Nutrient regulation of endocrine function in fish

Abstract

Hormones play a central role in the regulation of growth and nutrient utilization in fish. Consequently, fish endocrine systems are sensitive to alterations in nutrient intake. Procedures routinely employed in the development of diets and feeding protocols for cultured fish have pronounced effects on endocrine systems. We review the evidence that alterations in ration level (including food restriction and food deprivation), diet composition, photoperiod, and feeding time influence the most intensively-studied fish metabolic hormones: thyroid hormones, pancreatic hormones, and hormones of the growth hormone–insulin-like growth factor axis. Whereas effects of these dietary manipulations on total circulating hormone levels are commonly examined, nutrient intake may also influence hormone transport in blood, activation in peripheral tissues, receptor binding, and neuroendocrine pathways regulating hormone secretion. Information on the cellular and molecular mechanisms through which nutrients influence endocrine systems is still needed. Significant new information about the regulation of endocrine function can be derived from nutritional studies currently employed in aquaculture for the development of diets. Additional information on the influence of nutrients on endocrine function is essential for the design and interpretation of hormone supplementation studies, and should eventually allow development of feeding strategies which promote anabolic hormone production.