| The razor clam(Sinonovacula constricta)is an important economic shellfish in China and widely distributed in intertidal zone and estuarine area.Salinity and density are important influencing factors in artificial culture.The growth and survival of S.constricta would be affected by high culture density or inappropriate salinity.Therefore,it is of great significance to study the optimum salinity and density in the early development of S.constricta.In the present study,we examined the metamorphosis rate and survival rate of larvae,growth and energy metabolism level of juveniles,osmotic regulation ability and antioxidant level of subadults at different density and salinity environment.The aim of this study was to provide some reference for the efficient seedling and cultured technology of S.constricta.1.Effects of salinity on growth and physiological metabolism of S.constrictaThe larvae were taken as experimental objects,and the D-shaped larvae and the umbo larvae were set in four groups with salinities of 8,11,14 and 18,respectively.When the metamorphosis rate reached more than 70%,the experiment was finished.And then,the metamorphosis rate and survival rate of larvae were observed and recorded under a microscope.The results showed that the metamorphosis rate of D-shaped larvae was higher when the salinity was 8 and 11,reaching(79.1%±1.1%)and(78.0%±3.7%),respectively,which was significantly different from that of the other two groups(P<0.05).The survival rate of D-shaped larvae in 11 salinity group was the highest(87.5%±1.1%).The metamorphosis rate of umbo larvae was higher when the salinity was 8 and 11,reaching(74.8%±1.6%)and(72.8%±3.1%),respectively,which was significantly different from that of the other two groups(P<0.05).The survival rate of umbo larvae on the top of shells was the highest(83.5%±1.6%)in 11salinity group.The juveniles were taken as experimental objects.Five salinity groups were set up,which were 12,16,20,24,28 respectively.The culture experiment lasted for 28 days.Growth,Na~+/K~+-ATPase(NKA)activity,hexokinase(HK)activity and pyruvate kinase(PK)activity were detected.The results showed that the specific growth rates of juvenile shell length(SGR)were 6.1%/d,6.6%/d,6.1%/d,5.9%/d and 5.7%/d,and the specific growth rates of body weight(SGR)were 16.5%/d,17.5%/d,16.8%/d,16.3%/d and 16.1%/d,respectively.The shell length and body weight of juveniles grew fastest in 16 salinity group.The activity of NKA decreased firstly and then increased with the increase of salinity.NKA activity in 12 and 16 salinity groups was significantly lower than that in other salinity groups.The activities of HK and PK decreased firstly and then increased following with the increasing of salinity.HK and PK activities in salinity groups 12 and 16 were significantly lower than those in other groups(P<0.05).In conclusion,the optimum salinity range for larvae was 8～11,and that for juveniles were12～16.2.Effects of density on growth and physiological metabolism of S.constrictaThree density groups were set for D-shaped larvae and umbo larvae.The density of D-shaped larvae was 5/m L,10/m L,15/m L,and the density of apical larvae was 3/m L,6/m L,and 9/m L.When the metamorphosis rate reached more than 70%,the experiment was finished.The highest metamorphosis rate was D-shaped larvae with a culture density of 5 larvae/m L(76.1%±0.7%).The survival rate of 5/m L and 10/m L density groups was(87.6%±1.4%)and(86.3%±1.2%),respectively,which was significantly higher than that of 15/m L density group(P<0.05).The metamorphosis rate and survival rate of umbo larvae were higher in 3/m L and 6/m L density groups.The metamorphosis rate was(80.3%±1.6%)and(80.2%±1.2%),and the survival rate was(84.4%±1.7%)and(87.4%±1.6%),respectively.The juveniles were taken as experimental objects.Four density groups were set up,which were 1×10~4 individuals/m~2,1.5×10~4individuals/m~2,2×10~4 individuals/m~2 and2.5×10~4 individuals/m~2,respectively.Growth,amylase activity,cellulase activity,lactate dehydrogenase(LDH)activity and succinate dehydrogenase(SDH)activity were determined.The results showed that the SGR of juvenile shell length was 5.7%/d,5.3%/d,4.8%/d and 4.3%/d,and the SGR of body weight was 14.0%/d,13.2%/d,12.3%/d and 10.2%/d,respectively.The growth rate of juvenile shell length and body weight was the fastest with a density of 1×10~4 individuals/m~2.The amylase and cellulase activities of juveniles decreased with the increase of density,and the amylase and cellulase activities were the highest in 1×10~4 individuals/m~2 density group.The activities of two digestive enzymes were positively correlated with the growth of juveniles.The activity of LDH increased with the increase of density.This group(2.5×10~4 individuals/m~2)was significantly higher than the other density groups(P<0.05).The SDH activity of 1×10~4 individuals/m~2 and 1.5×10~4 individuals/m~2 density groups was significantly higher than the other two groups(P<0.05).In conclusion,the optimal culture density of D-shaped larvae was 5～10/m L,that of umbo larvae was 3～6/m L,and that of juveniles were 1×10~4 individuals/m~2～1.5×10~4 individuals/m~2.3.Effects of salinity and density on osmotic regulation and antioxidant levels of S.constrictaSubadults were taken as experimental subjects,and 4 treatment groups were set up,which were labeled as A(60 individuals/m~2,salinity 20),B(60 individuals/m~2,salinity 30),C(120 individuals/m~2,salinity 20),and D(120 individuals/m~2,salinity30),respectively.Short-term stress test was conducted for each group for 72 h.hemolymph ion concentration,the expression of antioxidant level and ion transport-related genes were measured at 6,12,24,48 and 72 h.The results showed that the concentrations of K~+and Na~+in the hemolymph of group A and C were stable all the time,while the concentrations of K~+and Na~+in the hemolymph of group B and D were gradually increased,and reached the highest at the 12 h and 24 h,respectively,and then stabilized.There was a significant interaction between density and salinity on NKA activity.NKA activity in groups B,C and D was significantly higher than that in group A(P<0.05).At each time point,superoxide dismutase(SOD)activity and malondialdehyde(MDA)content in experimental groups were significantly higher than those in group A,and density and salinity had significant interaction on SOD activity and MDA content(P<0.05).The expression of Na~+/H~+Antiporter gene and V-ATPase gene in all experimental groups were significantly higher than that in group A(P<0.05),the expression level increased firstly and then decreased with time. |
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