Water Pollution Shapes The Commensal Microbial Community Structure In Fishes

Water pollution is an important environmental problem all over the world,which can destroy the diversity of aquatic animals such as fish.The host commensal microbial balance plays a vital role on many aspects,such as nutrient metabolism and disease defense.The disorder of microbial commensal may disable some functions of host immunity,aggravate the development of disease and even leading to disease.Studies have shown that water pollution can change the composition and function of microbial communities in free water and sediments,and the gut microbial communities of fish living in waters of different environmental microorganism compositions differ.However,the effects of water pollution on fish commensal microorganisms have not been extensively studied.In this paper,we aim to investigate the effects of water pollution on the composition of commensal microbial communities in Carassius auratus.Xiaoqing River is an important urban sewage and landscape river channel in Jinan City.It originates from Mulizhuang and flows to theurban of Jinan.It is out of Jinan in Zhangqiu and enters the sea in Weifang.The Xiaoqing River originated in Jinan and immediately became contaminated by the city.It was decided that the basin was a good example for conducting pollution ecology research.In this study,fish samples(intestine and surface)and environmental samples(free water and sediments)were collected from the headwater section and the urban section of the Xiaoqing River in Jinan City.We characterized the microbial composition of free water(n = 3),sediment(n = 3),intestinal(n = 10),and surface(n = 10)in the headwater section and intestinal(n = 10),surface(n = 10)in urban section by high-throughput sequencing using 16 S r RNA marker.The physical and chemical properties of the free water were also detected in the two sections.The analysis of water quality and fish diversity indicated that COD,TN,NH3-N and BOD5 in the headwater section were significantly lower than those in the urban section(Student’s t test,p < 0.001),and p H value of the headwater section was significantly higher than that of the urban section(Student’s t-test,p < 0.01);the Shannon index of fish was significantly higher than that of the urban section.The shannon diversity analysis of microbial community revealed no significant change in the intestinal and surface microbial community between Headwater and Urban(Student’s t-test,p > 0.05);respectively,the intestinal and surface microbial community compositions were significantly different(Wilcoxon test,p < 0.05)between Headwater and Urban;the probiotics such as Proteobacteria,Lactobacillus and Bacillus in the intestine of the urban section were significantly reduced(Student’s t-test,p < 0.05),among which Lactobacillus was also the core microbiota of the intestine,while the disease-associated microbiota such as Staphylococcus was significantly increased in the surface of the urban section(Student’s t-test,p < 0.05);the free water and sediment microbial community compositions between Headwater and Urban were no significant difference(Wilcoxon test,p > 0.05);COD and p H were significantly correlated with the composition of the intestinal and surface microbial community between Headwater and Urban.The results indicate that elevated COD and decreased p H in water may lead to the development of microbial microbial communities in a direction that is not beneficial to the health of Carassius auratus.This study described the effects of water pollution on fish health from the perspective of microbiota,studies the response of fish commensal microbiota to the changes of water pollution,and provides theoretical guidance for fish disease control,population conservation,and community diversity maintenance.