| Chinese shrimp?Fenneropenaeus chinensis?is a unique species in China's coastal waters.It mainly distributes in the Yellow Sea,Bohai Sea and the western coast of North Korea.It is the main species of marine aquaculture in China.In recent years,high-density culture has become an important way to increase the production of shrimp culture and reduce the cost of shrimp culture.However,with the continuous expansion and over-intensive aquaculture,the competition of resources and space among individuals will lead to a series of changes in animal growth,energy physiology and immune function,which may ultimately lead to the decline of animal viability and affect the growth and immunity of shrimp.In this paper,the suitable density of different stages of F.chinensis was studied.The neuroendocrine regulation mechanism of F.chinensis under density stress,the metabolic pathways,energy distribution patterns,immune changes and the effects of feed additives on F.chinensis under density stress were investigated,which laid a theoretical foundation for further understanding of the tolerance mechanism of F.chinensis to density.It has strong theoretical research value and practical guiding significance.The research results are as follows:1.Effect of density stress on growth,antioxidant system function and water quality index of juvenile F.chinensisThis study analysed the effection growth,non-specific immune function and water quality of juvenile shrimps F.chinensis in four socking of density for G0?250ind/m3?,G1?500 ind/m3?,G2?1000ind/m3?,G3?2000 ind/m3?by 40-day indoor culture experiment.The results showed that the survival rate and growth index of G1 and G2 were not significant with G0?P>0.05?,G3 was significantly lower than G0 at20 days?P<0.05?.G1 and G2 were significantly lower than G0?P<0.05?and G3 and G0 is extremely significant?P<0.01?at 40 days.By measuring the antioxidant status in serum,hepatopancreas,gill and muscle tissue,the antioxidant parameters showed:Total antioxidative capacity?T-AOC?,superoxide dismutase?SOD?,hydrogen peroxide?CAT?and glutathione peroxidase?GPx?increased first and then decreased with the increase of density.At 20 days,the G1 and G2 in four oxidation indexes were significantly higher than G0?P<0.05?and were significantly lower than G0?P<0.05?at 40 days.The content of malondialdehyde?MDA?increased gradually with the increase of density:the MDA of G3 was always significantly higher than G0?P<0.05?.The MDA of G1 and G2 significantly higher than G0 in hepatopancreatic tissue at 40d?P<0.05?,the other tissues were not significant?P>0.05?.The pH,DO,NO2-N,NO3-N,NH3-N and COD had no significant effect on the main water quality indexes?P>0.05?in different densities,which were all within the suitable range for the growth of F.chinensis.The results showed that density stress significantly affects the growth and antioxidant capacity of F.chinensis with a suitable density of 1000/m3 for20 days and a suitable density of 250/m3 for 40 days.2.Effect of density stress on muscle stress protein and biogenic amines in F.chinensisThis study analysed the effection muscle stress protein content and gene expression of F.chinensis in four socking of density for P1?100ind/m3?,P2?200 ind/m3?,P3?300 ind/m3?,P4?400 ind/m3?by 7-day indoor culture experiment.The results showed that the protein content of actin T2,14-3-3-like protein and pyruvate kinase 3 in F.chinensis increased first and then decreased after density stress,and the higher the density,the higher the content.The contents of actin T2 in P2,P3 and P4reached the maximum at 1d,0.5d and 0.5d,respectively,and were significantly different from P1 in each time period?P<0.05?.P3 and P4pyruvate kinase 3 levels were significantly higher than those in P1 and P4.P1?P<0.05?reached the maximum at 1d,and P2 and P1 was not significant?P>0.05?.The 14-3-3 protein content of P2,P3 and P4reached the maximum at 1d.P2 and P3 significantly higher than P1?P<0.05?,the P4 and P1 was extremely significant?P<0.01?.At the end of the experiment,only P4 content was significantly higher than P1?P<0.05?.The expression of 14-3-3 protein and pyruvate kinase 3 gene was up-regulated in quantitative RT-PCR,protein level and gene level were positively correlated;actin T2 gene expression was down-regulated,protein level and gene level were negatively correlated,Changes in three protein may result in decreased muscle mass of shrimp after density stress.Determination of hemolymph dopamine?DA?,norepinephrine?NE?,and serotonin?5-HT?levels in F.chinensis by P4?400 tails/m3?and de-eye group?400 tails/m3?.The effects