The influence of nutritional status and environmental factors on growth, feeding behaviour and appetite-related peptide transcript expression in Atlantic cod (Gadus morhua)

Tuziak, Sarah (2016) The influence of nutritional status and environmental factors on growth, feeding behaviour and appetite-related peptide transcript expression in Atlantic cod (Gadus morhua). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Appetite regulation and energy homeostasis are critical processes for vertebrate survival that are regulated by neuroendocrine mechanisms. Understanding how appetiteregulating hormones are influenced by intrinsic and extrinsic cues is essential for the comprehension of how vertebrates maintain an appropriate energy balance. This thesis focuses on some important appetite regulators [melanin-concentrating hormone (MCH), orexin, neuropeptide Y (NPY), gonadotrophin-releasing hormone (GnRH) and cocaineand amphetamine-regulated transcript (CART)] in a commercially important fish species, Atlantic cod (Gadus morhua). To begin my analyses of these important appetiteregulating hormones in cod, I identified for the first time cDNA sequences for MCH and GnRH mRNAs, while orexin, NPY and CART transcripts were previously isolated in cod. MCH and GnRH hormones were shown to be expressed in regions of the brain and peripheral tissues (i.e. gastrointestinal tract) related to food intake regulation. MCH, but not GnRHs, transcript expression was higher in fed compared with fasted fish, indicating that MCH may play an important role in appetite regulation in cod. Then, I examined how diet (i.e. plant-based feed, Camelina sativa) and environment (i.e. background colour) influence feeding behaviour and appetite-related peptide transcript expression. Camelina meal-supplemented feed reduced food intake and growth, and increased orexigenic peptide mRNA expression (i.e. MCH, orexin and NPY), but did not affect CART expression, suggesting fish are still “hungry” and that MCH, orexin and NPY peptides could be involved in other feeding behaviours and metabolic processes, such as nutrient sensing and food searching behaviour. Finally, I addressed the effects of background colour and fasting on Atlantic cod feeding and swimming behaviour, as well as appetiterelated transcript expression. Atlantic cod subjected to fasting and different background colours displayed reduced locomotion. Furthermore, a decrease in MCH and orexin mRNA expressions in fasted fish was observed and might possibly be correlated to a reduction in locomotion and feeding activity rather than indicative of anorexigenic effects. Finally, fasted fish had paler skin colour compared to fed fish in white backgrounds. These results suggest that MCH, orexin and NPY may play important roles in various appetite-related behaviours and physiological processes, whereas CART and GnRH may not have significant roles in food intake regulation in Atlantic cod. Understanding feeding regulation and how various cues can influence food intake is fundamental for the development of sustainable aquaculture industries.

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