The Effects Of Stocking Density On Growth,Survival,Stress In Marsupenaeus Japonicus

Marsupenaeus japonicus is most important shrimp in China.Because of gorgeous color,endurance of drying,they are usually sold by high price with living.However,contrast to other common shrimp,for example Litopenaeus Vannamei and Penaeus monodon,the unit production of M.japonicus is lower.Stocking density is one of the most factors to affect the unit production of M.japonicus,and the growth and survival of M.japonicus are influenced by stocking density directly or indirectly.In actual farming shrimp,the suitable density can not only make full use of the water,but also reduce the rate of disease outbreaks due to environmental degradation.On the other hand,the too high or low stocking density can reduce the unit production,but also increase the risk of farming and reduce the profits of farming.Because of many advantages of biological floccules technology,stabilizes water quality,supplements bait and increase unit production,we study the suitable stocking density of M.japonicus under the environment of biological floccules.The experimental materials of this study are juvenile shrimp of M.japonicus(initial average weight,initial average body length and initial average carapace length are 0.034±0.007g,1.55±0.11cm and 0.42±0.065cm respectively)and five density gradients are designed:A(20/m3),B(40/m3),C(80/m3),D(130/m3)and E(260/m3).Every density has three experimental ponds and there are 15 experimental ponds totally.So we study the effects of stocking density on M.japonicus under the condition of biological floccules.The three results are as follows:1.The fluctuation of water factors under the condition of biological floccules:The changes of water factors under the condition of biological floccules in different density groups are not significant,and the water temperature and pH keep about 28±1℃ and 7.9±0.3 respectively.The salinity is decrease during farming period until reach to 25‰,due to continuous rainfall in summer season.At the same time,the changes of ammonia nitrogen and nitrite tend to be consistent,and in the first two weeks,the concentrations of ammonia nitrogen and nitrite increase rapidly until reach to 2 mg/L and 0.30 mg/L respectively.During 60 days experiment span,all water factors always keep suitable range for M.japonicus,and have no navigate effects on farming M.japonicus.2.The effects of stocking density on growth characteristics,survival and antenna injured in M.japonicus:During experiment,the weight,body length and carapace length efficiency decrease as the density increaser,and stocking density has significant effect on survival and antenna injured(P<0.05).In the end of this experiment,the survival rates of M.japonicus in different densities are 35%(E),54%(D),54%(C),65%(B)and 85%(A)respectively,and the antenna injured rates of M.japonicus in different densities are 76%(E),74%(D),53%(B),12%(C)and 7%(A).3.The effects of stocking density on stress-related genes expression in M.japonicus:(1)Heat Shock Protein,HSP:the stocking density has significant effect on gene expression of three HSPs(HSP60,HSP70 and HSP90)(P<0.05),and the expression of three HSP increase as the density increaser.And furthermore,the expression of three HSPs in M.japonicus with antenna injured(D)is higher than antenna unbroken(W).Contrast to HSP60 and HSP90,the relative expression level of HSP70 is much higher.This result shows that HSP70 is more sensitive when M.japonicus is suffered from density stress.(2)Oxidative Stress:the stocking density has significant effect on relative expression of three genes about oxidative stress(P<0.05).The relative expression of nicotinamide adenine dinucleotide phosphate(NADPH)increase as the density increaser and it’s relative expression in M.japonicus with antenna injured is higher than antenna unbroken organisms.However,two Superoxide dismutases(MnSOD and Cu-ZnSOD)show different trends in antenna injured and antenna unbroken individuals.in antenna injured individual,the relative expression of SOD increase as the density increase,however,in antenna unbroken individual,the relative expression of SOD decrease as the density increase,and the increasing trend of NADPH expression is higher than SOD.Moreover,in low stocking density group,the relative expressions of NADPH and SOD at lower level and it suggest that M.japonicus was less density stress in low stocking density group.