Study On The Relationship Between Scallop Culture And Water Quality Environment

Scallop farming is a pillar industry of mariculture in China and plays an important role in promoting the development of fishery economy.But the increase of farming scale and farming density also brings a series of problems to the breeding environment.Therefore,maintaining the interdependence and mutual utilization between scallop farming and the environment is the main challenge to ensure the healthy development of scallop farming.In this research,the water environment of ponds and aquaculture areas were detected in the intermediate cultivation and cultivation,which explored the key of environmental factors affecting the growth of juvenile scallop and scallops.On this basis,by setting different breeding densities of juvenile scallop and scallops,we compared and analyzed the breeding effects under different densities,and discussed the ecological environment where was suitable for scallop culture technology,so as to maximize the breeding benefit and ensure that scallop breeding does not adversely affect the ecological environment,thus contributing to the development of scallop breeding industry.（1）In order to explore scallop culture density and water quality influenced on the preservation effect of scallop in the middle cultivation stage of Argopecten irradians,three density groups（density group I,density group II and density group III,each with 3 ponds）were set up in Laizhou,Shandong Province from April 6 to May 18,2020.The total number of cages in each group was 504,420 and 360,respectively.The amount of shellfish seedlings was 6.05×10~8,5.04×10~8and 4.32×10~8,respectively.The water quality was tested once every 3 days.The results showed that:the water temperature,salinity,dissolved oxygen and inorganic nitrogen content in each group of ponds were in the appropriate range for the growth of shellfish seedlings;the p H of each pond in density group I exceeded the optimum range in the late and late stage of intermediate cultivation and the p H of each pond in density group II exceeded the optimum range in the late stage;the chemical oxygen demand of each pond in density group I exceeded the standard in the early,middle,late and late stages and in density group II in the middle,late and late stages;the exceeding times of active phosphorus in ponds of density group I and II were significantly higher than those of density group III;the total seedling numbers of each pond in the three density groups were 1.73×10~8～1.84×10~8,2.50×10~8～2.68×10~8and3.02×10~8～3.14×10~8,respectively.The survival rate and total emergence number of shellfish seedlings were in the order of density group III>density group II>density group I;the results of correlation analysis showed that p H,chemical oxygen demand,active phosphorus,the number of cages and the amount of scallop seedlings were negatively correlated with the total number of seedlings.The above results showed that:p H,chemical oxygen demand and active phosphorus were important limiting factors for the effects of pond seedling protection in the intermediate cultivation stage of scallop;it is suggested that the number of cages per mu in the pond is 16,and the amount of seedlings per mu is 1.92×10~7,and the water quality is timely adjusted according to environmental changes,so as to achieve the optimum seedling protection effect.（2）The purpose of this study was to investigate the variation of environmental factors and their effects on scallops in Argopecten irradians culture area.Physicochemical factors,phytoplankton and bacteria were investigated in 13 scallop culture areas of Yantai Sishili Bay and Laizhou Bay from May to November 2020.The nutritional status and water quality of aquaculture area were evaluated by seawater nutritional status index method and Nemerow environmental quality comprehensive index method.Evaluation of phytoplankton community structure by phytoplankton diversity index（H’）,evenness index（J）and richness index（D）.Correlation analysis and canonical correspondence analysis of environmental factors,physicochemical factors and dominant species of phytoplankton were performed using SPSS 25.0 and Canoco 5.0 software.The results showed that:water temperature,p H,salinity,dissolved oxygen and chemical oxygen demand in each culture areas met the second class of national water quality standards;active phosphorus and total phosphorus met the second class of national water quality standards except for some farming areas in partial months;nitrite,nitrate and ammonia nitrogen in each culture areas were within the safe concentration range;inorganic nitrogen only part of the Laizhou Bay aquaculture areas beyond the national second class water quality standards;the results of N/P showed that there were both phosphorus limitation and nitrogen limitation in Sishili Bay,and phosphorus limitation was main in Laizhou Bay;the average of phytoplankton density in the two sea areas was 22.28×10~4cells/L and 18.40×10~4cells/L,respectively;a total of 71 phytoplankton species belonging to 5 phyla were detected,including 45diatoms,accounting for 63.38%of the total species;the average values of diversity index,evenness index and richness index in Sishili Bay were 2.23,0.80 and 2.72,respectively,while those in Laizhou Bay were 2.24,0.77 and 2.82,respectively;the average values of heterotrophic bacteria and Vibrio in Sishili Bay were 2450 cfu/m L and 2805 cfu/m L,respectively,while those in Laizhou Bay were 308 cfu/m L and 481 cfu/m L,respectively;the correlation analysis results showed that water temperature was correlated with dissolved oxygen and bacteria,and phytoplankton density was correlated with p H,phosphorus and nitrogen nutrients;the results of canonical correspondence analysis showed that water temperature,p H,dissolved oxygen and active phosphorus were the main factors affecting the growth of dominant species of phytoplankton.The above research results showed that:the physicochemical factors in each culture area were at a reasonable level except that the phosphorus and nitrogen nutrients exceeded the standard in some months;the phytoplankton community structure was complex,the species were abundant and evenly distributed,and the water quality was clear,which was suitable for the cultivation of Argopecten irradians;but the formation of absolute dominant species of phytoplankton in some months in the Sishili Bay affected the stability of community structure,and most dominant species of phytoplankton in the two sea areas were not easy to be fed by scallops,which may affect them.（3）The effects of breeding density on scallop growth were analyzed to explore the suitable breeding density for the environment in the breeding areas.Three scallop culture density groups were set up in two culture areas（S1 and S3）of Yantai Sishili Bay,with cage spacing of 0.4 m,0.6 m and 0.8 m,respectively from May to November 2021.The results showed that:there was little difference in water temperature,p H,dissolved oxygen and chemical oxygen demand between the two farming areas,but the density of active phosphorus,inorganic nitrogen and phytoplankton in S1 farming area was significantly higher than that in S3 farming area;the growth rates of shell length,shell height and shell width of scallops in different density groups were faster from May to July,slower from July to September,the slowest from September to November,but the body weight increased significantly in the following months;after six months of cultivation comparison,scallops in the two cultivation areas showed the characteristics of decreasing shell length,shell height,shell width and body weight with the increase of cultivation density;the growth traits of scallop in S1 culture area in September and November of 0.4 m group were significantly less than those in 0.6 m group and 0.8 m group（P<0.05）.Although the former was less than the latter,the difference between 0.6 m group and 0.8 m group was not significant（P<0.05）;the growth traits of scallop in S3 culture area in September and November of 0.4 m group were significantly lower than those in 0.6 m group,and those in0.6 m group were also significantly lower than those in 0.8 m group（P<0.05）;in S1culture area,scallop showed the characteristics that the column yield and the output value of single cage decreased with the increase of culture density,and however,the output value and benefit of single raft in 0.8 m group and 0.6 m group were better than those in0.4 m group,but the output value and benefit of single raft in 0.6 m group were better than those in 0.8 m group;in S3 culture area,the yield of single cage,output value of single cage,output value of single raft and benefit of single raft decreased with the increase of culture density.The above research results showed that in the S1 culture area with high phytoplankton density,the density with cage spacing of 0.6 m could be used for breeding,but in the S3 culture area with low phytoplankton density,the density with cage spacing of0.8 m should be used for breeding,so as to achieve the best breeding effect of Argopecten irradians.