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Assessing the Effects of Fluoxetine on the Gut Microbiome of Fathead Minnow



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The understanding and importance of incorporating the microbiome as a measurable indicator of toxicity has only recently come about in the scientific discipline of ecotoxicology. The microbiome, specifically the gut microbiome, plays a critical role in host homeostasis where it can communicate, interact and influence the nervous, immune and gastrointestinal systems as well as the brain. The microbiome holds importance in ecotoxicology studies as microbiota can detoxify and activate toxicants and, if perturbed by contaminants, influence the host response to these compounds. Given some gut florae can influence neurochemicals, synthesize biogenic amines and express neurotransmitter:sodium symporters, it is valuable to understand how antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs), can affect the gut microbiome. SSRIs are known contaminates found in aquatic environments, which has led to an abundance of ecotoxicology studies covering behavior, reproduction, and developmental research on aquatic organisms. However, no study has yet been identified assessing the gut microbial response to SSRIs in the field of ecotoxicology such as within fish. A preliminary study was first conducted to identify if fluoxetine, a common SSRI, can impede growth of bacterial cells cultured from the gut of fathead minnow (Pimephales promelas). This was an in vitro study, where bacterial cells were inoculated with a serial dilution ranging from 0.015 to 128 µg/mL of fluoxetine. At nominal fluoxetine concentrations of 32, 64 and 128 µg/mL, growth of bacterial cells was found to indeed be inhibited. With preliminary results identifying inhibition of growth due to fluoxetine exposure, an in vivo study followed where fathead minnows were exposed to three concentrations of fluoxetine or a control. Nominal concentrations consisted of 0.01, 10 and 100 µg/L. After a 28 day exposure to aqueous fluoxetine, fish were euthanized, intestines were extracted and DNA extraction, amplification, purification and sequencing was conducted on the 16S rRNA gene to identify the abundance and diversity of the gut microbiome. Results indicated that the highest exposed group held a significantly altered gut microbiome compared to the control, low and middle groups. It was also found that male and female fish hold distinct gut microbiomes. These findings are the first to identify that SSRIs can influence the gut microbiome of fish, although at a concentration much higher than known environmental concentrations. While the results are inconclusive at lower concentrations more commonly measured in the aquatic environment, insight still may be gained into how potential mixtures and continuous persistence of SSRIs may impact the gut microbiome of fish long-term. This research can also help interpret how such concentrations of fluoxetine may influence the gut microbiome of other organisms using the cross-species extrapolation hypothesis to predict similar effects on evolutionarily conserved molecular targets. Possible next steps would be to perform a mixed-omics approach to accurately understand not only “who is there” but “what they are doing”; essentially, how the gut microbiota is functioning and interacting with its host. These methods could provide a more in-depth examination into how perturbations of the gut microbiome may be influencing host homeostasis.



Gut microbiome, Environmental Toxicology, Wastewater, Fish, Pharmaceuticals



Master of Science (M.Sc.)


Toxicology Centre




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