| Bighead carp(Hypophthalmichthys nobilis)is one of the most widely cultured freshwater species in China and a significant species used in water purification fisheries due to its filter-feeding properties.At present,the implementation of the Yangtze River’s ban on catching,combined with the increasing demand for green aquaculture,has continued to draw attention to pond aquaculture in the mode of nesting or polyculture.However,current research into the correlation between physical and chemical indicators of water bodies and plankton,as well as the metabolism of cultivated fish under conventional nesting mode,is still limited.In this study,water samples from two ponds that tilapia and common carp polycultured bighead carp were examined and analyzed for physicochemical indices and plankton community structure for eight sampling periods,respectively,from May 2019 to September 2019.The characteristics of the intestinal microbiome of bighead carp from two different reared patterns were also compared using Illumina Hi Seq sequencing of bacterial16 S r RNA.In addition,SNP molecular markers were developed based on transcriptome sequences,and genetic analyses were performed on the collected bighead carp samples.By observing the intestinal microbial diversity and its changes of bighead carp,the relationship with the physicochemical indicators and biological communities of the water body was investigated to provide basic data for understanding the feeding choice or adaptations of bighead carp in the polyculture mode.1.Water samples were examined for physicochemical indices and plankton observations and analyses in two ponds for tilapia and common carp polyculture with bighead carp at eight sample points from May to September 2019(May 15,May 30,June 20,July 11,July 23,August 8,August 21,and September 12).Throughout the culture period,the average water temperature of the two ponds was 29.3±4.5 ℃,and the p H value was 7.33-7.87,total nitrogen,dissolved nitrogen,and ammonia nitrogen both showed an increasing trend,while nitrite nitrogen was at a lower concentration;total phosphorous,dissolved phosphorous,and phosphate were all showed an increasing and then decreasing trend.The results of the plankton test revealed that there were 8 phyla and 77 genera of phytoplankton,mostly in the Chlorophyta and Cyanophyta,and 5 classes and 72 species of zooplankton,with protozoa and rotifers as the dominant species.The population structure of plankton had apparent characteristics of temporal shifts at different culture stages,according to principal component analysis(PCA)and heat map analysis based on plankton abundance values.Combining the redundancy analysis(RDA)of water body physicochemical influences on the overall changes of phytoplankton,we discovered that nitrite and total nitrogen concentrations had significant effects on phytoplankton abundance(P <0.05),while water temperature,p H and nitrite concentration had significant effects on zooplankton abundance(P <0.05).The correlation analysis between species abundance and physicochemical index further demonstrated significant(P <0.05)or highly significant(P <0.01)linear associations between the abundance of certain planktonic organisms and several physiochemical indicators.The findings show that during the main aquaculture period in the pond intercropping mode,the plankton community structure of the water body undergoes obvious sequential changes and is affected by the physical and chemical indicators of the water body.2.A genetic analysis of different experimental bighead carps based on SNPs was carried out,aimed to prepare the ground for the forward research on intestinal microbes.A total of37 SNP loci were developed based on bighead carp transcriptome data,and their allele frequencies in 24 experimental bighead carps were analyzed using PCA,which revealed there were no significant genetic differences among the bighead carp samples collected from each experimental group.These results indicates that variations in genetic background had no impact on the gut microbial community structure of the experimental bighead carp.3.Illumina Hi Seq sequencing of bacterial 16 S r RNA for four sampling sites(May 15,June 20,July 23,and August 21)was used to compare the characteristics of changes in the intestinal microbiome of bighead carps under two different reared patterns.The results indicated that 779,563 quality-filtered sequences and 8,870 ASVs from 24 samples were obtained,and 35 phyla were identified that dominated by Proteobacteria,Firmicutes,Fusobacteria and Cyanobacteria.According to alpha-and beta-diversity measurements,the bacterial communities of different samples were diverse,and Chao1 richness and Pielou’s evenness were significantly(P <0.05)lower in the T2 B and T4 B groups than others that related to processing operations including the refilling of freshwater during the culture process.PCo A and NMDS analyses showed that the intestinal bacterial communities of groups T1 A,T1B,T2 A and T2 B were significant different from the other samples,and there were variations in the community structure of fish intestinal microorganisms at different stages of culture,which could be related to factors like fish growth and production operations. |
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