The effect of nutritional status on goldfish (Carassius auratus) gut microbiota composition and energy homeostasis

Butt, Robyn Lisa (2019) The effect of nutritional status on goldfish (Carassius auratus) gut microbiota composition and energy homeostasis. Masters thesis, Memorial University of Newfoundland.

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Abstract

The microorganisms within the intestinal tract (termed gut microbiota) have been shown to interact with the gut-brain axis, a bidirectional communication system between the gut and the brain mediated by hormonal, immune, and neural signals. Through these interactions, the microbiota might affect behaviours, including feeding behaviour, digestive/absorptive processes (e.g., by modulating intestinal motility and the intestinal barrier), metabolism, with repercussions on the energy homeostasis and health of the host. To date, research in this field has mostly focused on mammals. Studies on nonmammalian models such as fish may provide novel insights into the specific mechanisms involved in the microbiota-brain-gut axis. The goldfish gut microbiota was initially analyzed in various regions of the gut (foregut, midgut and hindgut), with similarities found among gut regions and fish samples. The effects of two and four weeks of fasting and a synbiotic-based diet on the goldfish midgut microbiota was then analyzed. Fasting resulted in no significant differences in the midgut microbiome diversity in goldfish. There were significant differences between two and four-week fasted groups with regards to the abundance of specific bacterial taxa (species composition). The synbiotic diet induced a decrease in the microbiome biodiversity in comparison to the control diet, and significant changes in the species composition. Goldfish fed the synbiotic diet had a significant increase in food consumption compared to fish fed the control diet. I examined the effects of fasting and a synbiotic diet on the expression of appetite regulators. Fasting had no effects on the mRNA expressions of brain orexin and CART1 or foregut GLP-1, but decreased brain CART2 and foregut CCK, and PYY, which was expected, as these are anorexigenic hormones. The synbiotic diet had no effect on relative brain mRNA expression of brain orexin, CART1 and CART2 or foregut CCK and GLP-1 but increased mRNA foregut expression for PYY. Overall, this study provides new insights into the effects of nutritional status on the goldfish gut microbiota and energy homeostasis, and suggests that alterations of the gut microbiota due to changes in nutrition may regulate the central and peripheral expression of genes related to appetite and digestion.

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