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This study aimed to evaluate the effect of diets including 10%, 20%, and 30% of black soldier fly larvae (Hermetia illucens) meal (HM) (diets HM10, HM20, and HM30, respectively), replacing 17%, 35%, and 52% of fishmeal (FM), on growth performance, whole-body composition and fatty acid (FA) profile, plasma biochemistry, and intermediary metabolism of meagre (Argyrosomus regius) juveniles. For that purpose, triplicate groups of 18.0 ± 0.02 g fish were fed a control diet (CTR) without HM, and the experimental diets for 9 weeks. Growth, feed efficiency, protein efficiency ratio, nitrogen and energy retentions linearly decreased with the increase of dietary HM level. With the exception of ash, whole-body composition was not linearly affected by dietary HM inclusion. Regarding whole-body FA profile, total saturated fatty acids (SFA), SFA: polyunsaturated fatty acids (PUFA) ratio, and total n-6PUFA linearly increased with increasing levels of dietary HM, while total n-3PUFA, n-3 long chain PUFA (LC-PUFA), n-3:n-6 ratio, and unsaturation index linearly decreased with increasing levels of HM in the diets. Docosahexaenoic acid (DHA) whole-body retention linearly decreased while lauric acid (12:0) retention increased with the increase of HM in the diet. Plasma glucose linearly increased, while plasma triglycerides and total lipids decreased with the dietary level of HM. Hepatic amino acid catabolic (alanine aminotransferease and aspartate aminotransferease), and lipogenic (glucose-6-phosphate dehydrogenase and malic enzyme) enzymes activities were unaffected by diet composition, whereas lipid catabolic (3-hydroxyacyl-CoA dehydrogenase) enzyme activity linearly decreased with dietary HM level. Glutamate dehydrogenase, an amino acid catabolic enzyme, was lower in fish fed the HM20 diet than the other HM-including diets. Overall, 10% of HM, corresponding to 17% of FM replacement, might be included in meagre diets without major adverse effects on growth, feed utilization, whole-body composition and FA profile.

International audience; The aim of the present study was to assess the impact of an acute handling stress on hepatic oxidative status of European sea bass (Dicentrarchus labrax) juveniles fed diets differing in lipid so urce and carbohydrate content. For that purpose, four diets were formulated with fish oil (FO) and vegetable oils (VO) as lipid source and with 20 or 0% gelatinized starch as carbohydrate source. Triplicate groups of fish with 74 g were fed each diet during 13 weeks and then subjected to an acute handling stress. Stress exposure decreased hematocrit (Ht) and hemoglobin (Hb) levels. Independent of dietary treatment, stress exposure increased hepatic lipid peroxidation (LPO). Stressed fish exhibited lower glucose 6-phosphate dehydrogenase (G6PD), catalase (CAT), and superoxide dismutase (SOD) activities, independent of previous nutritional history. In the VO groups, stress exposure increased glutathione peroxidase (GPX) activity. Diet composition had no effect on Ht and Hb levels. In contrast, dietary carbohydrate decreased hepatic LPO and CAT activity and increased glutathione reductase (GR) and G6PD activities. Dietary lipids had no effect on LPO. Fish fed the VO diets exhibited higher G6PD activity than fish fed the FO diets. In conclusion, dietary carbohydrates contributed to the reduction of oxidative stress in fish. However, under the imposed handling stress conditions, liver enzymatic antioxidant mechanisms were not enhanced, which may explain the overall increased oxidative stress.

