DISSERTATION RESEARCH: Is richer always better? Testing the biotic resistance hypothesis in ornamental fish microbiomes

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The sum of microorganisms living on and in a host is called the "microbiome". A host's microbiome often has more cells and functions than the host itself, and plays important roles in nutrition, health and disease. Antibiotic treatment disrupts microbiomes in mice and humans and increases the likelihood of bacterial infections after treatment. Fish depend on their microbiome and are often treated with antibiotics in commercial settings, particularly along ornamental trade routes where suppliers must deliver a disease-free product to retail pet shops. This study will test if antibiotics have the unintended consequence of disturbing fish microbiomes during shipment, thereby reducing disease resistance after fish have arrived in retail store tanks. The researchers will collaborate with the Woods Hole Partnership in Education Program to involve underrepresented groups in the laboratory research. Additionally, the researchers will continue ongoing collaborations with ornamental fish industry members, engaging the private sector in science-based solutions to disease. This research will provide valuable insight into the role microbiomes play in aquaculture diseases and potential probiotic treatments, and contribute to the advancement of science-based solutions to aquaculture development. A reduction in biotic resistance, or the ability to protect the host from colonization andproliferation of external pathogens, often accompanies antibiotic treatments. The first aim of this research is to assess the influence of antibiotics on disease resistance in fish microbiomes, using aquarium-based experiments in the laboratory. Ornamental fish shipments with and without the use of antibiotics will be simulated, followed by a spike of a known fish pathogen. Biotic resistance will be measured by mortality, and the relative abundance of the spiked pathogen within fish microbiomes. In humans and mouse models, re-inoculation after antibiotic treatment with a high-richness microbial community restores biotic resistance. The second objective of this research will be to test a range of bacterial inoculates for their ability to restore biotic resistance in fish microbiomes after antibiotic treatment. These inoculates will vary in their richness and composition, and biotic resistance will be assessed as above, alongside resulting microbiome richness. The researchers will test the hypothesis that a low-richness recovery inoculum of probiotic species representing a variety of disease resistance mechanisms will provide the strongest possible microbiome-mediated biotic resistance.