Regulation of nutrient intake and energy balance in salmon

There is a correlation between growth, adiposity and early maturity in salmonids. One strategy to avoid early maturity may be to favor muscle growth over fat accumulation. The present article discusses the regulation of food intake and fat storage under conditions of either relative over-abundance or insufficiency of energy intake in salmon. In a series of experiments with chinook salmon of equal size, food intake of fat fish was significantly less than in their lean counterparts. Furthermore, when fat and lean fish were pooled and given access to the same diet, whole body fat levels converged, suggesting a robust mechanism for regulating body fat stores. Growth of the initially fat fish was impaired relative to the initially lean fish. In separate experiments, when chinook and coho salmon were deprived of food, hypothalamic expression of neuropeptide Y (NPY)-like mRNA increased significantly compared to fed controls. Increased hypothalamic NPY mRNA and NPY secretion have been shown to be central elements of energy balance regulation in mammals. The increase in hypothalamic NPY-like gene expression in a teleost may reflect the primitive evolution a central mechanism to regulate energy intake and expenditure that has been elucidated in mammals.