For an increased incorporation of plant ingredients in aquafeeds at the expense of fish meal (FM) and fish oil (FO), more knowledge is needed on the effects at the intestine level of dietary vegetable oils (VO) and carbohydrates (CH), and of possible interactions. For that purpose, in this study, the activities of digestive pancreatic enzymes (amylase, lipase, total alkaline proteases), gut microbiota, and histomorphology were assessed in gilthead sea bream (IBW 71.0 ± 1.5 g) fed four diets differing in lipid source (FO or a blend of VO) and carbohydrate content (0% or 20% gelatinized starch) for 81 days. No major changes in digestive enzyme activities were noticed in fish fed the experimental diets. Dietary VO, but not CH content, modified intestinal microbial profile, by increasing the similarity of bacterial communities. Especially when combined with CH, dietary VO promoted abnormal enterocyte architecture. Liver histology was also accessed, and an increased cytoplasmic vacuolization of hepatocytes was related with dietary CH inclusion, being only significantly different in fish fed FO-based diets. Overall, nutritional interactions between dietary lipid source and carbohydrate content were not observed on digestive enzyme activities and microbial profile. However, the intestine histological modifications observed in fish fed the VOCH+ diet suggest a negative interaction between dietary VO and CH. This requires a more in depth assessment in future studies as it can have negative consequences at a functional level.

A digestibility trial was performed with gilthead sea bream juveniles (IBW = 72 g) fed four diets differing in lipid source (fish oil, FO; or a blend of vegetable oil, VO) and starch content (0 %, CH−; or 20 %, CH+) to evaluate the potential interactive effects between carbohydrates and VO on the processes involved in digestion, absorption and transport of lipids and glucose. In fish fed VO diets a decrease in lipid digestibility and in cholesterol (C), High Density Lipoprotein(HDL)-C and Low Density Lipoprotein (LDL)-C (only in CH+ group) were recorded. Contrarily, dietary starch induced postprandial hyperglycemia and time related alterations on serum triacylglycerol (TAG), phospholipid (PL) and C concentrations. Fish fed a CH+ diet presented lower serum TAG than CH− group at 6 h post-feeding, and the reverse was observed at 12 h post-feeding for TAG and PL. Lower serum C and PL at 6 h post-feeding were recorded only in VOCH+ group. No differences between groups were observed in hepatic and intestinal transcript levels of proteins involved in lipid transport and hydrolysis (FABP, DGAT, GPAT, MTP, LPL, LCAT). Lower transcript levels of proteins related to lipid transport (ApoB, ApoA1, FABP2) were observed in the intestine of fish fed the CH+ diet, but remained unchanged in the liver. Overall, transcriptional mechanisms involved in lipid transport and absorption were not linked to changes in lipid serum and digestibility. Dietary starch affected lipid absorption and transport, probably due to a delay in lipid absorption. This study suggests that a combination of dietary VO and starch may negatively affect cholesterol absorption and transport.

The impact of replacing circa 70 % fish oil (FO) by a vegetable oil (VO) blend (rapeseed, linseed, palm oils; 20:50:30) in diets for European sea bass juveniles (IBW 96 ± 0.8 g) was evaluated in terms of activities of digestive enzymes (amylase, lipase, alkaline phosphatase, trypsin and total alkaline proteases) in the anterior (AI) and posterior (PI) intestine and tissue morphology (pyloric caeca—PC, AI, PI, distal intestine—DI and liver). For that purpose, fish were fed the experimental diets for 36 days and then liver and intestine were sampled at 2, 6 and 24 h after the last meal. Alkaline protease characterization was also done in AI and PI at 6 h post-feeding. Dietary VO promoted higher alkaline phosphatase activity at 2 h post-feeding in the AI and at all sampling points in the PI. Total alkaline protease activity was higher at 6 h post-feeding in the PI of fish fed the FO diet. Identical number of bands was observed in zymograms of alkaline proteases of fish fed both diets. No alterations in the histomorphology of PC, AI, PI or DI were noticed in fish fed the VO diets, while in the liver a tendency towards increased hepatocyte vacuolization due to lipid accumulation was observed. Overall, and with the exception of a higher intestine alkaline phosphatase activity, 70 % FO replacement by a VO blend in diets for European sea bass resulted in no distinctive alterations on the postprandial pattern of digestive enzyme activities and intestine histomorphology.

