Pre and postprandial regulation of ghrelin, amino acids and IGF1 in Atlantic salmon (Salmo salar L.) at optimal and elevated seawater temperatures

Atlantic salmon farmed in seacage facilities are exposed to changing environmental conditions. While growth decline under lower water temperatures are reasonably well understood, the mechanisms behind production decline under high water temperatures are yet to be well elucidated and have been hampered by a lack of data describing pre- and postprandial patterns of endocrine fluctuation. The present research therefore aims to determine whether peak nutrient flux into the blood plasma is the most appropriate time point to investigate the endocrine regulation of growth and appetite under conditions of normal and high temperature, and to investigate the interrelationship between appetite and growth on a pre- and post-prandial time scale. Two experiments are presented which examine ghrelin (GHRL) as an indicator of appetite stimulation, the GH–IGF (growth hormone–insulin-like growth factor) system to describe growth-regulating processes and free amino acids (FAA) to indicate postprandial nutrient influx and link appetite and anabolic processes. Postprandial sampling of plasma and white muscle tissue from short-term adapted postsmolt was conducted at 13 °C and 19 °C at 4, 8, 12, 16, 20 and 24 hours (h). The same samples were taken from long-term adapted big salmon at 12 °C, − 4, − 2, − 1, 0 h pre-prandially and 2, 3, 4 and 6 h post-prandially. While limited relationship between plasma ghrelin concentration and meal times was found for short term adapted postsmolt, clear ghrelin peaks were described for long term adapted salmon prior to the timing of anticipated meals. Possible explanations and consequences to experimental design in this area will be discussed. Postprandial FAA in plasma and white muscle from postsmolt was reduced at 19 °C compared to 13 °C and plasma levels peaked 8 h post-prandially. Muscle Igf1 mRNA expression levels were consistently higher at 13 °C than 19 °C, with no clear postprandial patters. In contrast, plasma IGF-1 concentration was relatively constant over time at 12 °C and 13 °C, but significantly declined from 20 h postprandially at 19 °C. GH receptor (ghr1) mRNA expression in muscle was unaffected by temperature, peaking 4 h post-prandially at both temperatures. This paper describes growth and appetite-regulating processes under conditions of normal and elevated temperature for Atlantic salmon, which is fundamental to our understanding of growth limitations inherent to high water temperature situations

Impact of high water carbon dioxide levels on Atlantic salmon smolts (<i>Salmo salar</i> L.): Effects on fish performance, vertebrae composition and structure

The role of high carbon dioxide (CO2) levels on fish performance, bone structure/composition and as a potential cause of spinal deformities was studied. Two groups of fish were exposed to a low (control) and a high level of CO, for 135 days during the freshwater period. After smoltification, the fish were transferred to seawater and followed up for 517 days until they reached harvest weight (3.1 kg BW). Differences in body weight between the control and high CO2 groups were observed. At the end of the freshwater period, average weight in the group exposed to high CO2 levels was 20.9% lower than in the control group. Specific growth rates (SGR) from the start of the experiment (10 g BW) to smolt stage were 1.63 +/- 0.04 and 1.36 +/- 0.01 for the control group and the high CO2 group, respectively. Differences in body weight were maintained during the initial stages of the seawater period, but were not observed at harvest weight. Nephrocalcinosis was not observed in any of the experimental groups at the end of the freshwater period and no external signs of spinal deformities were observed either at smolt stage or at harvest weight. X-rays revealed mild abnormalities in some vertebrae bodies, which could not be related to any experimental group. Despite the lack of signs of pathological bone alterations, the histological examination suggested that the exposure to high CO2 levels resulted in an increase in trabeculae volume and a higher rate of bone remodeling at the end of the freshwater period. Furthermore, fish exposed to a high CO2 level presented a higher bone ash content at the end of the freshwater period. These differences could not be observed at the end of the grow-out period