Leucine did not stimulate growth and accretion in either stressed or unstressed Atlantic salmon

The aim of the current trial was to test whether leucine affected growth and accretion including test any effects on leucine upon stress. Quadruplicate tanks each containing 50 Atlantic salmon (Salmo salar) (mean start body weight of 524 ± 28 g) were fed diets containing 27.3, 30.0, 35.0 and 41.0 g leucine/kg diet for 74 days. Two tanks per dietary group were exposed to a stressor (5 min chasing) three days a week to test whether enriched leucine diet aid coping with chronic stress, while two tanks per dietary groups were left unstressed. The stressed fish consumed less feed and grew less than the unstressed fish, irrespective of diet. Leucine inclusion did not affect protein accretion, but leucine retention declined with increasing dietary leucine in both stressed and unstressed fish. No difference between the stressed or unstressed fish was present. Leucine did not affect relative liver size, but unstressed fish had slightly higher relative liver size compared with stressed fish (p = 0.05). Free leucine in the muscle and liver was not affected by dietary leucine, but unstressed fish had higher concentration of valine and isoleucine in the muscle compared with the stressed fish. Muscle of fish fed elevated leucine had lower mRNA expression of murf1 (p = 0.037) and higher expression of ppara (p = 0.012). Muscle of stressed fish had higher expression of the oxydative genes mnsod (p = 0.049) and catalase (p = 0.037) compared with the fish left unstressed, while in liver, there were no differences of expression of any of the genes tested. In conclusion, diets enriched in leucine had minor effects and neither protein accretion nor growth was affected in either stressed or unstressed fish.publishedVersio

Anorectic role of high dietary leucine in farmed Atlantic salmon (Salmo salar L.): Effects on feed intake, growth, amino acid transporters and appetite-control neuropeptides.

Leucine has been identified to modulate feed intake and energy homeostasis in fish as in other vertebrates. Under allostatic conditions, energy expenditure may change, and adjustments to the processes that govern the energy homeostatic system may be necessary. We investigated the responsiveness of appetite-related neuropeptides involved in feed intake regulation in Atlantic salmon (Salmo salar) reared with high (35 g/kg leucine) or control (27.3 g/kg leucine) leucine-supplemented diets and/or under chronic stressor conditions (chasing) for eight weeks. We also analysed the response of amino acid transporters potentially involved in uptake of branched-chain amino acids (BCAA), including leucine, into areas of the brain where nutrient sensors may signal locally or to other areas involved in appetite control. At the end of the experiment, all fish were subjected to a novel-acute stressor (confinement). Our results show that fish fed with high leucine diet had a lower feed intake, growth, and hepatosomatic index (HSI) when compared to fish fed control leucine diet. In addition, increased mRNA expression of amino acid solute carrier (slc) genes in the diencephalon, and genes related to appetite control, such as proopiomelanocortin a1 (pomca1), in both the diencephalon and telencephalon, imply their involvement in leucine anorectic effect. Stress, as high leucine, reduced feed intake, growth and HSI of fish fed control or high leucine diet and antagonized the high leucine effect on the slc genes mRNA expression. An increase of neuropeptide y a1 (npya1) was observed both due to high dietary leucine and/or stress treatment which may represent a compensatory regulatory mechanism with the aim to reverse the decrease in feed intake. In summary, our results confirm an anorectic role of high dietary leucine via the activation of amino acid sensing mechanisms in the brain. Further, corticotropin-releasing hormone 1 b1 (crh1b1) and npya1 showed to play a role in the regulation of appetite in Atlantic salmon under stress conditions and/or high leucine levels.publishedVersio

Hormonal control of tryptic enzyme activity in Atlantic cod larvae (Gadus morhua): Involvement of cholecystokinin during ontogeny and diurnal rhythm