This study aims to evaluate the effects of dietary arginine (Arg) surplus on gilthead sea bream growth, intestinal nutrient absorption capacity, hepatic and intestinal amino acid (AA) metabolism, and oxidative status. For that purpose a 6 weeks growth trial was performed with gilthead sea bream juveniles fed four isolipidic (18%) and isoproteic (44%) diets supplemented with 0, 0.5, 1 and 2% Arg. Dietary Arg did not affect fish growth performance, feed and nitrogen utilization, body composition, and activity of the main AA catabolic enzymes in liver and intestine. Similarly, intestinal nutrient absorption capacity, evaluated by intestinal brush border membrane vesicles technique, was also unaffected by the dietary Arg surplus. On the other hand, enzymatic antioxidant response was modulated by dietary Arg increment, which led to a reduced glutathione peroxidase activity in the liver and the intestine and increased superoxide dismutase activity in the intestine, but did not affect the overall lipid peroxidation values. Some differences in liver and intestine antioxidant enzymatic responses were identified, with the liver showing higher catalase and glucose-6-phosphate dehydrogenase activities, while the intestine presented higher glutathione peroxidase and glutathione reductase activities. Overall, dietary Arg excess showed limited potential to enhance gilthead sea bream performance and intestinal nutrient absorption capacity, but it was shown to modulate hepatic and intestinal antioxidant defences, without affecting overall lipid peroxidation. Statement of relevance Recently some fish species have been shown to benefit from dietary arginine surplus, while evidences also exist of an Arg-Lys antagonism in other fish species. This manuscript gives further insight on the potential of dietary arginine supplementation in gilthead sea bream, a major aquaculture species in the Mediterranean.

This study investigated the effects of dietary lipid source and carbohydrate content on liver and intestine oxidative status of gilthead sea bream juveniles, by assessing antioxidant defences enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione peroxidase, GPX; glutathione reductase, GR; and glucose-6-phosphate dehydrogenase, G6PD); total, reduced, and oxidized glutathione (GSH); and lipid peroxidation (LPO). Fish were fed for 13 weeks with four diets (2 × 2 factorial design) differing in lipid source (Fish oil- FO or a blend of vegetable oil-VO) and carbohydrate level (0 or 20% of digestible starch). Dietary VO reduced liver and intestine LPO, and enhanced liver GSH redox status (total and reduced GSH), GPX, GR, and G6PD activities, while in the intestine a decrease of G6PD activity and an increase of catalase activity and of reduced GSH (only in the carbohydrate diet) were recorded. Dietary carbohydrate promoted an increase of hepatic SOD and G6PD activities, and a decrease of CAT activity, total, oxidized, and reduced GSH, LPO, and oxidative stress index (OSI) (only in the FO diet). In the intestine, dietary carbohydrate did not induce alterations in LPO or enzymatic antioxidant defences but negatively affected GSH redox status (OSI, reduced and oxidized GSH). Overall, few interactions between dietary lipid source and carbohydrates were recorded. Dietary VO appeared to have a protective role against LPO in both tissues. Dissimilarities in liver and intestine susceptibility to LPO by dietary carbohydrate may reflect differences in glucose and GSH metabolism in the two tissues. Statement of relevance Plant related macronutrients improve fish oxidative status.

A digestibility trial was conducted to evaluate the effects of dietary fish oil (FO) replacement by a vegetable oil blend(VO) (rapeseed, linseed and palm oils) on nutrient digestibility, lipid absorption and transport and lipid and carbohydratemetabolic pathways of Dicentrarchus labrax juveniles. Following 36 days, the liver and intestine of fish were sampled 6 h after the last meal. Remaining fish were fed one more week and blood was collected at different postprandial time intervals. Dietary VO decreased apparent digestibility coefficients (ADC) of lipid and energy. Among the serum parameters analysed, only high-density lipoprotein was affected, being higher in VO group. Hepatic and intestinal expression of genes related to lipid transport and lipoprotein metabolism (FABP, DGAT, ApoB, ApoA4, ApoA1, MTP) showed no differences in transcript levels No alteration in genes related to cholesterol biosynthesis (HMGCR), glucose transport (GLUT2) or metabolism (GK, PK, G6Pase and PEPCK) in the liver and intestine was found. However, hepatic transcript levels of FADS2and elovl5 were up-regulated in VO group. In conclusion, replacement of FO by VO did not induce major alterations at molecular and biochemical levels, although a nutritional modulation of LC-polyunsaturated fatty acids biosynthesispathway was observed

