Growth hormone axis as marker of nutritional status and growth performancein fish

The endocrine control of growth and metabolism is interrelated and many of the endocrine factors involved in the regulation of lipid and protein metab olism are also involved in nutrient utilization, immune system function and somatic growth. All these processes are impaired in catabolic states induc ed by fasting, protein deprivation and chronic liver diseases as a response to the consequential changes in the endocrine system. In this regard, it m ust be noted that concentrations of circulating metabolites may be quite di fferent depending on the catabolic state. However, in all the metabolic dis orders that shared an increased catabolism/anabolism balance, plasma insuli n levels are depressed, whereas those of GH are elevated. This hypersomatot ropism, linked to growth retardation, is accompanied by a reduction of plas ma IGF-I concentration, which reflects some refractoriness of liver to the anabolic action of GH. Changes in GH availability and liver GH-responsivene ss can also be established as a function of age, fish species, and environm ental factors (photoperiod and temperature). In the present work, the regul ation and mode of GH action is discussed in order to provide a useful tool to assess the nutritional status and growth performance of cultured fish. ( C) 1999 Elsevier Science B.V. All rights reserved.