Effects Of Compensatory Growth On Floc Formation,Microflora Structure And Phytoplankton In Aquaculture Water Of Litopenaeus Vannamei

In order to evaluate the effect of compensatory growth combined with biofloc technology on the water quality of Litopenaeus vannamei,the effects of compensatory growth on the biofloc formation,the microflora and phytoplankton structure were investigated.The shrimps were randomly assigned to four groups with three replicates:Group 1 was the control group,normally fed with commercial diet.Group 2 was the biological floc group,fed with shrimp feed and brown sugar which added 70%of feed,and the aquaculture water C/N ratio was 12.Group 3 was the probiotic and biological floc group,fed with feed and brown sugar,added Bacillus licheniformis（concentration was 1.2×10⁵CFU/m L in water）;Group 4 was the compensatory growth group,intermittent starved for 2 day and re-feeding for 5 days.Feed twice at 8:00am and 17:00 PM each day with 10%of body weight.The experiment period was 28days.The results were as follows;1.During the experiment,the biological floc sedimentation in aquaculture water showed an increasing trend.At the 4^thweek,the formation of biological floc in group 2,3 and 4 were significantly higher than that in group 1（P<0.05）.2.The results showed that OTU of microflora in group 1,group 2,group 3 and group 4 were 3501,6386,5387 and 6577 respectively with high throughput sequencing.The unique OTU numbers were 165,463,362 and 592,respectively,and173 OTUs were shared by these four groups.The Alpha diversity order of the bacterial from high to low was:group 4>group 2>group 3>group 1.The richness and diversity of microflora were higher in group 4,indicating that compensatory growth could effectively increase the richness and diversity of the microbial community in the aquaculture water.Beta diversity analysis showed that the microbial composition of group 1 and group 2 were relatively close,and different from group 3 and group 4 with PCA analysis and UPGMA cluster analysis.The abundance analysis at genus level showed that the most dominant flora of group 1 was Georgenia（20.2%）,followed by Hydrogenophaga（13.5%）and Pseudomonas（13.2%）.In group 2,the highest abundance was Pseudomonas（39%）,followed by Georgenia（9.1%）and Brevundimonas（7.0%）.In group 3,the highest abundance was Brevundimonas（38.4%）,followed by Microbacterium（5.7%）and Caulobacter（5.7%）.In group 4,the highest abundance was Alishewanella（21.0%）,followed by Pseudomonas（15.5%）and Exiguobacterium（6.8%）.The the proportion of pathogenic bacteria in group 3 and group 4 were reduced.It showed that the biofloc technology could optimize the composition of the microbial community in the aquaculture water of Litopenaeus vannamei.3.The number and species of algae in different groups were counted by the plankton counting frame（0.1ml）using the Olympus BX41 microscope.The results showed that the dominant algae in the four groups were chlorophyta,cyanophyta and bacillariophyta.The beneficial algae such as Euglena and Phacus in group 2,and Cosmarium,Coelastrum and Oocystis were increased in group 3 and 4 respectively.The harmful algae such as Pseudanabaena and Raphidiopsis were reduced in group2,3,4,indicating that biofloc effectively improve the species of phytoplankton and reduce the pollution of aquaculture water.Chlorophyll a content was determined by thermal ethanol method.The results showed that at the 4^thweek,the contents of Chl.a in group 3,group 4 were significantly higher than that in the control group（P<0.05）.These results indicated that probiotics and compensation growth could increase the content of chlorophyll a.4.The concentration of ammonia nitrogen and nitrite nitrogen showed a increasing trend in group 1,and increasing at first and then decreasing trend in group2,3 and 4.At the 4^thweek,the contents of ammonia nitrogen and nitrite nitrogen in groups 2,3 and 4 were significantly lower than these in group 1（P<0.05）.It showed that biofloc technology reduced the concentration of ammonia nitrogen and nitrite nitrogen in aquaculture water.5.The weight gain rate（WGR）of group 2 was significantly higher than the other three groups（P<0.05）,and the feed conversion rate（FCR）of group 4 was significantly higher than three other groups（P<0.05）,indicating that biofloc technology could promote the shrimp growth,and the compensatory growth could increase the feed conversion rate.The results showed the biofloc technology based on compensatory growth could effectively increase the richness and diversity of microflora,improve the species of microflora and phytoplankton,and increase the content of chlorophyll a to reduce the concentration of ammonia nitrogen and nitrite nitrogen in the aquaculture water.The biofloc technology could promote the shrimp growth,and the compensatory growth could effectively increase the feed conversion rate.