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WOS:000569774900004; Coastal nursery areas are subjected to a wide range of natural and anthropogenic stressors, including global warming, which indirectly influence trophic food webs. A global rarefaction of n-3 polyunsaturated fatty acids (PUFA) in trophic networks is in progress. The aim of this study was to assess the effect of a reduction in the dietary availability of n-3 PUFA on some molecular and biochemical parameters related to lipid metabolism and oxidative stress response in juvenile European sea bass (Dicentrarchus labrax) raised at two temperatures (15 degrees C and 20 degrees C). Fish were fed for five months with a reference diet (RD; 1.65% n-3 PUFA on a dry matter basis, DM), used as a proxy of trophic networks where n-3 PUFA is plentiful, and a lower n-3 PUFA diet (LD; 0.73% n-3 PUFA DM), designed to mimic a decrease in n-3 PUFA resulting from global changes (the n-3 PUFA levels tested remained above the nutritional minimum required for this species). Results showed that diet did not affect the hepatic expression of some mRNA coding for transcriptional factors involved in regulating the metabolic pathways related to fatty acid bioconversion. Although our molecular analysis was limited to transcript expression, these data suggest the presence of a threshold in the nutritional supply of PUFA above which the activation of these molecular pathways does not occur. However, the expression for most of the transcripts tested was up-regulated at 20 degrees C. Despite the high peroxidation index in fish fed RD, very few modifications of the oxidative stress response were associated with diet. At 20 degrees C, an increase of the enzymatic antioxidant response was observed, but there was no correlation with the peroxidation index or malondialdehyde products.

Microplastics are present in marine habitats worldwide and may be ingested by low trophic organisms such as fish larvae, with uncertain physiological consequences. The present study aims at assessing the impact of polyethylene (PE 10-45 mu M) microbeads ingestion in European sea bass (Dicentrarchus labrax) larvae. Fish were fed an inert diet including 0, 10(4) and 10(5) fluorescent microbeads per gram from 7 until 43 days post-hatching (dph). Microbeads were detected in the gastrointestinal tract in all fish fed diet incorporating PE. Our data revealed an efficient elimination of PE beads from the gut since no fluorescent was observed in the larvae after 48 h depuration. While the mortality rate increased significantly with the amount of microbeads scored per larvae at 14 and 20 dph, only ingestion of the highest concentration slightly impacted mortality rates. Larval growth and inflammatory response through Interleukine-1-beta (IL-1 beta) gene expression were not found to be affected while cytochrome-P450-1A1 (cyp1a1) expression level was significantly positively correlated with the number of microbeads scored per larva at 20 dph. Overall, these results suggest that ingestion of PE microbeads had limited impact on sea bass larvae possibly due to their high potential of egestion.

Ocean acidifcation is a recognized consequence\ud of anthropogenic carbon dioxide (CO2) emission in the\ud atmosphere. Despite its threat to marine ecosystems, little\ud is presently known about the capacity for fsh to respond\ud effciently to this acidifcation. In adult fsh, acid–base regulatory\ud capacities are believed to be relatively competent to\ud respond to hypercapnic conditions. However, fsh in early\ud life stage could be particularly sensitive to environmental\ud factors as organs and important physiological functions\ud become progressively operational during this period. In this\ud study, the response of European sea bass (Dicentrarchus\ud labrax) larvae reared under three ocean acidifcation scenarios,\ud i.e., control (present condition, PCO2 = 590 µatm,\ud pH total = 7.9), low acidifcation (intermediate IPCC scenario,\ud PCO2 = 980 µatm, pH total = 7.7), and high acidifcation\ud (most severe IPCC scenario, PCO2 = 1520 µatm,\ud pH total = 7.5) were compared across multiple levels of\ud biological organizations. From 2 to 45 days-post-hatching, the chronic exposure to the different scenarios had limited\ud infuence on the survival and growth of the larvae (in\ud the low acidifcation condition only) and had no apparent\ud effect on the digestive developmental processes. The high\ud acidifcation condition induced both faster mineralization\ud and reduction in skeletal deformities. Global (microarray)\ud and targeted (qPCR) analysis of transcript levels in\ud whole larvae did not reveal any signifcant changes in gene\ud expression across tested acidifcation conditions. Overall,\ud this study suggests that contemporary sea bass larvae\ud are already capable of coping with projected acidifcation\ud conditions without having to mobilize specifc defense\ud mechanisms.

