Biofloc Changes In Community Structure And The Effects Of Addition Of Biofloc On Growth Perfomance And Metabolism Of Crucian Carp

With the continuous development of the aquaculture industry, especially intensivefarming, high feed rate and high water exchange rate of the traditional farming model hasbrought great pressure to the protein feed ingredients and culturing environment. Aquaticanimal feed utilization rate is only20%-30%, large-scale cultivation will bring lots of feedresidues to the farming environment. Bio-floc technology based on sewage treatmentprinciple, studying the structure of microbial community，water quality parameters and theeffect of biofloc addition on carp growth, biological characteristics, conventional bodycomposition, liver anti-oxidation index were studied in this paper; expecting to use biofloctechnology better and investigating the value of biofloc of feed ingredients; The experimentresults s howed as follow:（1） Manipulating the carbonrnitrogen ratios of20:1with carbohydrate （glucose）in grasscarp （121.61±14.23g） ponds, the satiation feeding method with crude protein30%ofcommercial feed was conducted.The cultivating period was30days. During the breeding thewater quality was monitor-ed:the concentration of ammonia nitrogen （NH₄⁺-N）, nitritenitrogen （NO₂^--N）, nitrate nitrogen （NO₃^--N）, dissolved oxygen （DO）, total suspended solids（TSS）, alkalinity were measured, meanwhile, using PCR-DGGE （denaturing gradient gelelectrophoresis） to analyse bacterial community structure of biofloc of0,5,10,15,20,25and30days. The results show that：from the beginning to the6th day of experiment, the alkalinityof the water and nitrate was significantly （P <0.05） increased and reached its peak in the firstsix days， the concentration of TSS arrived peak in the9th, and it was significantly （P <0.05）increasing of this period. During the entire experiment, the biological floc nitrate in waterranged from5.60mg.l^-1to14.90mg.l^-1, alkalinity ranged from136.68mg to239.20mgCaCO3.l^-1, TSS concentration ranged from41mg.l^-1to408mg.l^-1. The concentrationof ammonium nitrogen, nitrite nitrogen, alkalinity peak of biofloc water were significantlydecreased （P<0.05）, and then trended to stabilized gradu-ally. PCR-DGGE analysis showedthat20destination bands represent the main part of the alpha-proteobacteria,beta-proteobacteria, gamma-proteobacteria, delta-proteobacteria, Actinobacteria andBacteroides.Actinomycetes, Bacteroides and beta-proteobacteria were the major bacterial groups ofbiofloc forming process. The study results may provide the theoretical basis andreference materials for biofloc technology applications.（2）To study the effects of biofloc addition on growth performance, body compositionand antioxidant parameters of juvenile crucian carp（Carassius cuvier）, A total of300cruciancarp juveniles （body weight （3.24±0.27）g） were randomly assigned into five groups withtriplicate,the basal diet0（Ⅰ） for the control group,10%（II）,15%（III）,20%（IV） fourlevels.Crucian carp juveniles were reared in an indoor aquarium for56days. The resultsshowed that weight, weight gain, specific growth rate of the group Ⅱ were significantly （P <0.05） higher than the other groups, fat index, intestinal index and spleen index did notsignificant difference （P>0.05） among treatment; the liver index in group Ⅱ wassignificantly lower than other groups; the crude fat of whole fish and hepatopancreas ofcontrol group were significant （P <0.05） higher than the treatment group,but not significant（P>0.05） differences in all treatment groups; the feed coefficient of group Ⅱ was significant（P <0.05） difference than the control group; the crude protein of muscle with biofloc additionwere significantly （P <0.05） increasing, and significantly （P<0.05） higher than that of thecontrol group; the value of T-SOD, GST, CAT in hepatopancreas were increased and thendecreased with bio-floc addition,meanwhile,each treatment group was significantly （P <0.05）higher than that in control group; MDA of Ⅱ group was significantly lower （P <0.05） thanthe control group and the rest group, Ⅲ, Ⅳ and the control group had not significantdifference （P>0.05）. Under these experimental conditions, considering the growthperformance, body composition and antioxidant parameters,diets with10%of the biofloc canpromote crucian carp growth performance and liver antioxidant function, reduce feedconversion rates, thereby reducing feed cost.Conclusion:①Alkalinity is a condition for the proliferation of bacteria before reachingthe peak; Actinomycetes, Bacteroides and Proteobacteria the process of major bacterialgroups of biofloc formation;②Appropriate amount of biofloc can promote growthperformance of carp crucian, and the addition is about10%better.