Endocrine regulation of appetite and growth in Atlantic cod (Gadus morhua)

Xu, Meiyu (2009) Endocrine regulation of appetite and growth in Atlantic cod (Gadus morhua). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Atlantic cod, Gadus morhua, is an important commercial fisheries species in many North Atlantic countries. Due to the recent decline in cod populations worldwide, Atlantic cod has become an emerging species in aquaculture in Canada, in particular New Brunswick, and Newfoundland and Labrador. The well-developed resistance to long-term starvation also makes cod a good model for the study of growth- and appetite-related hormones under both short-and long-term nutritional changes. The endocrinal regulation of food intake and energy homeostasis involves a two-way communication of hormones existing in central nervous system and several peripheral organs. I aimed to identify and characterizing genes coding for two growth-related factors (PACAP and SS), as well as one central (OX) and two peripheral (ghrelin and GRP) appetite-related factors in Atlantic cod. Multiple alignments and phylogenetic analyses show that the amino acid sequences all 5 peptides appear relatively conserved among fish, at least among teleosts. The typical expression patterns reflect their functional regions and are highly similar to those of other teleosts reported so far, with high forebrain expression levels for brain peptides and high stomach expression levels for gut peptides. For all the peptides in the present study, an early appearance in development probably indicates a crucial role in development. The apparent differences of expression for PPSS 1, OX and NPY before and after first larval feeding suggest that growth and appetite in fish are already under strict endocrine regulation at very early stages of life. The different expression patterns displayed by PPSS 1 and PRP/PACAP during fasting and re-feeding indicate that they might have distinct functions in the regulation of feeding and metabolism of Atlantic cod. OX and NPY both display periprandial changes and appear to be more affected by re-feeding than a long fasting period, while an increase in CART expression was induced during long-term food deprivation. Ghrelin displayed periprandial changes in expression but was not affected by fasting, while GRP did not display periprandial changes but was affected by food ration. One month exposure to different photoperiods did not affect food intake, body length or growth condition factors in juvenile cod. No overall orexigenic or anorexigenic tendency is shown in juvenile cod, though hypothalamic expressions of both NPY, an appetite stimulator, and CART, a feeding inhibitor, increase in cod exposed to complete darkness compared to fish in constant light. QPCR showed no significant effects of photoperiod on the expression levels of gut ghrelin and GRP. In general, the interaction displayed in Atlantic cod between brain and gut peptites with appetite and nutritional status may help further understanding of the endocrinal control of appetite and the effects of environmental factors, such as photoperiods, in teleosts.

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