International audience; Hemoglobins (Hb) play a critical role in satisfying the oxygen demand of vertebrate aerobic metabolism. The present study reports the characterization of the European sea bass (Dicentrarchus labrax) Hb genes, including genomic organization, phylogeny, and spatio-temporal gene expression. These Hb genes are divided into two unlinked clusters, the “MN” cluster containing eleven genes (five Hbα genes named MN-Hbα1-5 and six Hbβ genes named MN-Hbβ1–6) and the “LA” cluster consisting of three genes (two Hbα genes named LA-Hbα1-2 and one Hbβ gene named LA-Hbβ1). Comparative analysis of Hb amino acid sequences indicates that most of the important amino acid residues involved in hemoglobin-oxygen binding, particularly in the Bohr and Root effects, are generally well conserved, except in MN-Hbβ3. Six genes were mainly expressed during early life (MN-Hbα3-5, MN-Hbβ4–6), while the others were predominantly expressed at juvenile–adult stages. Adult fish expressed Hb genes at high levels in the head kidney and spleen; the main organs involved in blood formation. The Hb genes expressed in non-hematopoietic organs (intestine, gills, heart, brain, and liver) may facilitate oxygen homeostasis or be involved in antimicrobial defense. Stage- and tissue-specific gene expression patterns, together with the sequence features of the different Hb proteins, suggest a broad range of roles in European sea bass.

Ocean warming, eutrophication and consequent decrease in oxygen lead to smaller average fish size. Although such responses are well-known in an evolutionary context, involving multiple generations, it appears to be incompatible with current rapid environmental change. Rather, phenotypic plasticity could provide a means for marine fish to cope with rapid environmental changes. However, little is known about the mechanisms underlying plastic responses to environmental conditions that favour small phenotypes. Our aim was to investigate how and why European sea bass that had experienced a short episode of moderate hypoxia during their larval stage subsequently exhibited a growth depression at the juvenile stage compared to the control group. We examined whether energy was used to cover higher costs for maintenance, digestion or activity metabolisms, as a result of differing metabolic rate. The lower growth was not a consequence of lower feed intake. We measured several respirometry parameters and we only found a higher SDA (Specific Dynamic Action) duration and lower SDA amplitude in a fish phenotype with lower growth; this phenotype was also associated with a lower protein digestive capacity in the intestine. Our results contribute to the understanding of the observed decrease in growth in response to climate change. They demonstrate that the reduced growth of juvenile fishes as a consequence of an early-life hypoxia event was not due to a change of fish aerobic scope, but to a specific change in the efficiency of protein digestive functions. The question remains of whether this effect is epigenetic and could be reversible in the offspring.

Ocean warming, eutrophication and the consequent decrease in oxygen lead to smaller average fish size. Although such responses are well known in an evolutionary context, involving multiple generations, this appears to be incompatible with current rapid environmental change. Instead, phenotypic plasticity could provide a means for marine fish to cope with rapid environmental changes. However, little is known about the mechanisms underlying plastic responses to environmental conditions that favour small phenotypes. Our aim was to investigate how and why European sea bass that had experienced a short episode of moderate hypoxia during their larval stage subsequently exhibited a growth depression at the juvenile stage compared with the control group. We examined whether energy was used to cover higher costs for maintenance, digestion or activity metabolisms, as a result of differing metabolic rate. The lower growth was not a consequence of lower food intake. We measured several respirometry parameters and we only found a higher specific dynamic action (SDA) duration and lower SDA amplitude in a fish phenotype with lower growth; this phenotype was also associated with a lower protein digestive capacity in the intestine. Our results contribute to the understanding of the observed decrease in growth in response to climate change. They demonstrate that the reduced growth of juvenile fishes as a consequence of an early life hypoxia event was not due to a change of fish aerobic scope but to a specific change in the efficiency of protein digestive functions. The question remains of whether this effect is epigenetic and could be reversible in the offspring.

