| Megalobrama amblycephala,which was commonly known as Wuchang fish,has become a major freshwater fish in China due to delicious meat,fast growth and a high economic value.With the development of intensive aquaculture,in addition to the external environment factors,Bream farming is facing a growing number of ecological and technical issues,it is an important way to development efficient water quality management for maintaining the sustainable development of fish aquaculture.Proposed bio-floc technology meets the requirements of healthy aquaculture,its successful application in Litopenaeus vannamei,tilapia and other aquatic animals that provides a reference for the bream farming.In the paper,we study the water quality control and the contribution of proteins on M.amblycephala that based on the bio-floc technology.We assessed the immunity system and antioxidant enzyme activities in M.amblycephala and dietary supplementation with Bacillus on the effect of growth performance and the intestinal microflora in order to study the bio-floc microbial community structure provides reference material impact on its nutritional value.The research contents are as follows.1.An 8-week trial was conducted to investigate the effects of five carbon sources on the growth performance,intestinal biochemical parameters and water quality in the juvenile M.amblycephala by the principle of bio-floc technology(BFT).The carbon sources include starch(control),glucose,sucrose,sodium cyclamate,composite carbon(mixture of starch and glucose in proportion of 1:1).The results of this study showed that bioflocs could effectively regulate water quality,as well as reduce ammonia and nitrite concentration.Final body weight,weight gain rate(WGR),specific growth rate(SGR)of glucose group was significantly higher than other groups(P<0.05),while feed conversion ratio was significantly lower than other groups(P<0.05).Furthermore,no significant differences(P>0.05)were observed for the survival rate and the body composition of fishes among all treatment groups.Intestine microstructure observation showed that there were some bioflocs in the brush border of intestine in juvenile M.amblycephala.The activities of protease and amylase of fishes in the composite carbon group were significantly higher than control group,glucose group and sucrose group(P<0.05).The activities of superoxide dismutase and catalase of fishes in the composite carbon group were significantly higher than that of control group,however,the malondialdehyde content was significantly lower than that of control group(P<0.05).2.The effect of different dietary protein levels(20%,25%,30%,35%)on growth performance,feed utilization,digenstive enzymes activity,antioxidant enzymes system and the activity of the immune system on M.amblycephala in biofloc-based zero-water exchange culture tanks.The control group was operated with water exchange and fed with 35%protein feed,and the experiment last for 8 weeks to assess the protein contribution to M.amblycephala in the bio-floc culture system.The results show that:(1)The differences on the final body weight,weight gain,specific growth rate and the feed conversion ratio between the treatment groups was not significant(P>0.05)on M.amblycephala.The survival rate in the BF-25%group and recirculating aquacultural system(RAS)group was significantly higher than the BF-30%(P<0.05).Compared with the BF-20%group and BF-35%group,there was no significant difference(P>0.05)on the survival rate.The results showed that there was no effect on the growth and survival at a lower level of dietary protein on M.amblycephala;(2)A11 the treatment groups showed a higher hepatosomatic index(HSI)than the control group,but the BF-20%and BF-25%group had a significantly higher HSI than the RAS group(P<0.05).BF-30%and BF-35%had no significant differences compared with the remaining three groups(P>0.05).There was no significant difference on condition factor(CF)between all the groups.The lipid and moisture of BF-20%were significantly higher than the other groups,but there was no significance on the crude protein content between the groups.The result showed that the bioflocs promote the utilization of fat on M.amblycephala.The activity of amylase in RAS group was significantly higher than the other treatment groups(P<0.05)and the activity of total protease in BF-30%was significantly higher than the BF-20%,BF-25%and RAS group(P<0.05).The result showed no significant differences between BF-30%and BF-35%(P>0.05).The activity of Lipase between the treatment groups showed no significant difference(P>0.05),which showed that there was no effect on digestive enzyme activity of M.ammblycephala;(3)The result of antioxidant enzyme system showed that the bioflocs had an active effect on the antioxidant system of M.amblycephala.But the decreased protein level of 20%showed a possibility that a positive effect would display on the antioxidant system of M.amblycephala;(4)The biofloc could promote on the water quality in the zero-water exchanged culture system.The biofloc technology also can maintained the water temperature at a lower level.3.Studies have revealed that probiotic-enriched diets can have beneficial effects for aquaculture,by enhancing growth and improving disease resistance in cultivated fish species.In this study,we assessed the effects of dietary supplementation of the probiotic,Bacillus subtilis,on the physiology of juvenile blunt snout bream(M.amblycephala).We assessed changes in growth,composition of gut microbiota,and antioxidant activity in fish fed four different experimental diets containing three graded levels of B.subtilis at 2×109 CFU/g(1,10,100g · kg-1 diet)and control diet with no probiotic.The gut microbiota was analyzed at the end of the feeding trial(56 days)with 16S rDNA denaturing gradient gel electrophoresis(16S-DGGE).(1)We report that juvenile M.amblycephala fed a probiotic-enriched diet exhibited a greater final body weight,increased weight gain rate,increased specific growth rate and had enhanced antioxidant activity than did fish on the control diet.This effect was most prominent for intermediate levels of probiotics and was inhibitory at high probiotic levels.(2)Superoxide dismutase(SOD),peroxidase(CAT),glutathione peroxidase(GSH-Px)of T2 group were significantly higher than T1 group(P<0.05),malonaldehyde content(MDA)of T2 was significantly lower than T1 group(P<0.05),showed B.subtilis added 1g/kg can increase the activity of the antioxidant enzyme systems of M.ambly cephala;(3)We also found that this effect may be due in part to the comparatively higher diversity of beneficial bacteria in the gut of the individuals fed a probiotic-enriched diet.The results of this study,therefore,suggest that the addition of dietary B.subtilis at 0.01%dry weight inclusion level may enhance growth and feed utilization of M.amblycephala juveniles and should prove beneficial to the sustainable development of the aquaculture of this species. |
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