| This experiment took Micropterus salmoides as the experimental object and added 100mg/kg silymarin to the feed of Micropterus salmoides.By utilizing 5 different feeding strategies(Group 1(0/0): control group;Group 2(0/4): subsequent 4-week alternating feeding group;Group 3(0/2): 2-week alternating feeding group;Group 4(4/0): previous 4-week alternating feeding group;The fifth group(4/4): 8-week continuous feeding group)conducted an 8-week aquaculture cycle on Micropterus salmoides.Through the following four parts:(1)The effects of different feeding strategies of silymarin on the growth performance and body composition of Micropterus salmoides(growth performance,feed utilization,body indicators and nutritional composition indicators);(2)Effects of different feeding strategies of silymarin on antioxidant capacity of Micropterus salmoides(serum antioxidant enzyme and antioxidant-related gene expression and other indicators);(3)Effects of different feeding strategies of silymarin on immunity of Micropterus salmoides(plasma routine indexes,plasma non-specific immune indexes,immune-related gene expression and disease resistance);(4)The effects of different feeding strategies of silymarin on fat metabolism of Micropterus salmoides(fat metabolism enzyme and lipid metabolism-related gene expression and other indicators),to study the effects of different feeding strategies of silymarin in feed on the growth,antioxidant,immunity and lipid metabolism of Micropterus salmoides and the optimal feeding strategy of silymarin in the culture process of Micropterus salmoides,aiming to provide a reference for the development and reasonable application of functional feed additives and the healthy aquaculture development of fish.The main research results are as follows:(1)Effects of different feeding strategies of silymarin on growth performance and body composition of Micropterus salmoidesDifferent feeding strategies of silymarin had significant effects on the growth performance,feed utilization,nutritional composition and body indicators of Micropterus salmoides(P<0.05).The survival rate(SR)of groups 2,3,4 and 5 was significantly higher than that of the control group(P<0.05)and the final average weight(FBM),the weight gain rate(WGR)and specific growth rate(SGR)of group 3 were significantly higher than the other groups(P<0.05),the Feed efficiency rate(FER)of group 3 was significantly higher than that of the other groups(P<0.05),and the protein efficiency rate(PER)of groups 2 and 3 was not significantly different from that of group 5(P>0.05),but significantly higher than that of other groups(P<0.05).The crude protein(CP)and crude ash content in group 5 were significantly higher than those in the control group(P<0.05),but there was no significant difference with the other groups(P>0.05),and crude fat(EE)in group 5 was not significantly different from group 2 and group 3(P>0.05),but all three were significantly lower than those in the control group(P<0.05).There were no significant differences between the Invasive pulmonary fungal infections(IPFI),Viscero somatic index(VSI),and hepato somatic index(HSI)in groups 2 and 3 and group 5(P>0.05),but both were significantly lower than those in the control group(P<0.05).Based on the above results,it shows that the 2-week alternating feeding strategy of silymarin has a better effect on the growth,feed utilization,nutritional composition and body indicators improvement of Micropterus salmoides,which has certain guiding significance in production.(2)Effects of different feeding strategies of silymarin on antioxidant capacity of Micropterus salmoidesDifferent feeding strategies of silymarin had significant effects on serum antioxidant enzyme activity and tissue antioxidant gene expression in Micropterus salmoides(P<0.05).The activity of malondialdehyde(MDA)in group 5 was significantly lower than that of other groups(P<0.05),there was no significant difference between MDA in group 2 and group 3(P>0.05),but significantly lower than that of group 4 and control group(P<0.05),the activity of glutathione peroxidase(GSH-Px)in group 2 was significantly higher than that of other groups(P<0.05),and the activity of catalase(CAT)in group 2 was not significantly different from that of group 3 and group 5(P>0.05),but significantly higher than that of control group and group 4(P<0.05);group 2 There was no significant difference in total antioxidant capacity(T-AOC)between groups 3 and 5 and group 4(P>0.05),but all three were significantly higher than those in the control group(P<0.05).CAT,GPX1α and SOD1 genes were expressed in liver,intestine and muscle tissues,but silymarin had no significant effect on the expression of CAT,GPX1αand SOD1 genes in muscle tissues(P>0.05),and in liver and intestinal tissues,the expression of CAT,GPX1α and SOD1 genes in group 2 was not significantly different from that in group 3and group 5(P>0.05),but all were significantly higher than those in the control group(P<0.05).Based on the above results,it is found that the subsequent 4-week alternating feeding strategy has a better effect on improving the antioxidant capacity of Micropterus salmoides in other silymarin feeding strategies.