Background The better understanding of how intestinal microbiota interacts with fish health is one of the key to sustainable aquaculture development. The present experiment aimed at correlating active microbiota associated to intestinal mucosa with Specific Growth Rate (SGR) and Hypoxia Resistance Time (HRT) in European sea bass individuals submitted to different nutritional histories: the fish were fed either standard or unbalanced diets at first feeding, and then mixed before repeating the dietary challenge in a common garden approach at the juvenile stage. Results A diet deficient in essential fatty acids (LH) lowered both SGR and HRT in sea bass, especially when the deficiency was already applied at first feeding. A protein-deficient diet with high starch supply (HG) reduced SGR to a lesser extent than LH, but it did not affect HRT. In overall average, 94 % of pyrosequencing reads corresponded to Proteobacteria, and the differences in Operational Taxonomy Units (OTUs) composition were mildly significant between experimental groups, mainly due to high individual variability. The highest and the lowest Bray-Curtis indices of intra-group similarity were observed in the two groups fed standard starter diet, and then mixed before the final dietary challenge with fish already exposed to the nutritional deficiency at first feeding (0.60 and 0.42 with diets HG and LH, respectively). Most noticeably, the median percentage of Escherichia-Shigella OTU_1 was less in the group LH with standard starter diet. Disregarding the nutritional history of each individual, strong correlation appeared between (1) OTU richness and SGR, and (2) dominance index and HRT. The two physiological traits correlated also with the relative abundance of distinct OTUs (positive correlations: Pseudomonas sp. OTU_3 and Herbaspirillum sp. OTU_10 with SGR, Paracoccus sp. OTU_4 and Vibrio sp. OTU_7 with HRT; negative correlation: Rhizobium sp. OTU_9 with HRT). Conclusions In sea bass, gut microbiota characteristics and physiological traits of individuals are linked together, interfering with nutritional history, and resulting in high variability among individual microbiota. Many samples and tank replicates seem necessary to further investigate the effect of experimental treatments on gut microbiota composition, and to test the hypothesis whether microbiotypes may be delineated in fish. Electronic supplementary material The online version of this article (doi:10.1186/s12866-016-0885-2) contains supplementary material, which is available to authorized users.

The quality of development in intensive or mesocosm hatchery-reared Dicentrarchus labrax larvae was investigated using physiological indicators assessing ontogeny. Larvae were reared in intensive (120 L tanks) and in mesocosm systems (20 m(3) enclosures) with the same feeding sequence, excluding the wild zooplankton naturally available in mesocosms. Faster growth was recorded since early development [16 day after hatching (DAH)] in the mesocosm. Maturation of the digestive system also occurred earlier as indicated by the higher amylase secretion ratios, the intestinal maturation index (alkaline phosphatase/leucine-alanine peptidase and aminopeptidase-N/leucine-alanine peptidase ratios) and the more developed intestinal epithelium at 23 DAH. Nevertheless, the delay in digestive maturation in the intensive system seemed retrieved within few days. In both the groups, the number of vertebrae ranged between 24 and 26, with the dominant class being 25 vertebrae. However, the distributions differed between treatments for meristic characteristics, ossification stages and incidence of malformation types. Loss of a vertebra was more frequent in the intensive system, while the appearance of an additional vertebra was more frequent in the mesocosm. Ossification at 37 DAH was also more advanced in the mesocosm in addition to a lesser rate and severity of skeletal malformations. It is suggested that the early nutritional contribution of mesocosm wild zooplankton, yet at densities of 0.2-0.7 prey mL(-1), had key effects on larvae development since the early stages.

International audience; The influence of dietary vitamins on growth, survival, and morphogenesis was evaluated until day 38 of posthatching life in European sea bass larvae (Dicentrarchus labrax). A standard vitamin mix (VM), at double the concentration of the U. S. National Research Council's recommendations, was incorporated into larval feeds at 0.5%, 1.5%, 2.5%, 4.0%, and 8.0% to give treatments VM 0.5, VM 1.5, VM 2.5, VM 4.0, and VM 8.0, respectively. The group fed the VM 0.5 diet all died before day 30. At day 38, the larvae group fed VM 1.5 had 33% survival, while the other groups, with higher vitamin levels, showed at least 50% survival. The higher the percentage VM in the diet, the lower the percentage of column deformities. High dietary vitamin levels positively influenced the formation of mineralized bone in larvae: the higher the dietary vitamin level, the higher the ossification status. In the larvae group fed at the highest vitamin levels, we observed a temporal sequence of coordinated growth factor expression, in which the expression of bone morphometric protein (BMP-4) preceded the expression of IGF-1, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). In groups fed lower proportions of vitamins, elevated proliferator peroxisome-activated receptors (PPAR-gamma) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-gamma transcripts in larvae-fed diets with a low VM content converted some osteoblasts into adipocytes during the first two weeks of life. This loss of osteoblasts is likely to have caused skeletal deformities.

