Ghrelin is involved in voluntary anorexia in Atlantic salmon raised at elevated sea temperatures

Due to global and local climate changes, farmed salmon may experience periods of elevated sea temperatures. An experiment was conducted to examine endocrine and dietary effects of high sea temperatures in adult (2.0 kg) and sexually immature Atlantic salmon, Salmo salar L Groups of salmon were exposed to 19 degrees C while others were kept as controls at 14 degrees C. The experiment lasted for 56 days, and fish were given iso-nitrogenous diets with either a normal (335 g kg(-1); L34) or a lower lipid level (298 g kg(-1); L30). Fish held at 19 degrees C had a reduction in the daily feed intake, growth and feed utilization of more than 50% compared to the controls. Fish at 19 degrees C retained little ingested fat, and high maintenance cost lead to depleted endogenous energy body reserves. Circulating ghrelin concentration and stomach ghrelin-1 and hypothalamus growth hormone secretagogue receptor la-like receptor (GHSR1a-LR) mRNA levels were significantly reduced in salmon at 19 degrees C. An increasing number of fish kept at 19 degrees C had empty gastrointestinal tract after 21 days (11-67%) and 56 days (56-100%), with the highest numbers in fish fed the 134 diet. We suggest that lower circulating ghrelin during negative energy homeostasis induce down-regulation of GHSR1a-LR, neuropeptide V. and anorexigenic factors at transcriptional levels in the hypothalamus, which over time lead to a voluntary anorexia development in adult salmon held at 19 degrees C. Reduction of feed intake and growth may be an important coping strategy for salmon during elevated temperatures. (C) 2011 Elsevier Inc. All rights reserved.