Highlights • We describe the ontogenetic development of CCK and tryptic enzyme activity in larval cod • CCK is known to play a key role in regulating digestive processes • CCK concentrations increased during ontogeny suggesting a growing role in regulating digestive processes • A short-term experiment reveals a feedback mechanism between CCK and tryptic enzyme activity • Cod larvae have limited regulatory and digestive capacity to handle several meals in a short period The ontogenetic development of the gut hormone cholecystokinin (CCK) and the key proteolytic enzyme trypsin was described in Atlantic cod larvae (Gadus morhua) from first-feeding until 38 days post first-feeding (dpff). CCK is known to play a major role in the endocrine control of digestive processes in mammals and adult fish, but its regulatory role in the larval stages of marine fish is largely unknown. Only small amounts of CCK were found in the body (excluding head) in cod larvae at first-feeding, but CCK levels increased exponentially with development, suggesting a more pronounced role of CCK during ontogeny. Tryptic enzyme activity increased slightly until a standard length of ca. 8 mm (approx. 33 days dpff) with a significant increase in larvae larger than 8 mm standard length, indicating limited digestive capacity in the early stages. To entangle the short-term feedback mechanism between CCK and tryptic enzyme activity, we conducted a 12 hour feeding experiment at 21 dpff. Cod larvae receiving only algae revealed a noticeable response in tryptic enzyme activity within two hours in the morning, whereas larvae fed algae and rotifers at the same time showed a slightly delayed response up to four hours. Tryptic enzyme activity remained low in the group receiving only algae as well as the two fed groups in the afternoon. No reaction in tryptic enzyme activity was observed in larvae that received a second meal of rotifers in the afternoon, indicating limited regulatory and digestive capacity to handle several meals in a short period. CCK levels remained relatively constant throughout the day but increased in the afternoon in all three groups when tryptic enzyme activity was low, suggesting that a negative feedback mechanism between CCK and tryptic enzyme activity is present in larval cod at least from 21 dpff

Leucine did not stimulate growth and accretion in either stressed or unstressed Atlantic salmon

The aim of the current trial was to test whether leucine affected growth and accretion including test any effects on leucine upon stress. Quadruplicate tanks each containing 50 Atlantic salmon (Salmo salar) (mean start body weight of 524 ± 28 g) were fed diets containing 27.3, 30.0, 35.0 and 41.0 g leucine/kg diet for 74 days. Two tanks per dietary group were exposed to a stressor (5 min chasing) three days a week to test whether enriched leucine diet aid coping with chronic stress, while two tanks per dietary groups were left unstressed. The stressed fish consumed less feed and grew less than the unstressed fish, irrespective of diet. Leucine inclusion did not affect protein accretion, but leucine retention declined with increasing dietary leucine in both stressed and unstressed fish. No difference between the stressed or unstressed fish was present. Leucine did not affect relative liver size, but unstressed fish had slightly higher relative liver size compared with stressed fish (p = 0.05). Free leucine in the muscle and liver was not affected by dietary leucine, but unstressed fish had higher concentration of valine and isoleucine in the muscle compared with the stressed fish. Muscle of fish fed elevated leucine had lower mRNA expression of murf1 (p = 0.037) and higher expression of ppara (p = 0.012). Muscle of stressed fish had higher expression of the oxydative genes mnsod (p = 0.049) and catalase (p = 0.037) compared with the fish left unstressed, while in liver, there were no differences of expression of any of the genes tested. In conclusion, diets enriched in leucine had minor effects and neither protein accretion nor growth was affected in either stressed or unstressed fish

Leucine did not stimulate growth and accretion in either stressed or unstressed Atlantic salmon

The aim of the current trial was to test whether leucine affected growth and accretion including test any effects on leucine upon stress. Quadruplicate tanks each containing 50 Atlantic salmon (Salmo salar) (mean start body weight of 524 ± 28 g) were fed diets containing 27.3, 30.0, 35.0 and 41.0 g leucine/kg diet for 74 days. Two tanks per dietary group were exposed to a stressor (5 min chasing) three days a week to test whether enriched leucine diet aid coping with chronic stress, while two tanks per dietary groups were left unstressed. The stressed fish consumed less feed and grew less than the unstressed fish, irrespective of diet. Leucine inclusion did not affect protein accretion, but leucine retention declined with increasing dietary leucine in both stressed and unstressed fish. No difference between the stressed or unstressed fish was present. Leucine did not affect relative liver size, but unstressed fish had slightly higher relative liver size compared with stressed fish (p = 0.05). Free leucine in the muscle and liver was not affected by dietary leucine, but unstressed fish had higher concentration of valine and isoleucine in the muscle compared with the stressed fish. Muscle of fish fed elevated leucine had lower mRNA expression of murf1 (p = 0.037) and higher expression of ppara (p = 0.012). Muscle of stressed fish had higher expression of the oxydative genes mnsod (p = 0.049) and catalase (p = 0.037) compared with the fish left unstressed, while in liver, there were no differences of expression of any of the genes tested. In conclusion, diets enriched in leucine had minor effects and neither protein accretion nor growth was affected in either stressed or unstressed fish