A study was designed to evaluate the maximum level of substitution of fish meal in diets for turbot when a mixture of feedstuffs of plant origin was used and when the amino acid profile was adjusted to reflect amino acid profile of a reference fish meal based diet. Five diets were formulated: a reference diet (FM40) containing 40% fish meal and four other diets (FM30, FM20, FM10 and FM0) in which protein from fish meal was substituted by protein from lupin, corn gluten and wheat gluten meal. Amino acids profile of each diet was balanced by addition of crystalline amino acids. Turbot, initially weighing 26 g were fed these diets for 12 weeks and growth parameters were recorded. Protein (96%), energy (83%) and dry matter (73%) digestibility were very high in all diets tested. Feed intake was significantly decreased by the incorporation of plant protein in diets (from 10.2 g/kg ABW/day to 8.2 g/kg ABW/day in fish fed diets FM40 and FM0, respectively), growth rate was only affected in fish fed diets FM10 and FM0 (respectively, 2.2 and 1.9%/day against an average of 2.4%/day for the other treatments) and no effect on feed utilisation was observed. The whole body composition of fish and the nitrogen retention were significantly negatively affected when dietary fish meal incorporation was equal or less than 20% diet. Activities of alanine amino transferase (ALAT) were significantly increased by the dietary incorporation of plant protein. These results suggest that a sizeable amount of fish meal can be replaced by plant feedstuffs in diets of turbot when an adequate mixture of plant feedstuffs along with amino acid supplementation are used.

The aim of the study was to evaluate the effects of dietary arginine (Arg) supplementation to either a plant protein-based diet or a fish meal-based diet on nitrogen (N) utilisation and ureogenesis in turbot and rainbow trout. Juvenile turbot (7.4 g) and rainbow trout (9.3 g) were fed for 12 weeks two types of diets (plant protein-based (PM) and fish meal-based (FM)) containing different levels of Arg (1.6%, 3% and 4% diet for PM diets and, 3% and 4% for FM diets). Besides, measurement of growth parameters and protein utilisation, ammonia and urea excretion rates were monitored. Plasma ammonia and urea concentrations and activities of selected enzymes of ornithine urea cycle (carbamoyl phosphate synthetase III, ornithine carbamoyltransferase and arginase) were measured. Both species fed PM-based diets had reduced growth performance compared to fish fed FM-based diets. Amino acid imbalance of the PM-based diets had a significant effect on plasma ammonia levels and ammonia excretion. Dietary Arg supplementation did not lead to any improvement in N utilisation or on ammoniogenesis. In both species, there was a linear relationship between dietary Arg and urea excretion. Our data confirm that ornithine urea cycle is incomplete in the liver and that argininolysis plays a major role in ureogenesis in both species.

Since European sea bass (Dicentrarchus labrax) larvae occurred in coastal and estuarine waters at early life stages, they are likely to be exposed to reduced dissolved oxygen waters at a sensitive developmental stage. However, the effects of hypoxia at larval stage, which depend in part on fish species, remain very poorly documented in European sea bass. In the present study, the impacts of an experimental exposure to a chronic moderate hypoxia (40 % air saturation) between 30 and 38 days post-hatching on the physiological and developmental traits of European sea bass larvae were assessed. This study was based on the investigation of survival and growth rates, parameters related to energy metabolism [Citrate Synthase (CS) and Cytochrome-c Oxidase (COX) activities], and biological indicators of the maturation of digestive function [pancreatic (trypsin, amylase) and intestinal (Alkaline Phosphatase "AP" and Aminopeptidase-N "N-LAP") enzymes activities]. While condition of hypoxia exposure did not induce any significant mortality event, lower growth rate as well as CS/COX activity ratio was observed in the Hypoxia Treatment group. In parallel, intestinal enzyme activities were also lower under hypoxia. Altogether, the present data suggest that sea bass larvae cope with moderate hypoxia by (1) reducing processes that are costly in energy and (2) regulating mitochondria functions in order to respond to energy-demand conditions. Both these effects are associated with a delay in the maturation of the digestive function.