of amines and the regulation of CHH on biogenic amines showed that the contents of three kinds of biogenic amines changed significantly under density stress,and the contents of DA,NE and 5-HT in P2,P3 and P4 density groups increased first and then decreased,the maximum value was obtained at 1d,3d,and5d,which was significantly higher than P1?P<0.05?.After that,the all decreased to the level of the control group,and the difference was not significant?P>0.05?.After removing the eyestalk,the DA content decreased significantly at 12h and 1d,the NE content decreased significantly at 1d and 3d,the 5-HT content decreased significantly at 3d and 5d,and the three organisms all responded at density stress.But the responded time from long to short is respectively was DA,NE and 5-HT.This indicates that CHH can regulate the content of biogenic amines,but the effect of CHH on the content of three biogenic amines is different.3.Effects of density stress on growth,metabolites and metabolic enzymes in F.chinensisThe effects of F.chinensis on growth indices,metabolic substance content and metabolic enzyme activity at four culture densities?P1?100tails/m3?,P2?200 tails/m3?,P3?300 tails/m3?,P4?400 tails/m3??were studied in a 28-day indoor culture experiment.The results showed that he survival rate,weight gain rate,growth rate,relative growth rate and specific growth rate of F.chinensis decreased significantly with the increase of density?P<0.05?,and the coefficient of weight difference increased significantly?P<0.05?.High density treatment could significantly increase blood sugar,lactic acid,pyruvic acid and triglyceride content in haemolymph,but had little effect on amino acids.This indicated that under density stress,F.chinensis tended to use carbohydrates and lipids as energy sources,indicating that high density stress could increase the utilization of carbohydrates and lipids.Because of the increasing demand for energy,the utilization of metabolic substances must be improved.The activities of hexokinase,pyruvate kinase,fructose-6-phosphate kinase and lactate dehydrogenase increased significantly under density stress.This indicates that the oxidative metabolic pathway changes,catabolism increases,aerobic metabolism is inhibited,and anaerobic metabolism is activated at the same time.4.Effects of feed additives on growth and immune index of F.chinensis under density stressThe effects of dietary vitamin C and oligosaccharides on the growth,immunity and digestive enzymes of F.chinensis were studied under the stress of 400 tails/m3 in a 28-day indoor culture experiment.The experiment was divided into four groups:C0?formula feed?,C1?adding0.1%Vc?,C2?adding 0.16%oligosaccharide?,C3?mixing group,1/2 of adding C1 and C2?.The results showed that under density stress,the effect of feed additives on the growth of F.chinensis was significant,the order was C3>C1>C2,and the effect of mixed group was the most obvious.The weight gain rate,growth rate,relative growth rate and specific growth rate of C1 and C3 were significantly higher than those of the control group?P<0.05?.The growth indexes of C2 group were higher than those of the control group,with only significant difference in growth rate?P<0.05?,while other differences were not significant?P>0.05?.The effects of feed additives on immune indexes under density stress:the immune indexes of C1,C2 and C3 groups were higher than those of C0groups,and the activity of AKP reached the maximum at 7 days,but the difference was not significant?P>0.05?.The activities of PO,SOD,ACP and lysozyme in C1 and C3 groups were significantly increased?P<0.05?.The activities of immune enzymes in C3 group were higher than those in C1 group.The activities of PO,ACP and lysozyme in C2 group were significantly higher than C0?P<0.05?.The effects of feed additives on digestive enzymes under density stress:The activities of digestive enzymes in C1,C2 and C3 groups increased at 1 day,and played the greatest role at 7 days,the activity was higher than that of the control group.The activities of protease,amylase and trypsinase of shrimp were significantly increased in C1 and C3 groups?P<0.05?.C2 group significantly increased protease and trypsin?P<0.05?,but had no significant effect on amylase?P>0.05?.In conclusion,adding vitamin C and oligosaccharides to the feed can improve the growth,immunity and digestive enzymes activities of F.chinensis,feeding additives can alleviate the impact of density stress,but can not eliminate it,and the effect of combined addition is the best. |
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