Separation And Purification Of A Cyclotella Meneghiniana And Its Application In Coupled Culture Of Fish, Shrimp And Shellfish

The pollution of aquaculture sewage,which is getting worse in the last decades,has become the third major marine pollution in China after domestic pollution and industrial pollution.High-density intensive aquaculture wastewater,especially industrialized aquaculture,and high-density artificial breeding,are directly discharged in large quantities,which brings eutrophication and other serious environmental pollution problems in coastal area.The key to healthy sustainable development of aquaculture is how to treat and utilize the wastewater.Here we introduce a coupled culture model of fish and shrimp shellfish,and analyze the phytoplankton community of aquaculture ponds,and isolate a dominant species of Cyclotella meneghiniana from the algae community to discuss the results of water purification and utilization in this model,which are as follows:1.Analysis of Phytoplankton Community in Fish and Shrimp Mixed Culture PondsThe composition of phytoplankton in fish and shrimp mixed culture ponds consists of a total of 50 species of 33 genera.The Bacillariophyta has 24 species of 15 genera,accounting for 48%of the total phytoplankton species,and Chlorophyta is around about 32%of the total species with 16 species of 10 genera.Finally,Bacillariophyta,Euglenophyta,and Chrysophyta appear to less than Bacillariophyta and Chlorophyta,only making up 12%,4%,and 4%of total,respectively.Chlorella sp.,Chroococcus minutus,Cyclotella meneghiniana are determined to be the dominant species according to the dominance.According to the change of daily feeding biomass of shellfish seedlings,it is clear that Cycllotella meneghiniana is one of the main food organisms for Ruditapes philippinarum.2.Separation,Purification,Culture and Identification of C.meneghiniana in Zhaoan(Dongshan county)The pure unicellular algae were isolated from the fish and shrimp mixed culture pond by the water droplet separation method and the microtubule separation method.The algae was confirmed as C.meneghiniana by the morphological and molecular identification after separation and purification,this is a algae from Zhaoan(Dongshan County).Homology and genetic distance analysis were carried out on 18S rRNA and rbcL gene of this alga,in which the 18S rRNA sequence was 0.002 and the homology was 99.8%from the sequence of five species of C.meneghiniana from GenBank.The genetic distance between the rbcL sequence and the five species of C.meneghiniana from GenBank was between 0.05 and 0.06,and the homology was between 99.4 and 99.5%.Combined with the analysis of homology and genetic distance of the two genes,there was no genetic difference between DH1 and the five strains of C.meneghiniana,or the genetic difference was very small,indicating hat these five strains of C.meneghiniana may have a common origin.In addition,the comparison of genetic distance and homology between DH1 and other seven species of Cyclotella showed that there were some genetic differences between DH1 and different Cyclotella.Thus,the results of genetic distance and homology analysis are consistent with the relationship between DH1 and these twelve species of Cyclotella on the evolutionary branches shown by phylogenetic analysis.3.Study on Water Quality Change in Coupling Culture Model of Fish,Shrimp and ShellfishRegarding the water purification rate in this coupled culture model,the average purification rate of suspended matter,chlorophyll a,inorganic nitrogen,COD,total nitrogen,total phosphorus,active phosphate were 75.61%,72.81%,67.37%,47.89%,38.10%,21.56%,and 4.49%,respectively.Compared with the coastal seawater outside,these parameters are significantly reduced,thus the sewage will not cause pollution.And after continuous observation for five days,shellfish feeding was normal and net weight gain could reach 1.9 kg.The weight of shellfish seedling increased by103.87%after 5 days of intermediate cultivation,which realized the resource utilization of fish and shrimp breeding tail water.Therefore,the seawater cultivated by the algae can be used for the rearing of shellfish seedlings,which provides sufficient nutrients for the growth of shellfish seedlings and has considerable economic value.The combination of coupling culture mode and shrimp farming wastewater purification technology,the combination the wastewater purification method with aquaculture,and the three breeding modes of factory farming,fish-shrimp pond polyculture and shellfish intermediate cultivation can form a high-efficiency purification mode to realize stepwise purification of aquaculture wastewater.Understanding filter-food selection of Ruditapes philippinarum larva to microalgae is of great guiding significance for promoting high and stable yield of seedlings.Meanwhile,filter-feeding of microalgae by shellfish larva can effectively reduce the turbidity and improve the quality of the seawater,which plays a important role in water purification.It can provide a more effective solution for reducing the waste of resources and wastewater pollution in the aquaculture industry,which is beneficial to reduce the cost of aquaculture and wastewater purification and raising the output of breeding to achieve a higher economic benefit.