Recent studies indicate that urea excretion is responsive to protein intake and that turbot, Psetta maxima, appear to differ from other species by their urea excretion pattern and levels. This study was undertaken to evaluate the influence of dietary nitrogen and arginine on ureagenesis and excretion in turbot. Juvenile turbot (29 g) were fed semi-purified diets containing graded levels of nitrogen (0–8% dry matter) and arginine (0–3% dry matter) for 6 weeks. Growth data showed that turbot have high dietary nitrogen (123 mg/kg metabolic body weight/day) and very low dietary arginine (9.3 mg/kg metabolic body weight/day) requirements for maintenance. Requirements for unit body protein accretion were 0.31 g and 0.15 g for nitrogen and arginine respectively. Post-prandial plasma urea levels and urea excretion rates showed that urea production was significantly (P

We evaluated the influence of dietary nucleic acid (NA) supplied either as an RNA extract (RNA) or as brewer's yeast (BY) on nitrogen (N) utilisation, N excretion and ureogenesis in a freshwater teleost, the rainbow trout (Oncorhynchus mykiss) and a marine teleost, the turbot (Psetta maxima). Five diets containing two levels of NA or BY were formulated for each species, and fed to juvenile rainbow trout (initial body weight (IBW): 21.7 g) and turbot (IBW: 11.8 g) over 8–10 weeks. Besides growth and N utilisation, we monitored total ammonia-N and urea-N excretion rates and measured the activities of selected enzymes (glutamate dehydrogenase, ornithine carbamoyltransferase, arginase and uricase). There was no clear N sparing effect of dietary NA or BY supplementations in either species. Feeding diets containing the RNA extract led to an almost two-fold increase in postprandial plasma urea-N and uric acid concentrations and in urea-N excretion rates. Glutamate dehydrogenase and arginase activities were decreased in fish fed NA supplemented diets. Uricase activities were inversely related to dietary NA levels. Data on N excretion and enzyme activities clearly suggest that ureogenesis is influenced by dietary NA in both species.

The incorporation of various bulk agents by substitution of an equivalent amount of the basal mixture was studied in terms of protein digestibility, growth performance and body composition in European seabass (Dicentrarchus labrax) juveniles. During the growth trial, triplicate groups of 40 seabass (mean initial weight: 7.0 g) were grown in seawater (salinity: 35; temperature: 18 degrees C) over 60 days. Fish were hand-fed, three times a day, one of seven experimental diets. Bulk agents tested at 10 or 20 % level of incorporation were silica, cellulose and a natural zeolite (chabamin). Feeding rates were adjusted in proportion to the percent dilution of the control diet without bulk incorporation. The incorporation of the bulk agents, at a 10 and 20 % level, did not affect protein digestibility or growth performance. Dietary bulk incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by the dietary nutrient dilution of the bulk-incorporated diets, rather than by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation profile of faeces and increased faecal egestion time.

International audience; The aim of this work was to investigate the catabolic process of three kinds of dietary carbohydrates in the gut of sea bass juveniles, with the possible contribution of the intestinal microbiota to the nutrition of the host, and the subsequent effects on intermediary metabolism. A first diet contained waxy maize (99% amylopectin), a highly digestible form of starch. A second diet was less quickly digestible due to its high amylose content of resistant starch. Two other diets contained fibre instead of starch, either only cellulose as control, or also other non-starch polysaccharides brought by lupin meal. The effect of the diets on the host confirmed previous results, with the stimulation of glucose storage in the liver in sea bass fed the starchy diets, which caused a significant increase in liver weight, while lupin meal caused an increase in visceral mass. Glycaemia was higher 7 ± 1 h after the last meal in the group fed resistant starch, compared to the other dietary groups, while the fast digestion of waxy maize resulted already in hypertriglyceridemia, possibly due to hepatic neolipogenesis. At the same sampling time, the activity of free amylase was reduced in the intestine of sea bass fed resistant starch, but maltase activity was stimulated in the brush border membranes of enterocytes in the same group, confirming thus the timely digestion of resistant starch. Hepatic mRNA transcripts indicated that glucose metabolism was oriented towards neoglucogenesis by the high-fibre diets, and towards glucose storage by the starchy diets, especially with waxy maize. The diet influenced both faecal and mucosal microbiota, though in different ways, likely due to the interaction with the host. Lupin meal seemed potentially interesting as a source of prebiotic polysaccharides, by modifying the balance between Vibrio spp. and Clostridium sp. Both forms of starch were also partly metabolised by microbiota, resulting in an increased concentration of acetate in the faeces.

