SILVERSTEIN, JT; USDA-ARS-NCCCWA: Neurohormonal regulation of feeding in fish

There is extraordinary diversity in life histories of fish with regard to feeding, for example the prolonged periods of fasting in salmon and lamprey contrasted with periods of extreme prespawning consumption in some teleosts such as scorpaenids. In addition to life history programming, feed intake is affected by the animals� external and internal environments. Temperature, photoperiod, and background coloration are a few of the external environmental elements that influence feed intake. The levels of energy storage, and degree of stress are just two of the internal conditions that influence feeding rate. While it is generally recognized that feeding centers in the hypothalamus coordinate the multiplicity of signals into an appropriate behavior, the hormonal and neuroendocrine systems inform the feeding centers. The accumulating work by several research groups using intraventricular injections into the fish brain have shown similarities with the findings in mammals regarding the roles of neuropeptides such as neuropeptide Y, CART and CRH, however metabolic hormones such as insulin and glucagons family peptides have not been shown to have a clear physiological effect on feed intake. Other studies on environmental factors through manipulation of temperature, photoperiod, background coloration and feed availability have demonstrated effects both on feeding and on various hormones such as growth hormone, IGF-1, thyroid hormones and MSH. However, the link between neuroendocrine and hormonal fluxes and effects on feed intake remain mostly correlative and circumstantial. Continued investigations of peptide and receptor abundance, gene expression studies, and use of agents such as antagonists, antibodies and antisense molecules to block specific ligand actions are necessary to clarify hormonal and neuroendocrine effects on feeding and their physiological relevance.