A three-phase excess post-exercise oxygen consumption in Atlantic salmon Salmo salar and its response to exercise training.

The recovery of oxygen uptake to the standard metabolic rate (SMR) following exhaustive chasing exercise in Atlantic salmon Salmo salar parr occurred in three phases (rapid, plateau and slow). The initial recovery phase lasted 0·7 h and contributed 16% to the total excess post-exercise oxygen consumption (EPOC). It was followed by a longer plateau phase that contributed 53% to the total EPOC. The slow recovery phase that completed recovery of SMR, which has not been reported previously, made a 31% contribution to the total EPOC. The plasticity of EPOC was demonstrated in exercise-trained fish. Exercise training increased EPOC by 39% when compared with control fish (mean ± S.E., 877·7 ± 73·1 v. 629·2 ± 53·4 mg O2 kg-1 , d.f. = 9, P < 0·05), with the duration of the plateau phase increasing by 38% (4·7 ± 0·58 v. 3·4 ± 0·16 h, d.f. = 9, P < 0·05) and the contribution of the slow phase to the total EPOC increasing by 80% (173·9 ± 23·9 v. 312·5 ± 50·4 mg O2 kg-1 , d.f. = 9, P < 0·05). As a result, the combination of the plateau and slow phases of exercise-trained fish increased by 47% compared with control fish (756·6 ± 71·4 v. 513·6 ± 43·1 mg O2 kg-1 ; d.f. = 9, P = 0·01). To substantiate the hypothesis that the plateau and slow recovery phase of EPOC was related to general metabolic recovery following exhaustive exercise, the time-course for recovery of SMR was compared with previously published metabolite recovery profiles. The final phase of metabolic recovery was temporally associated with the final phases of gluconeogenesis, lactate oxidation and muscle intracellular pH regulation. Therefore, the plasticity of the latter phase of EPOC agreed with the known effects of exercise training in fishes.

The effects of sustained aerobic swimming on osmoregulatory pathways in Atlantic salmon Salmo salar smolts.

Atlantic salmon Salmo salar smolts were exposed to one of the four different aerobic exercise regimens for 10 weeks followed by a 1 week final smoltification period in fresh water and a subsequent eight-day seawater transfer period. Samples of gill and intestinal tissue were taken at each time point and gene expression was used to assess the effects of exercise training on both branchial and intestinal osmoregulatory pathways. Real-time polymerase chain reaction (PCR) analysis revealed that exercise training up-regulated the expression of seawater relevant genes in the gills of S. salar smolts, including Na(+) , K(+) ATPase (nka) subunit α1b, the Na(+) , K(+) , 2 Cl(-) co-transporter (nkcc1) and cftr channel. These findings suggest that aerobic exercise stimulates expression of seawater ion transport pathways that may act to shift the seawater transfer window for S. salar smolts. Aerobic exercise also appeared to stimulate freshwater ion uptake mechanisms probably associated with an osmorespiratory compromise related to increased exercise. No differences were observed in plasma Na(+) and Cl(-) concentrations as a consequence of exercise treatment, but plasma Na(+) was lower during the final smoltification period in all treatments. No effects of exercise were observed for intestinal nkcc2, nor the Mg(2+) transporters slc41a2 and transient receptor protein M7 (trpm7); however, expression of both Mg(2+) transporters was affected by salinity transfer suggesting a dynamic role in Mg(2+) homeostasis in fishes.

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 °C while others were kept as controls at 14 °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 °C had a reduction in the daily feed intake, growth and feed utilization of more than 50% compared to the controls. Fish at 19 °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 1a-like receptor (GHSR1a-LR) mRNA levels were significantly reduced in salmon at 19 °C. An increasing number of fish kept at 19 °C had empty gastrointestinal tract after 21 days (11-67%) and 56 days (56-100%), with the highest numbers in fish fed the L34 diet. We suggest that lower circulating ghrelin during negative energy homeostasis induce down-regulation of GHSR1a-LR, neuropeptide Y, and anorexigenic factors at transcriptional levels in the hypothalamus, which over time lead to a voluntary anorexia development in adult salmon held at 19 °C. Reduction of feed intake and growth may be an important coping strategy for salmon during elevated temperatures.

Tetradecylthioacetic acid modulates cardiac transcription in Atlantic salmon, Salmo salar L., suffering heart and skeletal muscle inflammation.

Heart and skeletal muscle inflammation (HSMI) is a disease causing considerable mortality in farmed Atlantic salmon. We have previously reported that pre-feeding of tetradecylthioacetic acid (TTA) reduces the mortality during a natural outbreak of HSMI. In the present paper we show that in the cardiac ventricle, during HSMI infection, pre-feeding TTA increases the expression of the immune genes: TNFα, VCAM-1, IgM and CD8α. We also show that TTA increases the cardiosomatic index potentially by elevating cardiomyogenesis through activation of the cardiac transcription factors MEF2C and Nkx2.5. Using the recently published genomic sequence of a HSMI associated piscine reovirus (PRV), we could show that the PRV levels have no confounding effects on the mRNA expression of the investigated genes. The results suggest that TTA induced cardiac growth, together with an elevated cardiac recruitment of immune cells, which might lead to increased robustness during HSMI infection.

Increased survival by feeding tetradecylthioacetic acid during a natural outbreak of heart and skeletal muscle inflammation in S0 Atlantic salmon, Salmo salar L.

We have previously documented increased survival by feeding tetradecylthioacetic acid (TTA) during a natural outbreak of infectious pancreatic necrosis in post-smolt S1 Atlantic salmon. The aim of the present study was to test the effects of dietary TTA in S0 smolt at a location where fish often experience natural outbreaks of heart and skeletal muscle inflammation (HSMI) during their first spring at sea. The experimental groups were fed a diet supplemented with 0.25% TTA for a 6-week period prior to a natural outbreak of HSMI in May 2007. Relative percent survival for the groups fed TTA was 45% compared with control diets, reducing mortality from 4.7% to 2.5%. Expression of genes related to lipid oxidation was higher in cardiac ventricles from salmon fed TTA compared with controls. In addition, salmon fed TTA had periodically reduced levels of plasma urea, and increased cardiosomatic index and growth. Reduced mortality and increased growth after administration of TTA may be related to a combination of anti-inflammatory effects, and an altered metabolic balance with better protein conservation because of increased lipid degradation.

Conformational analysis of methotrexate.

Using classical potential functions, the conformation of methotrexate is obtained. Calculations show that glutamate side chain will not have much folding and the plane of pteridine ring would be tilted approximately with an angle of 30 degrees with respect to the plane of phenyl group.