The aim of this study was to determine whether mortality observed during the larval development of reared bluefin tuna (Thunnus thynnus) could be related to improper expression profiles of key genes involved in digestive or anti-oxidant response capabilities. Tuna larvae were sampled at hatching, 2, 5, 10, 15 and 20 dph (days post hatching) for the relative quantification of transcripts encoded by genes involved in digestive (trypsinogen 1 [TRYP1], alpha-amylase [AMY], aminopeptidase N [ANPEP]) and antioxidant (catalase 32 [CAT]) functions. The levels of expression of ANPEP related to the development and maturation of intestinal function increased from 5 to 20 dph. Furthermore, AMY and TRYP1 genes which are pancreatic enzymes implicated in carbohydrate and peptide digestions exhibit a typical peak of expression at 5 and 15 dph respectively. The antioxidant enzyme, CAT, exhibited higher mRNA levels during the first stage of larval development. In conclusion, our investigation indicates that the expression of genes involved in digestive and antioxidant physiological processes followed typical patterns which could not explain high mortality rate observed during the first stage of larval development, SI

Resume Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12OC under the same conditions beforc transfer of brown trout to sea water, in order to compare nitrogen utilisation in the two species. Apparent protein digestibility (ADC), nitrogen (ammonia and urea) excretion, protein productive value (PPV) and actual observed nitrogen mass balance were determined. Rainbow trout raised in fresh water had a higher growth rate (1.1 vs 0.8Yb.d-'), better food conversion ratio (0.7 vs 1.0), better ADC (91 vs 85%) and PPV (45 vs 35%) and lower ammonia excretion rates than brown trout reared in fresh water. Transfemng brown trout to sea water induced lower PPV (30%) and ammonia and urea excretion. Salinity did not rnodify metabolic efficiency in brown trout. Fat content was higher in brown trout (7.7-8.9% ww) than in rainbow trout (5.7-7.6% ww). Nitrogen mass balance indicated that compounds other than arnmonia and urea were produced in higher quantities by seawater brown trout. Behaviour, less domestication and specific ability to utilise protein could explain the differences between the two species.

International audience; An individual's environmental history may have delayed effects on its physiology and life history at later stages in life because of irreversible plastic responses of early ontogenesis to environmental conditions. We chose a marine fish, the common sole, as a model species to study these effects, because it inhabits shallow marine areas highly exposed to environmental changes. We tested whether temperature and trophic conditions experienced during the larval stage had delayed effects on life-history traits and resistance to hypoxia at the juvenile stage. We thus examined the combined effect of global warming and hypoxia in coastal waters, which are potential stressors to many estuarine and coastal marine fishes. Elevated temperature and better trophic conditions had a positive effect on larval growth and developmental rates; warmer larval temperature had a delayed positive effect on body mass and resistance to hypoxia at the juvenile stage. The latter suggests a lower oxygen demand of individuals that had experienced elevated temperatures during larval stages. We hypothesize that an irreversible plastic response to temperature occurred during early ontogeny that allowed adaptive regulation of metabolic rates and/or oxygen demand with long-lasting effects. These results could deeply affect predictions about impacts of global warming and eutrophication on marine organisms.

Three species of marine fish, sea bass, sea bream and turbot, and two salmonids, rainbow trout and brown trout, were raised under similar feeding and environmental conditions in order to compare their nitrogen utilisation. Apparent digestibility of protein, ammonia and urea excretion patterns, plasma ammonia and urea concentrations and liver arginase activities were measured. No differences in protein digestibility were noticed among the five species. Ammonia and urea losses were quantitatively similar in all species, except in turbot, in which ammonia production was significantly lower. Ammonia excretion patterns were linked to ingested nitrogen and showed no inter-species differences. Conversely, urea excretion patterns were specific in turbot and sea bream. Plasma urea levels were higher in marine fish than in salmonids, with the highest values being reached in turbot. Some specificity with regard to liver arginase was also detected in the turbot. Turbot demonstrated some metabolic characteristics that could be connected with its elevated position in the phylogeny of fish.

