show Abstracthide AbstractThe composition of the gut microbiome is known to be a significant factor in the health of a variety of hosts. Therefore, it is then important to ascertain how readily the gut microbiome can be significantly altered. To this end, the role of changing diet on the gut microbiome of the Pacific oyster (Crassostrea gigas) was assessed. Over the course of 12 weeks isolated individual oysters were fed either a control diet of Tetraselmis algae, or a treatment diet which shifted in composition every 4 weeks. Weekly fecal samples from all oysters were taken to characterize their gut microbiota. Concurrent weekly sampling of the algal feed cultures was performed to assess the effect of algal microbiomes, independent of the algal type, on the microbiomes observed in the oyster fecal samples. Changing the algal feed was found to be significant in changing the gut microbiome, over a time scale of weeks, between control and treatment groups of oysters. No significant differences between individual microbiomes were found within control and treatment groups. This suggests the gut microbiome of the Pacific oyster can be quickly and reproducibly manipulated.