Gut-brain axis and the neuroendocrine regulation of energy balance, growth and reproduction in fish

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The focus of my research is on how hormones (endocrine factors) produced from the brain and gut regulate food intake, growth and reproduction in fish. Food intake is mainly regulated by endocrine factors produced from the brain and gut, while growth and reproduction are regulated by factors produced mainly from the brain, pituitary and gonads (testis/ovary). Using goldfish, a well-characterized model used to study hormones, I have previously shown that two gut-brain peptides ghrelin and galanin stimulates food intake and secretion of growth hormone (GH; regulates growth) and luteinizing hormone (LH; regulates reproduction) secretion in fish. I hypothesize that (i) the regulation of feeding, growth and reproduction are interlinked by gut-brain endocrine factors and (ii) the appetite regulatory peptides act directly on the gonads to regulate reproduction. The overall objective of this proposal is to study how certain endocrine factors integrate food intake, growth and reproduction in fish. During the term of this grant, I will expand my studies on the biological actions of ghrelin and galanin and identify the structure and functions of two other appetite regulatory factors, galanin like peptide (GALP) and peptide YY (PYY) in goldfish. Endocrine factors (eg: GALP, PYY) will be administered into the brain or into the stomach cavity and food intake and GH and LH levels in blood will be determined. Presence of ghrelin, galanin, GALP and PYY in the gonads of goldfish will be determined and their direct effects on gonads will be studied. I also propose to use zebrafish that genetically lack ghrelin to further characterize the appetite regulatory, growth and reproductive functions of ghrelin in fish. Collectively, the results of the fundamental studies outlined in this proposal (i) are expected to provide new information that will improve our knowledge about the hormonal regulation of food intake, growth and reproduction in fish and (ii) could be beneficial in aquaculture to promote growth and reproduction of cultured fish.