Laboratory experiments on juvenile turbot. Scophthalmus maximus (L.), were carried out under controlled temperature (12°C) and feeding regimes in a flow-through system. Monitoring of total ammonia nitrogen (TAN) and urea nitrogen (Urea-N) was performed through continuous sampling of the effluent sea water. The effects of ingested nitrogen levels on TAN and Urea-N daily and hourly excretion rates were studied. Strong relationships were found between ingested nitrogen, and both TAN and Urea-N excretion for both daily and hourly maximum excretion rates. Turbot showed a low metabolic activity, confirmed by low excretion levels. Daily patterns for TAN and Urea-N production were different, suggesting specific physiological phenomenon for urea excretion mechanisms. The question of whether turbot are partly ureotelic or ureogenic is underlined.

The influence of dietary ascorbic acid (AA) on growth and morphogenesis during the larval development of European sea bass ( Dicentrarchus labrax ) was evaluated until 45 days post hatching. Diets incorporated 0, 5, 15, 30, 50 or 400 mg AA per kg diet to give AA-0, AA-5, AA-15, AA-30, AA-50 and AA-400 dietary treatments, respectively. Dietary AA levels lower than 15 mg/kg reduced larval growth and survival was affected in specimens fed diets devoid of AA. Globally, disruption of the expression of genes involved in AA and calcium absorption in the intestine (SVCT-1, TRPV-6), skeletogenesis (BMP-4, IGF-1, RARγ) and bone mineralization (VDRβ, osteocalcin) were observed in groups fed doses lower and higher than 50 mg AA/kg diet. Such disturbances detected at molecular level were associated with disruptions of the ossification process and the appearance of skeletal abnormalities.

International audience; The influence of dietary vitamin D-3 (VD3) on survival, growth and morphogenesis during the larval development of European sea bass (Dicentrarchus labrax) was evaluated until 45 days post hatching. Diets contained 4% of the standard vitamin mix (VM) recommended by the National Research Council (NRC) and incorporated 0, 19.2, 38.4, or 140 IU of VD3 per gram of diet to give VD-0, VD-1, VD-2 and VD-3 dietary treatments, respectively. The present study revealed for the first time an impact of dietary VD3 on the sea bass digestive system ontogenesis that consequently conditioned the ossification process and morphogenesis. All dietary VD3 levels were in the "adequate range" based on larval survival. Nevertheless, growth, intestinal maturation and ossification at the end of the larval stage were harmed by the minimum dose of VD3 tested and resulted in the appearance of malformations. VD-2 and VD-3 groups showed satisfactory growth and ossification levels at the end of the larval period. However, results of enzymatic activity and expression of genes involved in the VD3 pathway (bone morphogenetic protein 4, osteocalcin, vitamin D receptors and transient receptor potential cation channel-subfamily V. member 6-) gave evidence of complications during the ossification process as revealed by the high percentage of deformed larvae. A VD3 level of 19.2 IU/g diet appeared necessary to obtain harmonious larval morphogenesis. (C) 2009 Elsevier B.V. All rights reserved.

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 degrees C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %), Orthophosphate excretion, ranging 7-20 mg phosphorus per kg wet weight per day, represented 10-20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (75 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for., Des truites communes et des truites arc-en-ciel ont été élevées à 12 °C dans des conditions strictement identiques, avant le transfert des truites communes en eau de mer, dans le but de comparer l'utilisation du phosphore chez les deux espèces. La disponibilité apparente de phosphore, l'excrétion d'orthophosphate par les poissons, et l'accrétion de phosphore chez ces poissons ont été estimées par mesure directe. Ainsi, les réels bilans de masse ont pu être construits. Les truites arc-en-ciel élevées en eau douce présentent un meilleur coefficient de rétention du phosphore (maximum 50 %) que les truites communes élevées en eau douce (maximum 45 %). Le transfert de la truite commune en eau de mer a entraîné une diminution de la rétention du phosphore (maximum 39 %). L'excrétion d'orthophosphate, de 7 à 20 mg de phosphore par kg de poids vif par jour, représente 10¿20 % du phosphore ingéré. La disponibilité du phosphore chez la truite commune était plus faible en eau de mer (65 %) qu'en eau douce (76 %). Le rapport entre les entrées et les sorties de phosphore du système d'élevage, compris entre 90 et 98 %, montre que l'estimation du bilan de masse est correcte.