Plant feedstuffs (PF) are rich in carbohydrates, which may interact with lipid metabolism. Thus, when considering dietary replacement of fishery by-products with PF, knowledge is needed on how dietary lipid source (LS) and carbohydrates affect lipid metabolism and other metabolic pathways. For that purpose, a 73-d growth trial was performed with European sea bass juveniles (IBW 74 g) fed four diets differing in LS (fish oil (FO) or a blend of vegetable oils (VO)) and carbohydrate content (0 % (CH–) or 20 % (CH+) gelatinised starch). At the end of the trial no differences among diets were observed on growth and feed utilisation. Protein efficiency ratio was, however, higher in the CH+ groups. Muscle and liver fatty acid profiles reflected the dietary LS. Dietary carbohydrate promoted higher plasma cholesterol and phospholipids (PL), whole-body and hepatic (mainly 16 : 0) lipids and increased muscular and hepatic glycogen. Except for PL, which were higher in the FO groups, no major alterations between FO and VO groups were observed on plasma metabolites (glucose, TAG, cholesterol, PL), liver and muscle glycogen, and lipid and cholesterol contents. Activities of glucose-6-phosphate dehydrogenase and malic enzyme – lipogenesis-related enzymes – increased with carbohydrate intake. Hepatic expression of genes involved in cholesterol metabolism was up-regulated with carbohydrate (HMGCR and CYP3A27) and VO (HMGCR and CYP51A1) intake. No dietary regulation of long-chain PUFA biosynthesis at the transcriptional level was observed. Overall, very few interactions between dietary carbohydrates and LS were observed. However, important insights on the direct relation between dietary carbohydrate and the cholesterol biosynthetic pathway in European sea bass were demonstrated.

This study aimed to evaluate the effects of dietary lipid source and carbohydrate content on the oxidative status of European sea bass (Dicentrarchus labrax) juveniles. For that purpose, four diets were formulated with fish oil (FO) and vegetable oils (VO) as the lipid source and with 20 or 0 % gelatinised starch as the carbohydrate source, in a 2×2 factorial design. Liver and intestine antioxidant enzyme activities (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD)), hepatic and intestinal lipid peroxidation (LPO), as well as hepatic oxidative stress index (OSI), were measured in fish fed the experimental diets for 73 d (n9 fish/diet). Carbohydrate-rich diets promoted a decrease in hepatic LPO and OSI, whereas the lipid source induced no changes. Inversely, dietary lipid source, but not dietary carbohydrate concentration, affected LPO in the intestine. Lower intestinal LPO was observed in VO groups. Enzymes responsive to dietary treatments were GR, G6PD and CAT in the liver and GR and GPX in the intestine. Dietary carbohydrate induced GR and G6PD activities and depressed CAT activity in the liver. GPX and GR activities were increased in the intestine of fish fed VO diets. Overall, effects of diet composition on oxidative status were tissue-related: the liver and intestine were strongly responsive to dietary carbohydrates and lipid sources, respectively. Furthermore, different metabolic routes were more active to deal with the oxidative stress in the two organs studied.

European sea bass and gilthead sea bream are two major marine finfish species reared in the Mediterranean region. Feeds for these species have high protein levels, usually supplied by fish meal. Research on alternatives to fish meal is mainly focused on plant protein feedstuffs, which are generally high in carbohydrates. Therefore, understanding the potential use of dietary carbohydrate is crucial for better utilization of such feedstuffs in the diets for these species. Factors that affect carbohydrate digestibility, metabolic utilization, as well as regulation of glucose metabolism are discussed. Data show that to ensure high digestibility, growth, and feed utilization, diets for these species should include around 20% digestible carbohydrate. Digestibility of native starch is high (above 70%) in both species, and it is further improved by processing starches (above 90%). Regarding carbohydrate complexity, it appears that European sea bass perform better with starch than glucose, while the opposite is tr...

