Search

Optimizing the metabolic use of these carbohydrate-rich plant products in fish feeds could be achieved through nutritional programming strategies of fish larvae. The present study aims at testing the long-term effect of an early-life high-carbohydrate nutritional (34% of starch in the feed) stimulus in European sea bass (Dicentrarchus labrax), by examining several biochemical and molecular parameters involved in carbohydrate metabolism in sea bass larvae and juveniles, compared to a control group fed standard larval regime (phase 1). As awaited, specific activities of digestive enzymes, from pancreatic and intestinal segments, involved in glucide digestion (amylase, sucrase) were enhanced together with an up-regulation of glucokinase gene and down-regulation of glucose 6-phosphatase gene assayed in whole-body larvae fed the high-carbohydrate diet. However, this regime also induced a significant lowering in growth and survival. Six months later, while all the fish were fed the same standard diet, a first hypoxia challenge test allowed to distinguish two groups of fish according their nutritional history at larval stage: fish had been fed high-carbohydrate regime performed much better than control. When fed again during 2 months with a high-carbohydrate diet (phase 2), such larval nutritional history did not confer any subsequent “advantage” or “disadvantage” in term of carbohydrate metabolism and growth. A second hypoxia challenge test performed just after phase 2, did not confirm the first one. All together our results indicated that the larval conditioning may fade over time. It was suggested to apply regular nutritional stress pulses during the first months of fish life

Based on the concept of nutritional programming in mammals, we tested whether an acute hyperglucidic-hypoproteic stimulus during first feeding could induce long-term changes in nutrient metabolism in rainbow trout. Trout alevins received during the five first days of exogenous feeding either a hyperglucidic (40% gelatinized starch + 20% glucose) and hypoproteic (20%) diet (VLP diet) or a high-protein (60%) glucose-free diet (HP diet, control). Following a common 105-day period on a commercial diet, both groups were then challenged (65 days) with a carbohydrate-rich diet (28%). Short-and long-term effects of the early stimuli were evaluated in terms of metabolic marker gene expressions and intestinal microbiota as initial gut colonisation is essential for regulating the development of the digestive system. In whole alevins (short term), diet VLP relative to HP rapidly increased gene expressions of glycolytic enzymes, while those involved in gluconeogenesis and amino acid catabolism decreased. However, none of these genes showed persistent molecular adaptation in the liver of challenged juveniles (long term). By contrast, muscle of challenged juveniles subjected previously to the VLP stimulus displayed downregulated expression of markers of glycolysis and glucose transport (not seen in the short term). These fish also had higher plasma glucose (9 h postprandial), suggesting impaired glucose homeostasis induced by the early stimulus. The early stimulus did not modify the expression of the analysed metabolism-related microRNAs, but had short-and long-term effects on intestinal fungi (not bacteria) profiles. In summary, our data show that a short hyperglucidic-hypoproteic stimulus during early life may have a long-term influence on muscle glucose metabolism and intestinal microbiota in trout.

World aquaculture is growing (+ 8% per year) to meet the increasing demand of fish for human consumption that capture by fisheries can no longer cover. Consequently, the need for aquafeed and feedstuffs is rising while volumes of fishmeal and fish oil, the traditional aquafeed ingredients, remain stable. More and more fishmeal and fish oil are substituted by plant products. Between 80 and 95% of fish meal can be replaced by a combination of plant protein sources providing the indispensable amino acids in sufficient quantity to meet the fish needs. Beyond this substitution rate, feed intake, feed efficiency and growth rate decrease and metabolic changes are observed despite the diets containing all the required nutrients. Fish oil can be replaced by a mix of vegetable oils without deleterious effect on fish growth and health, provided that the diet supplies essential fatty acids. Fatty acids requirements vary with species according to their capacity to synthesize EPA and DHA. However, in all species, fish oil substitution results in a reduction in the flesh content of these omega 3fatty acids. Research must continue to further reduce the reliance of aquaculture on fishery resources while ensuring an efficient fish production of high quality products with limited environmental impacts., L'aquaculture mondiale se développe (+ 8% par an) pour répondre à une demande croissante des consommateurs que les captures de pêche ne peuvent plus couvrir. Les besoins en aliments piscicoles et donc en matières premières s’accroissent, alors que les volumes de farines et huiles de poisson, ingrédients traditionnels des aliments aquacoles, ne peuvent augmenter. Selon les espèces, 80 à 95% de la farine de poisson peut être substituée par un mélange de sources protéiques végétales apportant les acides aminés indispensables en quantité suffisante pour couvrir les besoins des poissons. Au-delà de ce taux de remplacement, on observe une baisse de la consommation d'aliment, de l'efficience alimentaire et de la croissance, bien que les aliments contiennent les nutriments nécessaires aux poissons. Quant à l'huile de poisson, elle peut être remplacée jusqu’à 80 ou 100% par des huiles végétales sans effet délétère sur la croissance et la santé des poissons, à condition que le régime apporte en quantité suffisante les acides gras essentiels à la couverture des besoins, qui diffèrent selon l'espèce : contrairement aux poissons marins, les salmonidés disposent en effet d’une relative capacité de synthèse d’acides gras longs polyinsaturés omega 3 à partir de l’acide linoléique. La conséquence majeure est une baisse de la teneur de ces acides gras dans la chair. Les recherches doivent se poursuivre pour affranchir encore davantage l'aquaculture des produits de la pêche, en choisissant des matières premières alternatives qui garantissent une production piscicole efficace, des produits de haute qualité et des impacts environnementaux limités.

