Study On Carbohydrate Supply,TSS Regulation And Utilization Of Remaining Flocs Of Ictalurus Punctatus Cultured In BFT

Channel catfish（Ietalurus punetaus）is a kind of carnivorous fish.After being domesticated,channel catfish can feed on plant feed,in recent years,Biofloc technology is popular over the world,and the floc is composed of all kinds of microorganisms,zooplankton and plants,residual feed and organic debris,which can be used as the natural feed for channel catfish.It has been proved that it is feasible and efficient to breed channel catfish with BFT,but there are still technical difficulties in the regulation of C/N ratio and Total suspended solid（TSS）in BFT,so a slow released carbon source—3-hydroxybutyrate-co-3-hydroxyvaleric acid copolymer（PHBV）,was added in this experiment to study the influence of PHBV on the growth,water quality and nitrification of channel catfish,in order to find a more efficient regulation of C/N ratio.At the same time,the effects of TSS regulation on the growth,nitrate accumulation and nitrogen budget of channel catfish were studied.In order to explore the best way of TSS regulation for channel catfish growth,the effects of TSS on nitrogen recycling were also explored.In addition,with the maturity of BFT technology and the expansion of its scale,the flocs excluded in the breeding process will also become a major waste of the aquaculture industry.Because of its high protein content,the biofloc is a kind of potential and natural protein source.Therefore,in this experiment,a certain proportion of soybean meal,biological flocs and fermented lactic acid bacteria were added to the commercial feed to study the effect of different feed composition on the growth and enzyme activity of channel catfish,which contribute to the search for new protein sources.This paper mainly focuses on the C/N ratio,TSS regulation technology and the reuse of the remaining flocs in BFT culture system,hoping to provide practical basis and theoretical guidance for BFT technology.1. Effects of PHBV as carbon source on growth,water quality and nitrification of channel catfish in BFT systemIn order to study the effect on water quality、nitrifying rate and enzyme after adding PHBV to bioflo technology system（BFT）,this experiment was divided into two groups,the first group was CL group,which was without PHBV,the second group was PHBV group,hanging PHBV（300 g）with bags.The channel catfish fingerlings were cultured for 28 days.During the experiment,the water quality and floc index were detected every4 days,at the end of experiment weight the fish and the final culturing water was taken for continuous monitoring of degradation of 10 mg/L nitrogen.The content of AMO,HAO and NOR was detected by floc samples at special point.The results showed that there was no significant difference in survival rate,weight gain rate,specific growth rate and feed coefficient between the two groups.PHBV had no significant effect on the growth of channel catfish.TAN and NO₂^--N both were at low level in the whole culturing process,and NO₃^--N,PO₄^3-,TN,TP,TSS and FV of the two groups showed a trend of continuous accumulation.And it took about 28 hours for the two groups to convert 10mg/L NH₄⁺into NO₃^--N,indicating that the flocs of two groups had good performance,but the PHBV group had stronger NO₂^--N buffer ability and was more friendly to the breeding animals.The results of nitrifying enzyme showed The content of AMO、HAO and NOR in PHBV group was significantly higher than that in CL group,the nitrification rate was not significantly increased.In addition,the content of AMO,HAO and NOR in the free bacteria of the two groups were significantly lower than that of the fixed bacteria,and the content of AMO,HAO and NOR in the free bacteria of the CL group did not decrease because they were less than that of the PHBV group.2. Effects of different TSS levels on growth,nitrate accumulation and nitrogen budget of channel catfish in BFT systemIn order to study the effects of regulating TSS level on the growth,nitrate accumulation and nitrogen budget of BFT system of channel catfish,this experiment is divided into three groups,each group has three repetitions,CL group does not add PHBV,does not regulate TSS;CT group does not add PHBV,when TSS reaches 800mg/L,reduced to 500 mg/L;CTP group each hanged PHBV particles（300 g）,when TSS reaches 800 mg/L,reduced to 500 mg/L.The initial TSS was 200 mg/L,30channel catfish fingerlings were put into each tank for 109 days.The results showed that the growth of channel catfish in BFT system was good,and the relative utilization of nitrogen was higher than that in traditional culture mode,but it was not affected by the addition of PHBV and the regulation of TSS.Adding PHBV as a carbon source can reduce the individual differences of adult fish,but it has no effect on the growth of channel catfish.The nitrate accumulation in CT group and CTP group was lower than that in CL group,which indicated that regularation of TSS could slow down the nitrate accumulation to some extent.In addition,CL group had no negative effects on the growth,blood and enzyme activity of channel catfish at high level of TSS（1700mg/L）,so it could reduce the TSS regulation of BFT system of channel catfish in the future.3. Study on the feeding of surplus flocs as supplementary feed in Ictalurus punctatus BFT systemIn order to study the effect of adding biological flocs to feed channel catfish in BFT system on its growth,water quality and enzyme activity.Nine culturing tanks were divided into three groups,each of which had three repetitions.Ten channel catfish fingerlings were put into each tank,the culturing period was two months.The first group was fed with commercial feed,the second group was fed with commercial feed+soybean meal,the third group was fed with feed and dry flocs,the ratio of feed to soybean meal and dry flocs was 2:1,when fed,four days was mixed with 50%of fermented Lactobacillus liquid,and the rest three days were not added.Feed twice a day with a feeding rate of 5%of body weight.Water quality were detected every four days.After the experiment,the fish body was weighed and its length was measured.Results show that the survival rate of the three groups was good,which showed that adding a certain proportion of soybean meal and flocs to the feed could ensure the normal life activities of channel catfish,but from the perspective of growth index,the feed group and feed+soybean meal group had more advantages.From the perspective of water quality index,the feed group and feed+flocs group had better stable effect on water quality.From the perspective of enzyme activity index,the serum SOD value of feed+flocs group was significant higher than the other two groups,indicating that it may have a longer life span.In general,soybean meal and biological flocs are both potential protein sources,but they have their own shortcomings.In the future,we need to strengthen the research efforts,depth,breadth,and strive to improve the strengths and avoid the weaknesses.