International audience; Glucose plays a key role as energy source in the majority of mammals, but its importance in fish appears limited. Until now, the physiological basis for such apparent glucose intolerance in fish has not been fully understood. A distinct regulation of hepatic glucose utilization (glycolysis) and production (gluconeogenesis) may be advanced to explain the relative inability of fish to efficiently utilize dietary glucose. We summarize here information regarding the nutritional regulation of key enzymes involved in glycolysis (hexokinases, 6-phosphofructo-1-kinase and pyruvate kinase) and gluconeogenesis (phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase) pathways as well as that of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. The effect of dietary carbohydrate level and source on the activities and gene expression of the mentioned key enzymes is also discussed. Overall, data strongly suggest that the liver of most fish species is apparently capable of regulating glucose storage. The persistent high level of endogenous glucose production independent of carbohydrate intake level may lead to a putative competition between exogenous (dietary) glucose and endogenous glucose as the source of energy, which may explain the poor dietary carbohydrate utilization in fish.

The aim of this work was to elucidate if the previous results observed in hepatic glucokinase (GK) and glucose-6-phosphatase (G6Pase) activities in European sea bass and gilthead sea bream are due to temperature per se or to differences in feed intake at different water temperatures. For that purpose triplicate groups of fish (30 g initial body weight) were kept at 18 degrees C or 25 degrees C during two weeks and fed a fixed daily ration of a glucose-free or 20% glucose diet. At the end of the experimental period, plasma glucose levels in both species were not influenced by water temperature but were higher in fish fed the glucose diet. Higher hepatic GK activity was observed in the two fish species fed the glucose diet than the glucose-free diet. In the glucose fed groups, GK activity was higher at 25 degrees C than at 18 degrees C. Glucose-6-phosphatase activities in both species were not influenced by water temperature. In European sea bass and in contrast to gilthead sea bream it was observed an effect of dietary composition on G6Pase activities with surprising higher activities recorded in fish fed the glucose diet than in fish fed the glucose-free diet. Overall, our data strongly suggest that European sea bass and gilthead sea bream are apparently capable to strongly regulate glucose uptake by the liver but not glucose synthesis, which is even enhanced by dietary glucose in European sea bass. Within limits, increasing water temperature enhances liver GK but not G6Pase activities, suggesting that both species are more able to use dietary carbohydrates at higher rearing temperatures.

The aim of this trial was to evaluate the effect of dietary nucleic acids on ureagenesis and nitrogen balance in gilthead sea bream juveniles. For that purpose, 5 isonitrogenous (7.25% N) diets were formulated based on fish meal as protein source (FM-control diet) and to partially replace the fish meal nitrogen with two levels of nucleic acids (diets RNA1 and RNA2) or brewers yeast (diets BY1 and BY2). Each diet was fed for 10 weeks, to apparent visual satiety, to triplicate groups of 50 fish each with an average body weight of 12.7 g. Inclusion of nucleic acid N either as brewers yeast or RNA led to significant improvement of feed intake and growth, except for fish fed diet RNA2. There were no differences in final weight between groups fed the yeast- and the RNA-containing diets. Although there was an improvement of growth rate of fish fed the RNA or yeast containing diets, dietary nucleic acid supplementation did not have a clear N sparing effect. At the end of the trial there were no significant differences in whole body composition among groups, except for the lipid content which was significantly higher in fish fed the Y2 diet. Hepatic glutamate dehydrogenase activity levels did not differ among groups. Ornithine carbamyl transferase activities were very low in all groups, but appear to be induced by high levels of dietary RNA. Fish fed the yeast diets exhibited the highest arginase activity of all groups. No increase of uricase activities was observed in fish fed the RNA supplemented diets. Ammonia and urea excretion of fish fed the RNA-including diets was higher or significantly higher than in the other groups. Plasma urea levels were higher in fish fed the RNA diets than in the other groups confirming excretion data in that dietary nucleic acid influenced urea excretion through uricolysis. In conclusion, substitution of N supplied by fish meal by that supplied by brewers yeast had a positive effect on growth performance of sea bream, while dietary nucleic acid supplementation did not have a clear N sparing effect. At a dietary level of 11.5% of RNA extract, there was no improvement of fish performance compared to the control, possibly due to an insufficient capacity of fish to degrade high levels of nucleic acid. Data on excretion and plasma metabolites strongly suggest that purinolysis contributes also to ureogenesis in gilthead sea bream. (C) 2005 Elsevier B.V. All rights reserved.

