| Nibea albiflora belongs to Perciformes,Sciaenidae,and Nibea.It is an important marine economic fish in China.It has the characteristics of fast growth,strong resistance and strong fertility.It is launched offshore.Suitable varieties for cage culture and factory farming.N.albiflora is a variety that adapts to a wide range of salinity and belongs to the broad-sea salt marine fish.Salinity of water is a very important environmental factor for fish growth,metabolism and breeding.Salinity changes are closely related to fish health.So far,there have been many studies on the effects of salinity on fish growth,tissue antioxidant enzyme activities and non-specific immunity.On this basis,there are few studies on the effects of salinity on intestinal microbial diversity.In this paper,based on the effects of salinity on tolerance,growth,tissue antioxidant enzyme activities and non-specific immunity and metabolic parameters of squid,paraffin sections were used to study the effect of salinity on tissue structure,using 16S rDNA.Amplicon sequencing technology was used to study the changes of salinity on intestinal microbial diversity,and the effects of corresponding microorganisms on the intestinal health of N.albiflora were investigated.The aim is to provide data for the cultivation of N.albiflora in water bodies with different salinity.The study consists of three parts.1.Study on salinity tolerance of N.albiflora.This part of the experiment is divided into salinity S0(salinity 0),S2,S4,S6,S8,S40,S45,S50,S55,S60 group,a total of 10 groups,each group of 3 parallel.Two sizes of yellow croaker were used,ie size ?:average body mass was180.29±2.26 g(mean±SD),the average length was 25.7±0.51 cm;specification II:average body mass was 17.3±0.8 g,The average length is 9.52±0.7 cm.The yellow croaker was directly transferred from the natural seawater into each group and subjected to short-term salinity stress for 1 week.The results showed that the survival rate was 100%under salinity 2-45 within1 week.All of S0,S55,and S60 died,among which S0,S55,and S60 were all lethal time.The specifications ? were 10.33±1.9 h,29.55±3.2 h,12.67±1.6 h,and the specifications ? were1.22±0.5 h.,67.5±4.3 h,3.8±0.9 h.Within 1 week,the survival rates of the size ? and ? squid in the S50 group were 15±7.8%and 30±4.5%,respectively.In the S0 group,the mortality of the two sizes of yellow croaker was 100% within 12 h.Among them,the total lethal time high salt S60 group was significantly smaller than the S55 group,and the higher the salinity,the lower the tolerance.The semi-lethal time(y)and the corresponding salinity(x)are fitted to a quadratic function regression curve,the specification ?:y=-0.199x~2+18.405x-380.75,R~2=0.999,specification ?:y=-0.093 x~2+9.67x-243.5,R~2=0.998.When the salinity exceeds a certain range,the semi-lethal time decreases sharply with the increase of salinity,that is,the salinity tolerance and salinity are significantly negatively correlated.With the increase of salinity,the tolerance is slowly decreased first,followed by a sharp decline.Here,the author concludes that the tolerant salinity of the two species of yellow croaker is not less than 2,and the lower limit of tolerance salinity is not higher than 50.In terms of size,large-scale yellow croaker is more tolerant to salinity than small-sized yellow croaker.2.The effect of salinity on growth,tissue antioxidant enzyme activities and non-specific immunity and metabolic indicators of yellow croaker.In this experiment,five salinity groups,namely S6,S12,S18,S30 and S42,were set up,and each group was three parallel.After 7 weeks of long-term salinity stress experiments,the results showed that:(1)With the increase of salinity,the specific growth rate decreased.(2)Through paraffin sectioning,it was found that the liver tissue of the high-salt group,the low-salt group and the control group were not significantly different;the salinity cells in the sputum tissue increased significantly with the increase of salinity.(3)In this study,the low salt S6,S12 and S18 groups were not significantly different from the control group(P>0.05),while the high salt group S42 was significantly lower than the control group,the liver ratio and the bait coefficient.The changes are consistent.(4)Superoxide dismutase(SOD)in the scorpionfish and liver tissues of S.serrata,S6 and S42 groups were higher than S30 group(control group).The activities of acid phosphatase(ACP)and alkaline phosphatase(AKP)in the scorpionfish were increased with the increase of salinity,but there was no significant difference,but the two enzymes in serum were S6 and The S42 group was significantly lower than the S30 group.The aspartate aminotransferase(AST)activity in the sputum tissue was significantly higher in the S6 group than in the other groups,and the enzyme activity was lowest in the S42 group,while the alanine aminotransferase(ALT)increased first with the increase in salinity,then decreased and then increased.There was no significant difference in serum biochemical index lactate dehydrogenase(LDH)between the groups.The trend of creatinine(Cr)and triglyceride(TG)increased first and then decreased with the increase of salinity.Glucose(GLU)first drops and then rises and then falls.Each metabolic index was the lowest in the salinity group of 42(P<0.05).3.The effect of salinity on the intestinal flora.The experiment was divided into salinity S6,S30,S42 groups,a total of 3 groups,each set of 3 parallel,after 7 weeks of long-term salinity stress experiment,the experiment was over,the microbial diversity of the yellow croaker was taken.The results show that:(1)There are 524 OUT clusters in the S6 group;494 OUT clusters in the S30 group;and 567 OUT clusters in the S42 group.(2)Among the three salinity groups at the gate level,the dominant bacterial populations were mainly distributed in Proteobacteria and Soft Wall bacteria,accounting for 90.79%-98%of the total bacterial OUT in all samples of each group.Among all the bacteria,the S.cinerea and S.microphylla S6 groups were significantly higher than the S30 group;the Bacteroides S30 group was significantly higher than the S6 group.The S42 group was significantly higher than the S30 group.(3)Subordinate level analysis results showed that in S6 group and S30 group,dominant bacteria were Pseudomonas(25.99%and19.06%,respectively),spiroplasma(15.18%and 13.8%,respectively),Burke Genus(14.14%and 18.19%,respectively),Mycoplasma(13.1%and 6.95%,respectively).The dominant bacteria in the S42 group were spiroplasma(24.53%),short-wave genus(19.81%),and mycoplasma(10.66%).There were significant differences in the bacterial content of 25 genera between the S6and S30 groups,and 18 of them were significantly higher than the S30 group.There were significant differences in the bacterial content of 57 genera between the S42 and S30 groups,and37 of them were significantly higher than the S30 group.(4)Species annotation using the latest RDP and NT-16S databases showed that the pathogenic Vibrio was significantly higher in the high-salt S42 group than in the control group(P<0.05),and the red fungus was reduced as a growth factor providing the host.It shows that high salt is not conducive to the growth of N.albiflora. |
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