Effects Of Sediment On Growth,Physiological Metabolism And Burrowing Behavior Of Sinonovacula Constricta

Sinonovacula constricta is a kind of marine bivalve shellfish that lives in the coastal or inner bay mudflat.It has the characteristics of fast growth,high yield,low breeding cost,etc.The sediment is an important place for buried shellfish to filter and inhabit,and plays an important role in the ecosystem,which has different degrees of influence on the water body and biological growth.On the one hand,the bottom microorganism can transform the organic matter in the water body and promote the flow of nutrients between the water bodies;On the other hand,the sediment can affect the osmotic regulation,energy consumption and physiological metabolism of benthos,and directly affect the growth,development and reproduction of organisms.Therefore,the sediment plays an essential role in the proliferation or artificial breeding of shellfish in natural waters.In this paper,the suitable sediment of S.constricta at the early growth and development stage（larva and juvenile shell）were studied,and the burrowing behavior and feeding ability of different sizes of juvenile shell under different sediment conditions were compared.Finally,the growth and physiological metabolism indexes of S.constricta at different sediment thickness were analyzed.It provides reference data for the setting of sediment conditions for early culture of S.constricta in the process of artificial breeding,the type of sediment suitable for burrowing and the minimum thickness of sediment required in pond culture,aiming at reducing the cultured cost and increasing the cultured yield.1.Taking S.constricta as the experimental object,a single factor experimental design was used to study the effects of different mud laying thicknesses（no mud,1.2mm,2.4mm）in the shell top larval and different sediment types（The sediment concentration gradient is 0%,25%,50%,75%and 100%）in the juvenile stage shellfish on its growth and survival.The results showed that the optimum mud thickness during metamorphosis of shell top larvae is 1.2 mm.Under this condition,the metamorphosis and survival rate were the highest,91.11%and 87.89%,respectively.When the mud thickness was 0 mm,the daily growth rate and daily growth amount of shell length and height were significantly lower than those of other groups（P<0.05）,There was no significant difference between 1.2mm and 2.4mm groups（P>0.05）;The growth of juvenile shellfish has obvious mud tendency.The highest survival rate of all mud sediment is 87.67%,which was significantly higher than that of all sand sediment 52.22%（P<0.05）.Under the condition of all mud sediment,the daily growth rates of shell length and height of juvenile shellfish were 35.95μm/d and 20.55μm/d respectively;Considering the influence of substrate conditions on survival rate and growth,the optimum sediment conditions for S.constricta in the early stage of medium culture were all mud and the thickness of mud was 1.2 mm.2.Taking S.constricta as the experimental object,the effects of different sediment types（total mud,1/3 sand,2/3 sand,total sand）and sediment thickness（6,12,18,24,30 cm）on burrowing and feeding rate of S.constricta（shell length 2.5,3,3.5 cm）were studied.The results showed that:At 25℃water temperature and 20 salinity,the size and sediment type had a very significant interactive effect on the burrowing rate and time（P<0.01）,and the burrowing rate decreasing with the increase of sediment concentration.When the sediment concentration was greater than 30%,the burrowing behavior of S.constricta was obviously blocked,and the burrowing rate of S.constricta of three sizes reached 100%only in total mud within 24 hours.There was a significant difference in the half shell vertical time(ET₅₀)between different sizes（P<0.05）.The larger the size,the longer the time required for burrowing behavior.Sizes and sediment thickness have no significant interaction on the burrowing rate,burrowing time and feeding rate（P>0.05）.The burrowing rate and time under different sediment thicknesses were only related to individual size,but the burrowing depth increasing with sediment thickness.The larger the size was,the deeper the burrowing depth was.The 3.5 cm shell length of S.constricta was about 2/3 of the thickness of the sediment.The feeding rate increasing with the increase of sediment thickness.The feeding rate with a thickness of more than 18 cm was significantly higher than that of the other two types of thickness（P<0.05）,and the feeding rate of 3.5 cm shell length with a thickness of 18 cm was 2.12 times that of 6 cm.The feeding rate was the highest when the shell length was 2.5 cm under the 6 cm thickness of the sediment.Therefore,it is easier to complete the burrowing quickly by selecting the whole mud sediment during the bottom seeding and multiplication of S.constricta,and the breeding depth should be more than18 cm to ensure its normal feeding ability.3.Taking S.constricta as the experimental object,the effects of different sediment thickness（6,12,18,24,30 cm）on the growth and development,oxygen consumption and ammonia excretion rate,respiratory enzyme activity and Ca²⁺/Mg²⁺-ATPase activity of S.constricta were studied under natural pond culture conditions.The results showed that:The growth index and specific growth rate of the 24 and 30 cm thickness groups were significantly higher than those of the 6,12 and 18 cm groups（P<0.05）,and there was no significant difference between the 24 and 30 cm groups（P>0.05）.The survival rate of S.constricta gradually increasing with the increase of the sediment thickness.The highest survival rate was 65.44%in the thickness of 30 cm.The survival rate of S.constricta in the 24 and 30 cm groups was significantly higher than that in the6,12 and 18 cm groups（P<0.05）.There was no significant difference between the 24and 30 cm groups（P>0.05）.The oxygen consumption rate and ammonia excretion rate of S.constricta in the five thickness groups increased first and then decreased.At 40days,the oxygen consumption and ammonia excretion rate in the 24 and 30 cm groups were significantly higher than those in the 6 and 12 cm groups,and the 6 and 12 cm groups were lower than the initial oxygen consumption and ammonia excretion level.The changes of alkaline phosphatase（AKP）activity and lactate dehydrogenase（LDH）activity are positively correlated with the sediment thickness.The activities of AKP and LDH in the 24 cm and 30 cm thickness groups were higher than those in the other three groups,and the difference was significant（P<0.05）.The activity of succinate dehydrogenase（SDH）increased at first and then decreased with the increase of the sediment thickness.The activity of 18 cm group was the highest and significantly higher than that of 6,12 and 30 cm groups（P<0.05）.The change trend of Ca²⁺/Mg²⁺-ATPase activity is consistent with that of SDH,and the activity of 18 and 24 cm thick groups was significantly higher than that of 6 and 12 cm thick groups（P<0.05）.According to the growth and physiological metabolism of the five thickness groups,in the natural culture of S.constricta,the thickness of the sediment should be more than18 cm.