Study On The Gut Microbial Community Structure Of Bighead Carp And Its Effect On The Quality Of Its Host Under Three Kinds Of Culture Environment

Different water quality and habitat have great influence on the growth and development of fish.Water quality is closely related to water surface size,climate,environmental ecology,elevation,geographical location and aquaculture conditions.These factors have obvious effects on fish growth,disease resistance,distribution and abundance of gut microbiomes,nutritional components and metabolic process.At present,systematic studies on the relationship between gut microbiomes and their quality and metabolic regulation in different habitats are rare.In order to understand the relationship between gut microbiomes and intestinal metabolites and the quality of bighead carp in different habitats,three typical aquaculture waters,i.e.common culture pond?NC?,Lake?PYL?and cold water reservoir?XHK?,were studied in this study.Firstly,the effects of water quality and plankton spatial and temporal patterns in three different habitats on bighead carp culture were investigated.It was found that there were significant differences in water quality and plankton community structure among the three habitats?p < 0.05?.Secondly,the muscle nutrients and volatile flavor compounds of bighead carp in three habitats were compared and analyzed.The results showed that there were significant differences in the contents of crude protein,crude fat,amino acid,SFA,PUFA,MUFA and volatile flavor compounds of bighead carp muscle in different habitats?p < 0.05?.In order to further analyze the mechanism of different environmental impacts on the quality of Bighead carp,this study combined the analysis of intestinal microbial community structure and metabolites changes,and used multi-group combined analysis to analyze the correlation between differential microorganisms and metabolites.Several candidate microorganisms?Clostridium_sensu_stricto₁,Nocardioides,Fluviicola?were screened out.These microorganisms and lipids were identified.The metabolic pathways of acid and lipid are closely related.This study not only lays a theoretical foundation for revealing the mechanism of quality change of Bighead carp,but also has great practical significance and application value forimproving the quality and economic added value of freshwater cultured bighead carp in China.The main results of this study are as follows:1.Water Quality Monitoring and Plankton Spatial-temporal Patterns in three culture environmentThe main monitoring indicators in this experiment are temperature,dissolved oxygen?DO?,p H,ammonia nitrogen?NH4+-N?,nitrate nitrogen?NO3+-N?and transparency.Generally speaking,the changes of temperature,p H and nitrate nitrogen showed the same seasonal trend,but the dissolved oxygen content in NC aquaculture waters fluctuated greatly and was generally higher than that in PYL aquaculture waters and XHK aquaculture waters.The nitrate and ammonia nitrogen content in NC aquaculture waters were also higher than that in PYL and XHK aquaculture waters.The average annual water temperature of XHK aquaculture waters was the lowest among the three bighead fish aquaculture waters.The results of phytoplankton research show that the biomass of phytoplankton in NC aquaculture waters is significantly higher than that of PYL and XHK,but the number of species in NC aquaculture waters is lower than that in PYL aquaculture waters and higher than that in XHK aquaculture waters.The biomass of phytoplankton in XHK waters is the smallest in the three aquaculture waters,and the number of species is the lowest.NMDS analysis showed that there were significant differences in zooplankton community in spring and summer,followed by autumn,and no significant differences in community structure in winter.RDA results showed that the difference of phytoplankton community structure was positively correlated with water temperature,p H and Cyanophyta biomass.Zooplankton studies have found that the diversity of zooplankton in PYL waters is the best,followed by NC waters and the lowest in XHK waters,which may be closely related to the unique water quality environment in XHK waters.2.Comparative Analysis of Nutritional Components and Volatile Flavor Substances in Muscles of Bighead Carp in three culture environmentThe results showed that the nutrient composition of bighead carp meat was greatly affected by different nutrient types of water.Compared with NC and pyl,the content of water and ash in muscle of bighead carp in XHk waters was higher,and the content of crude protein and fat was lower.The nutritional evaluation of bighead carp in XHK waters was better than that in NC and PYL waters,and the contents of DHA and EPA reached 18.96%.48 volatile flavor compounds were identified from three groups of Bighead samples,including Nonformaldehyde,octyl aldehyde and 1-octyl-3-alcohol with mushroom flavor and earthy flavor.Eugenol with sweet and fruity aroma is the main volatile flavor substance.The content of Bighead fishy substance in XHK waters is lower than that in NC and PYL waters,and the content of fresh flavor is higher than that of NC and PYL.Histological structure analysis showed that bighead carp in XHK group had finer meat and better water holding capacity,followed by bighead carp in PYL group,which had tender taste,and bighead carp in NC group had tighter muscle and harder taste.3.Analysis of gut microbial composition of Bighead CarpIn this study,a total of 1,030,903 clean tags were extracted from 34 intestinal samples of bighead carp in three different habitats.The average clean tags of each sample were 30,320,with an average length of 420.76-435.66 bp.The gut microbial composition of bighead carp in the three habitats was significantly different from each other.The group_XHK sample had the highest microbial diversity?Kruskal-Wallis,p< 0.05?,while the NC sample had the lowest microbial diversity?Kruskal-Wallis,p <0.05?.At the phylum level,the most abundant intestinal flora of the three habitats are Proteobacteria?30.98%?,Fusobacterium?22.87%?,Bacteroidetes?14.66%?,Actinobacteria?14.56%?and Firmicutes?6.00%?five phylums;at genus level,Vibrio?6.46%? and Llibacteroides?3.74%?,Aeromonas?2.54%?,Clostridium_sensu_stricto₁?2.25%?,and Gemmatimonas?1.31%?were the dominant genera with the highest relative abundance.Statistical analysis at the generic level showed that the highest relative abundance genera were Ambiguous_taxa and Gemmatimonas ? Nocardioides?Kruskal-Wallis,p<0.01?in the gut tract of bighead carp in Group_XHK group.The relative abundance of Aeromonas and Vivrio in the gut of bighead carp in Group_PYL group was significantly higher than that in the other two habitats?Kruskal-Wallis,p < 0.01?.The results show that: 32 general gut microorganisms i.e.Candidatus_Solibacter and Sphingomonas of bighead carp consist of strong positive correlation modules,while seven genera such as Macellibacteroides and Lostridium_sensu_stricto₁ are negative correlation modules.4.Metabonomics and Conjoint AnalysisIn this study,the metabolites of intestinal contents were analyzed by GC-MS and LC-MS methods,and 568 metabolites with significant differences were screened.The differential metabolites screened by LC-MS were mainly concentrated in glycerol ester metabolism,linoleic acid metabolism,m TOR signaling pathway,alpha-linoleic acid and beta-linolenic acid metabolism.The differential metabolites screened by GC-MS were mainly concentrated in glutathione metabolism,ABC transporters,glycerol phospholipid metabolism and beta-alanine metabolism,which well explained the molecular differential mechanism of bighead carp metabolism in different habitats.The most significant environmental factors affecting the structure of intestinal microbial community were water temperature?WT?and dissolved oxygen?DO??p <0.05?.The three habitats with different water quality shaped significantly different microbial structures?p < 0.05?.Clostridium_sensu_stricto₁,Nocardioides ?uncultured_Acidimicrobineae_bacterium were significantly correlated with several important metabolites in lipid metabolism pathway?| R | > 0.86,p < 0.01?,suggesting that lipid metabolism was regulated by gut microbiomes in three different habitats to affect the quality of Bighead carp.Deeply,molecular mechanisms need to be further studied.