Gut bacteria play important physiological roles in their animal hosts, influencing metabolic processes either by altering host gene expression or by directly breaking down digested food items. Because gut microbes play a significant role in energy extraction, it is important to assess what factors influence the gut microbial community within an animal.  Previous literature has shown that host taxonomy shapes gut microbes in the mammalian gut indicating co-evolution between microbes and their hosts. Mammalian gut communities were also influenced by diet. To date, it is unclear whether such relationships hold in other organisms, such as fish. In this study, we compiled 16S rRNA bacterial sequences from fish gut associates that had been deposited in GenBank as well as those that have been isolated in our lab. These data allowed us to investigate the phylogenetic relationships among fish gut bacteria. We then explored what factors shape fish gut communities, focusing on the fish hosts’ taxonomy, environment (i.e. freshwater, marine, farm-reared or wild caught) and diet. Through this study, we aim to explore what factors influence the distribution of microbes in the guts of fish, which may have important implications for the roles of bacteria in facilitating adaptations to different environments.   
Results/Conclusions

The taxonomy of the fish host appears to shape the microbes that are found in its gut. This is also evident from the difference in dominant gut microbes between fish and mammalian hosts. Fish libraries are dominated by Proteobacteria, while previous studies have indicated that this is not the case for mammalian species. The gut flora of fish are shaped by a variety of environmental factors that synergistically influence which bacteria are able to become established in their gut environment.