A study was conducted to evaluate the effect of two dietary carbohydrate sources (waxy maize starch and glucose) on the metabolic adaptation of sea bass juveniles (initial weight: 24 g) to a heat shock treatment (temperature rise from 18 degrees C to 25 degrees C within 24 h). Two isonitrogenous and isolipidic diets were fon-nulated to contain 20% waxy maize starch (WS diet) or 20% glucose (GLU diet). Triplicate groups of fish were fed to near satiation for 4 weeks at both temperatures (18 degrees C and 25 degrees C). Then, fish previously maintained at 18 degrees C were submitted to a heat shock (18 degrees C to 25 degrees C) and continued to be fed with the same diets during I more week. The higher water temperature significantly improved growth performance, feed efficiency, as well as protein efficiency ratio, independently of diet. At 25 degrees C, but not at 18 degrees C, growth of fish fed the WS diet was higher than that of fish fed the GLU diet. Plasma glucose levels were higher in sea bass fed the GLU diet and not influenced by water temperature. Fish fed a glucose diet or reared at high temperatures (25 degrees C) showed enhanced liver glycolytic, lipogenic and gluconeogenic capacities compared to fish fed a starch diet or reared at low temperatures (18 degrees C). For the majority of the enzymes studied, I week seemed to be enough time for metabolic adaptation in sea bass submitted to an acute heat shock. Irrespective of carbohydrate source, HSP70 gene expression was similar in both cold water (18 degrees C) and warm water (25 degrees C) acclimated sea bass. A weak down regulation was observed after heat shock only in fish fed the GLU diet. This suggests that HSP70 gene expression is not affected by the rearing temperature per se. (c) 2006 Elsevier Inc. All rights reserved.

The solubility of protein nitrogen at pH 8 in the organisms used as live food for fish larvae (rotifers and Artemia) was determined and the molecular weight profile of soluble protein nitrogen was analysed by HPLC-gel filtration chromatography. Soluble nitrogen accounted for 61% of total nitrogen in microalgae-fed rotifers, 47% in starved rotifers and 54% in newly hatched Artemia. A remarkable similarity in the profile of molecular weight distribution of soluble nitrogen was noticed among these three types of live food. The molecular weights of soluble nitrogen was partitioned as follows, respectively, in rotifers and Artemia: 84–88% and 89% >500 Da (corresponding mainly to proteins, poly- and oligopeptides), 8–11% and 4% from 200 to 500 Da (corresponding mainly to di- and tripeptides), 3–4% and 7%

Ammonia and urea nitrogen excretion and oxygen consumption of diploid and triploid rainbow trout were measured at several evenly spaced intervals from egg fertilization until 8 days after complete yolksac absorption at a constant temperature of 12°C. The same parameters were also measured in embryos transferred to temperatures of 5 and 10°C on each measurement day, to estimate the effect of temperature on the utilization of the endogenous energy reserves in embryos in the same stage of development and having identical energy reserves. Metabolic characteristics were not significantly different between diploid and triploid embryos at any experimental temperature. At the constant temperature of 12°C, oxygen consumption and ammonia nitrogen excretion slowly increased before hatching. Thereafter both increased considerably until yolksac absorption was completed. In the starving fry, after yolk absorption, oxygen consumption decreased, while ammonia excretion continued to increase until the end of the trial. Urea nitrogen excretion did not show much change before hatching. Thereafter it increased for a few days and then declined until complete yolksac absorption. In starving alevins, urea excretion rates continued to increase. While oxygen consumption and ammonia excretion rates were directly related to temperature, urea excretion was not affected by temperature. Temperature considerably affected utilization of the endogenous energy substrates: less protein energy was used to cover the energy needs of the embryos at higher temperatures.