienced Vibrio alginolyticus challenge,survival after V.alginolyticus and acute nitrite challenged,lethal concentration of DO under hypoxia stress were investigated.The results showed that:1.FBW and SGR were significantly improved by increasing dietary CH supplementation(P < 0.05),while SR and FCR was insignificantly impacted(P > 0.05).There was no significant effect of dietary SL level on shrimp growth performance(P >0.05).No significant interaction between CH and SL on shrimp growth performance was detected(P > 0.05).However,the best growth performance recorded was with those fed the combination of 0.4% CH and 2% SL.Total lipids and cholesterol levels in muscle,hepatopancreas and serum increased with increasing dietary CH(P < 0.05),whereas a decrease in PC and cholesterol in muscle,and serum was obtained when dietary SL was administered at increasing levels(P < 0.05).Although,a synergistic effect was observed between CH and SL on levels of crude protein,PC and cholesterol in muscle,hepatopancreas and the serum(P < 0.05).Protease activity in the hepatopancreas was the lowest at 0.2% CH level(P < 0.05).CH levels were found to positively correlate with amylase activity(P < 0.05),and negatively correlate with lipase activity(P < 0.05).The activity of protease and lipase increased initially and then decreased with increasing SL levels(P < 0.05).The significant effects were observed between CH and SL on digestive enzyme activity of hepatopancreas in L.vannamei(P< 0.05).Toll receptor mRNA,lyszomye mRNA and IMD mRNA expression in gill tissue of shrimp were not significantly impacted by dietary CH(P > 0.05).However,with increasing dietary SL,expression of IMD mRNA and Toll receptor mRNA increased,albeit not to a significant level(P > 0.05).Similarly,lysozyme mRNA expression trended towards up-regulation after an initial decrease in expression(P <0.05).There was a significant interaction between CH and SL on the Toll receptor mRNA and lysozyme mRNA(P < 0.05),but not IMD mRNA(P > 0.05).2.The results indicated that lysozyme activity rose and SOD activity declined initially then increased significantly with the increasing levels of CH(P < 0.05).When dietary SL increased,the activity of SOD rose significantly(P < 0.05),but not the lysozyme(P > 0.05).The interaction between CH and SL had an obvious impact on the activity of SOD(P < 0.05),but not the lysozyme either(P > 0.05).The supplementationof dietary CH and SL significantly affected the relative expression of Toll receptor mRNA,IMD mRNA and lysozyme mRNA in shrimp after V.alginolyticus challenge.With the increasing levels of CH,the peak values of Toll receptor mRNA,IMD mRNA and lysozyme mRNA expression were improved,along with the delayed peak for Toll receptor mRNA expression and advanced peak for IMD mRNA and lysozyme mRNA expression.By the increasing levels of SL,the peak values of Toll receptor mRNA expression increased initially and then decreased,but improved for IMD mRNA and lysozyme mRNA.The peak time of the Toll receptor mRNA expression appeared in advance,while the peak time of the lysozyme mRNA expression was delayed with increasing dietary SL.The 0.4% CH-4% SL treatment showed the lowest cumulative mortality within 96 h when the shrimp experienced Vibrio challenge(P < 0.05).The cumulative mortality of 96 h in the 0.2% CH-2% SL group was the lowest after nitrite nitrogen stress(P < 0.05).There was no significant interaction between CH and SL on the lethal concentration of DO(P > 0.05).The lethal dissolved oxygen concentration were negatively correlated with CH levels(P < 0.05),while SL levels had no significant effect on the lethal dissolved oxygen concentration(P > 0.05).The 0.4% CH-2% SL treatment showed the lowest of l lethal dissolved oxygen concentration.