| The application of bio-flocculation technology in aquaculture is adjusted the carbon/nitrogen ratio(C/N)of aquaculture water by adding organic carbon sources,to promote the dominant growth of heterotrophic bacteria,and use the total ammonia nitrogen,feces,and residual baits of aquaculture water to reform the bioflocs that can be re-ingested by the cultured animals,to achieve the purpose of improving the utilization of feed protein and purifying the aquaculture water environment.The assimilation of ammonia nitrogen by heterotrophic bacteria in the bio-floc culture system consumes a large amount of organic carbon sources.But the C/N of the feed is far below the requirement for the proliferation of heterotrophic microorganisms,and therefore additional carbohydrates are needed.There has been a lot of research and report on the strategy of adding carbohydrates for biofloc technology system,but the specific method of carbohydrates addition still lacks systematic theoretical guidance.This article focuses on the construction of marine biofloc culture system and explores the effects of nitrogen transformation during the formation of marine biofloc system.Experiments are mainly divided into the following three parts:1.Effect of carbohydrates addition methods on start-up efficiency of marine biofloc technology-aquaculture systemRaising the carbon/nitrogen ratios of Biofloc technology(BFT)aquaculture system by providing carbohydrates can promote the growth of heterotrophic bacteria,and reform bioflocs with feces and lures in cultured water,so as to improve the utilization rate of feed protein and purify the aquaculture water.However,there is no uniform view on how to add carbohydrates.In order to prevent the aquaculture animals from being poisoned by ammonia nitrogen and nitrite nitrogen during the construction of BFT system,it is necessary to set the start-up stage of the BFT system.Therefore,A60 days experiment was carried w out to investigate three strategy of carbohydrates providing at the start-up stage of the biofloc system with salinity of 30 ppt,aiming at optimizing the adding strategy of glucose,so as to shorten the formation period of the biofloc system and stabilize the water quality quickly.The first method is to add glucose to the biofloc technology(BFT)system(group A)at a one-time to make the C/TN(total nitrogen)be 15(group A).The second is 10% total glucose of group A was added every day from 1st to 10 th day,after that,if the total ammonia nitrogen(TAN)increased to above 1 mg·L-1,the glucose was added according to C/TAN of 6.The third is to add glucose every day according to C/TAN of 6.The results showed TAN in A and C treatment groups was generally at a low level during the experiment period.TAN in B group reached a peak value of(16.36±3.02)mg·L-1 on the 31 th days,Nitrite nitrogen(NO2--N)and Nitrate nitrogen(NO3--N)had a significant accumulation,but dropped to the lowest level on the 59 th day.The three treatment groups both had assimilation and nitrification,but the nitrification was obviously inhibited in the system with continuous addition of carbohydrates.The extracellular Polymeric Substances(EPS)and crude protein of bioflcos in the three treatment groups showed the trend of decreasing during the experiment period,and the settling velocity of bioflocs of the three treatment groups becomes better.The bacterial community of bioflocs was analyzed by High-throughput sequencing.The results showed that,at the phylum level the main advantage microflora of the 3 different groups are Proteobacteria.Besides,Bacteroidetes and Planctomycetes were also found in group C.At the class level,the main advantage microflora in group A and group B are mainly Gammaproteobacteria,while the main advantage microflora in group C are Gammaproteobacteria,Alphaproteobacteria,Flavobacteria and phycisphaerae.Thus,continuous addition of carbohydrates can enrich microbial species.The experiment shows that the three carbohydrates additions can stabilize the water quality in about 55 days in a seawater aquaculture systems using bioflocs technology.2.Study on the effects of PHB and glucose as seawater biofloc carbohydrates for breeding Litopenaeus vannameiIn this study,poly-?-hydroxybutyric(PHB)was used as the carbohydrates for the "coarse-age" L.vannamei shrimp in marine BFT system,and glucose was used as a control to explore their best way to add and the effect on the growth performance of the shrimp during the crude period.The results showed that both glucose and PHB could maintain the water quality of the BFT system,and the concentration of TAN and NO2--N remained between 0.1 and 0.3 mg·L-1.After the 10 th day of cultivation,the concentration of NO3--N showed a significant growth trend.The treatment group was a nitrating BFT system.The FV-5min and TSS of the bioflocs were lower in the rear aquaculture period,but the total nitrogen was not decreased,indicating that the nitrogen in the system was accumulated in the water in the form of nitrate nitrogen.After 40 days of culture,the survival rate of the PHB-G group was 66.67%,the highest among the three treatment groups,followed by the PHB-T group,and the survival rate was 62.33%.The survival rate of the two groups was significantly higher than that of the GLU-T group 60 % survival rate.It indicates that PHB is the carbohydrates of the BFT system,which is beneficial to the survival of the“coarse”shrimp.From the final growth index of each group of shrimps,the average weight of the shrimps harvested in the PHG-G group averaged about 1 g,which was significantly higher than the final body weights of the shrimps harvested in the PHB-T group and the GLU-T group(P<0.05).Experiments have shown that the use of PHB in combination with glucose not only meets the need for carbohydrates in a BFT system,but also reduces the stress caused by the addition of glucose and promotes the growth of cultured objects.3.Effect of different Artemia feeding ratios on Seawater biofloc culture systemIn this study,live Artemia larvae and feed were fed at a ratio of 100%,50%,and 0%,respectively,to provide better biological feed for juvenile shrimp,and to use the Artemia ingestion characteristics to stabilize the water quality of the BFT system.Artemia affects the nitrogen conversion pathway and conversion efficiency during the construction of BFT system.The results showed that the concentration of nitrite in the100% Artemia group was significantly lower than that in the other two groups(P<0.05).The ammonia nitrogen concentration in each group peaked on the 7th day of culture,and then decreased rapidly and maintained at 1 mg·L-1.Below,the difference betweenthe three groups was not significant(P>0.05).There was no accumulation of nitrate in the three groups and even present a slight decrease,indicating that the nitrification was not obvious in the BFT system within 30 days.After 30 days of culture,the highest survival rate was 35.67% in 100% A group,and no more than 30% in the other two groups.However,the weight of the shrimp obtained in the 100% A group was only about 2 g,which was significantly lower than the mean value of the 50% AF group(2.985 ± 1.852)g,and the mean value of the 100% F group(3.254 ± 1.225)g.It indicated that Artemia can be used as the best open bait for juveniles,which can increase the survival rate of juveniles.However,in the later stage of culture,Artemia is relatively single,so it is not as effective as nutrient-balanced formula feed in the culture of shrimp.Through comparison of the changes of the three-state nitrogen monitored continuously before and after culture,the rate of conversion of the 10 mg·L-1ammonia nitrogen after the culture of the biofloc system was significantly higher than that before cultivation.The ammonia nitrogen conversion efficiency of 100% of the Artemia group was lower than 50% and 0% of Artemia fed group. |
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