| Macrobrachium rosenbergii is the main shrimp in freshwater culture in China.In recent years,because of its obvious biocontrol effect on Litopenaeus vannamei in mixed pond,it has been rapidly promoted in shrimp culture in some low salinity areas.At the same time,at present,a large number of salt-alkali lands in China can be transformed into low-salinity aquaculture ponds to carry out aquaculture,and egg-holding parent shrimp in breeding stage of Macrobrachium rosenbergii are raised in a certain salinity water body,which is conducive to embryo development.Although there are studies on the effect of salinity on Macrobrachium rosenbergii,there are few reports.So different salinity water feeding Macrobrachium rosenbergii,salinity to Macrobrachium rosenbergii growth,molting and related metabolic enzyme activities,to explore the low salinity stress on Macrobrachium rosenbergii molting and the influence of oxidation resistance,etc,for Macrobrachium rosenbergii in low salinity shrimp shrimp collection,saline-alkali land farming and seedling breeding to provide the reference,the specific studies are as follows:A total of 300 healthy Macrobrachium rosenbergii were selected for the experiment according to the preset salinity gradient(freshwater control group,3,6,9,12),and 5 replicates were set for each salinity group.The molting data of Macrobrachium rosenbergii were analyzed by recording the molting data of each shrimp completely once in the experimental environment.The results showed that with the increase of salinity,the molting cycle lengthened,the daily molting rate changed little,and the molting weight gain rate decreased.The duration of molting interval in group 6 salinity was the longest,which was significantly higher than that in control group.The molting weight gain rate decreased with the increase of salinity,and the molting weight gain rate of 6,9 and 12 groups was significantly lower than that of the control group,indicating that the molting weight gain rate of Macrobrachium rosenbergii was significantly inhibited when the salinity was 12In this paper,the relative gene expression levels of juvenile hormone epoxy-hydrolase(JHEH)and ecdysone receptor(Ec R)in gill tissue,molt-inhibiting hormone(MIH)and retinoic X receptor(RXR)in hepatopancreas tissue,and Chitnase3B(Chitnase 3B)in muscle of Macrobrachium rosenbergii in different salinity water bodies were measured.To analyze the effects of salinity on the expression levels of growth and molting related genes in Macrobrachium rosenbergii.The results showed that the relative expression of molt-inhibiting hormone(MIH)gene decreased from A stage of late molting to D stage of early molting under the same salinity condition.In the control group and 3 salinity condition,the expression level of late-molting was significantly higher than that of inter-molting.The expression level of Retinoic X receptor(RXR)gene was the highest in C stage of molting,and the expression level of other molting stages was significantly lower than that in C stage.The expression of juvenile hormone epoxy-hydrolase(JHEH),a juvenile hormone,was highest in the early stage of ecdysis compared with the C stage of inter-molting.The expression level of ecdysone receptor(Ec R)in branchial tissues of Macrobrachium rosenbergii was significantly higher than that of control group at 3,6 and 12 salinity conditions.These results indicated that chronic low salinity stress had significant effects on the growth molting of Macrobrachium rosenbergii,resulting in decreased weight gain rate and prolonged molting cycle,which had negative effects on production practice.The salinity in the group molting hormone(MIH)inhibition gene expressed in this early phase D minimum relative expression,retinoic X receptor(RXR)gene expression in this stage between C is highest,the salinity of molting hormone(MIH),retinoic X receptor(RXR)gene regulation had no significant effect,but this stage have affected significantly on its amount of expression.The expression levels of ecdysone receptor(Ec R)and juvenile hormone epoxy-hydrolase(JHEH)genes were significantly affected by salinity,indicating that salinity inhibited the expression of growth-related genes.The highest expression of Chitnase 3B gene was found in the D stage of molting in all salinity groups,indicating that Chitnase 3B gene regulates molting activity of Macrobrachium rosenbrachium.The expression of genes related to growth and molting of Macrobrachium rosenbergii under different tissues and salinity was investigated.The results showed that the relative expression level of MIH gene in all salinity groups decreased significantly with the prolongation of molting time,and in salinity groups 0 and 3,the expression level of MIH gene in late molting period was significantly higher than that in inter-molting period,indicating that the expression level of MIH gene in late molting period was higher than that in inter-molting period.The expression of RXR gene was highest in inter-molting period,and significantly lower in other molting periods than in control group.Compared with the control group,the expression level of JHEH in all salinity groups was highest in the early stage of molting.The expression of Ec R gene in gill of Macrobrachium rosenbergii was significantly higher than that of the control group at the salinity of 3,6 and 12 groups.Chronic hypo salt stress significantly affected the molting of Macrobrachium rosenbergii,resulting in decreased weight gain rate and longer molting cycle,which had negative effects on production practice.The relative expression of MIH gene was the lowest in the early stage D of molting,and the RXR gene was the highest in the inter-molting stage C,indicating that salinity had no significant effect on the regulation of MIH and RXR genes,but had a significant effect on the molting stage.The regulation of Ec R and JHEH genes was significantly affected by salinity,indicating that salinity inhibited the expression of growth-related genes.Chitnase 3B gene had the highest expression in the early stage D of molting in all salinity groups,indicating that Chitnase 3B gene had a significant effect on molting.Low-salt chronic stress had significant effects on the gill filament structure of Macrobrachium rosenbergii.A large number of epithelial cells,B cells,R cells and E cells in the gill membrane structure were exfoliated,incomplete and irregular.However,for the structure of hepatopancreas,there were significant changes in the long-term chronic stress of 9and 12 salinity,and the pancreatic duct was enlarged compared with the control group. |
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