(3)Effects of different feeding strategies of silymarin on the immunity of Micropterus salmoidesDifferent feeding strategies of silymarin had significant effects on the total number of plasma immune cells,non-specific immune indexes,expression of inflammation-related genes and disease resistance in Micropterus salmoides(P<0.05).The total number of red blood cells and lymphocytes in group 2,group 3 and group 5 were significantly higher than those in the control group and group 4(P<0.05),and the total number of white blood cells between group 2and group 3 was not significantly different(P>0.05),but it was significantly lower than that in other groups(P<0.05).The activities of superoxide dismutase(SOD)and alkaline phosphatase(AKP)in groups 2 and 3 were not significantly different from those in group 5(P>0.05),but significantly higher than those in control and group 4(P<0.05),and lysozyme(LZM)in groups2,3 and 5 was not significantly different from group 4(P>0.05),but significantly higher than that in control(P<0.05).Tumor necrosis factor-alpha(TNFα),Transforming growth factor-β1(TGF-β1),Interleukin-1β(IL-1β)and Interleukin-10(IL-10)genes were expressed in liver,intestine and muscle tissues,but different feeding strategies of silymarin had no significant effect on the expression of TNFα,IL-1β and IL-10 genes in muscle tissues(P>0.05),while Group 2,There was no significant difference in TGF-β1 gene expression in groups 3 and 5(P>0.05)from group 4,but significantly higher than in the control group(P<0.05);in liver and intestinal tissue,TGF-β1 and IL-10 gene expression in group 3 was not significantly different from that in group 2 and group 5(P>0.05),but significantly higher than that in group 4 and control(P<0.05),and the expression of TNFα,and IL-10 genes in group 3 was not significantly different from that in group 2 and group 5(P>0.05),but significantly higher than that in group4 and control(P<0.05),and the expression of TNFα,and IL-1β gene expression was not significantly different from Group 2(P>0.05),but significantly lower than that of other groups(P<0.05).There was no significant difference in survival between groups 2,3 and 5 after the challenge test,(P>0.05),but significantly higher than that between group 4 and control(P<0.05).Based on the above results,it is found that the 2-week alternating feeding strategy has a better effect on improving the immunity of Micropterus salmoides in other silymarin feeding strategies.(4)Effects of different feeding strategies of silymarin on fat metabolism in Micropterus salmoidesDifferent feeding strategies of silymarin had significant effects on the activity of fatty metabolism enzyme and the expression of Messenger RNA(m RNA)of lipid metabolism-related genes in Micropterus salmoides(P<0.05).The activities of hepatic lipase(HL)and Lipoprotein lipase(LPL)in groups 2,3 and 5 were significantly higher than those in the control group(P<0.05),while the activities of fatty acid synthase(FAS)and acetyl-Co A carboxylase(ACC)were significantly lower than those in the control group.Fatty acid synthase(FAS),stearoyl-coa desaturates(SCD),homone sensitive lipase(HSL),lipoprotein lipase(LPL)and peroxisome proliferators-activated receptor-α(PPAR-α)genes were expressed in liver,intestinal and muscle tissues,among which the FAS and SCD genes in group 2 had the lowest expression in each tissue and were significantly lower than those in the control group(P<0.05),while the HSL,LPL and PPAR-α genes in group 2 had the highest expression in each tissue and significantly higher than that in the control group(P<0.05).Based on the above results,the results show that the subsequent 4-week alternating feeding strategy has a better ability to enhance the lipid metabolism of Micropterus salmoides in other silymarin feeding strategies.The above research results indicate that the 2-week alternating feeding strategy of silymarin has a better effect on improving the growth and immunity of Micropterus salmoides among other feeding strategies;The subsequent 4-week alternating feeding strategy has a better effect on improving the body’s antioxidant capacity and lipid metabolism.Therefore,it is recommended to adopt these two silymarin feeding strategies in the breeding process of Micropterus salmoides,so as to provide a theoretical basis for reducing breeding costs,improving disease resistance of the fish,and increasing breeding benefits in production. |
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