Sustainable aquaculture, which entails proportional replacement of fish-based feed sources by plant-based ingredients, is impeded by the poor growth response frequently seen in fish fed high levels of plant ingredients. This study explores the potential to improve, by means of early nutritional exposure, the growth of fish fed plant-based feed. Rainbow trout swimup fry were fed for 3 weeks either a plant-based diet (diet V, V-fish) or a diet containing fishmeal and fish oil as protein and fat source (diet M, M-fish). After this 3-wk nutritional history period, all V- or M-fish received diet M for a 7-month intermediate growth phase. Both groups were then challenged by feeding diet V for 25 days during which voluntary feed intake, growth, and nutrient utilisation were monitored (V-challenge). Three isogenic rainbow trout lines were used for evaluating possible family effects. The results of the V-challenge showed a 42% higher growth rate (P = 0.002) and 30% higher feed intake (P = 0.005) in fish of nutritional history V compared to M (averaged over the three families). Besides the effects on feed intake, V-fish utilized diet V more efficiently than M-fish, as reflected by the on average 18% higher feed efficiency (P = 0.003). We noted a significant family effect for the above parameters (P,0.001), but the nutritional history effect was consistent for all three families (no interaction effect, P.0.05). In summary, our study shows that an early shortterm exposure of rainbow trout fry to a plant-based diet improves acceptance and utilization of the same diet when given at later life stages. This positive response is encouraging as a potential strategy to improve the use of plant-based feed in fish, of interest in the field of fish farming and animal nutrition in general. Future work needs to determine the persistency of this positive early feeding effect and the underlying mechanisms.

For sustainable aquaculture, the removal of marine resource ingredients in fish diets is an important objective. While most studies focus on the replacement of fish oil by vegetable oil, little is known on the nutritional effects of presence (which corresponds to the control diet) or absence of dietary fish oil. We studied fatty acid composition of brush-border membranes and digestive enzyme activities of the intestine and measured the expression and activities of several enzymes involved in the hepatic intermediary metabolism of rainbow trout (Oncorhynchus mykiss) fed for 7 weeks with or without fish oil. The diets were pair-fed to ensure that fish fed either diet had comparable carbohydrate and protein intakes. Absence of fish oil significantly reduced growth rate, protein efficiency and plasma lipid components. Activities of intestinal digestive enzymes were significantly decreased in the anterior intestine in fish fed without fish oil. In liver, dietary fish oil removal did not affect the transcript levels or activities of the main enzymes involved in lipogenesis (fatty acid synthase) and fatty acid p-oxidation (3-hydroxyacyl-CoA dehydrogenase), glycolysis or amino acid oxidation. It lowered the expression of the genes coding for gluconeogenic enzymes (glucose-6-phosphatase and phosphoenolpyruvate carboxykinase), but their enzyme activities were not affected. The activities, but not gene expression of lipogenic enzymes, involved in NADPH and malonyl-CoA formation were also modified after fish oil removal as reflected by higher activities of isocitrate dehydrogenaselglucose-6-phosphate dehydrogenase and acetyl-CoA carboxylase enzymes. Overall, our results indicate that the intestinal digestive capacity was strongly modified by dietary fish oil removal, while hepatic intermediary metabolism was only marginally affected, in fed rainbow trout.

Based on the concept of nutritional programming in higher vertebrates, we tested whether an acute hyperglucidic stimulus during early life could induce a long-lasting effect on carbohydrate utilization in carnivorous rainbow trout. The trout were fed a hyperglucidic diet (60% dextrin) at two early stages of development: either at first feeding Q days, stimulus 1) or after yolk absorption (5 days, stimulus 2). Before and after the hyperglucidic stimulus, they received a commercial diet until juvenile stage (> 10 g). Fish that did not experience the hyperglucidic stimuli served as controls. The short- and long-term effects of the stimuli were evaluated by measuring the expression of five key genes involved in carbohydrate utilization: a-amylase, maltase (digestion), sodium-dependent glucose cotransporter (SGLT1; intestinal glucose transport), and glucokinase and glucose-6-phosphatase, involved in the utilization and production of glucose, respectively. The hyperglucidic diet rapidly increased expressions of maltase, a-arrylase, and glucokinase in stimulus I fish and only of maltase in stimulus 2 fish, probably because of a lower plasticity at this later stage of development. In the final challenge test with juveniles fed a 25% dextrin diet, both digestive enzymes were upregulated in fish that had experienced the hyperglucidic stimulus at first feeding, confirming the possibility of modification of some long-term physiological functions in rainbow trout. In contrast, no persistent molecular adaptations were found for the genes involved in glucose transport or metabolism. In addition, growth and postprandial glycentia were unaffected by the stimuli. In summary, our data show that a short hyperglucidic stimulus during early trout life may permanently influence carbohydrate digestion.

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.

Our objective was to understand the reasons behind the persistent postprandial hyperglycemia in rainbow trout (Oncorhynchus mykiss). We hypothesized that in this species, high levels of dietary protein could increase the hepatic production of glucose, irrespective of the dietary carbohydrate supply. We fed juvenile rainbow trout four diets containing graded levels of protein for 14 d. Pair-feeding was employed to keep lipid and carbohydrate intakes constant. Six hours after feeding, as postulated, activities and mRNA levels of gluconeogenic enzymes (glucose-6-phosphatase, fructose-1,6-bisphosphatase) increased with increasing dietary protein (P < 0.05). However, in fish with a very low protein intake, there was a very strong increase in plasma glucose (18 mmol/L) that was also associated with a high capacity to store excess glucose as indicated by altered pyruvate kinase activity, glucokinase activity, and hepatic glycogen and fat concentrations (P < 0.05). In conclusion, at the same level of carbohydrate intake, a low dietary protein intake was associated with an unexplained increase in glycemia, which was probably responsible for the decrease in hepatic gluconeogenic enzyme expression. The effect of dietary protein on low carbohydrate utilization in this species remains unclear.