NUTRIENT REGULATION OF ENDOCRINE FUNCTION IN FISH

Hormones play a central role in the regulation of growth and nutrient utilization in fish. Consequently, fish endocrine systems are sensitiv e 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 a lterations in ration level (including food restriction and food depriv ation), diet composition, photoperiod, and feeding time influence the most intensively-studied fish metabolic hormones: thyroid hormones, pa ncreatic hormones, and hormones of the growth hormone-insulin-like gro wth factor axis. Whereas effects of these dietary manipulations on tot al circulating hormone levels are commonly examined, nutrient intake m ay also influence hormone transport in blood, activation in peripheral tissues, receptor binding, and neuroendocrine pathways regulating hor mone secretion. Information on the cellular and molecular mechanisms t hrough which nutrients influence endocrine systems is still needed. Si gnificant new information about the regulation of endocrine function c an be derived from nutritional studies currently employed in aquacultu re for the development of diets. Additional information on the influen ce of nutrients on endocrine function is essential for the design and interpretation of hormone supplementation studies, and should eventual ly allow development of feeding strategies which promote anabolic horm one production. (C) 1998 Elsevier Science B.V.