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This study aimed to evaluate the effect of replacing fish meal by poultry by-product meal (PBM) in actual commercial standard diets for gilthead seabream juveniles on growth performance, diet digestibility, digestive function, intestinal microbiota, and provide an economic analysis of using PBM in practical diets. Six isoproteic and isolipidic diets were formulated including increasing levels (from 0 to 37.5%) of PBM in replacement of fish meal, corresponding to a fish meal protein replacement in the diets up to 83%. Each diet was randomly assigned to triplicate groups of fish (IBW 63 g) and the growth trial lasted 70 days. No differences between groups were observed on growth performance, voluntary feed intake, feed efficiency, nitrogen utilization, and whole-body composition. Digestive enzymes activity and the ADC of protein, phosphorus, and energy were also not affected by dietary treatment. Regarding gut microbiota, fish fed diet PBM22.5 showed higher species richness and diversity of digesta microbiota, but no differences between groups were observed in mucosa OTUs, richness, and diversity indices. The cost of diet formulation decreased with the dietary replacement of FM by PBM, highlighting the potential of poultry by-products inclusion in commercial diets. Overall, this study indicates that dietary FM could be replaced at least up to 83% with PBM in diets for gilthead seabream juveniles without affecting growth performance and feed utilization while improving the economic efficiency of these diets.

The aim of this study was to assess the effect of dietary taurine (Tau) in intermediary metabolism, oxidative status, and Tau biosynthesis capacity in European seabass juveniles. For that purpose, four diets (45% protein and 18% lipid) were formulated with increasing levels of Tau (0.2, 0.5, 0.7, and 1.2% of DM) and fed to triplicate groups of fish (IBW 55g) until apparent visual satiety for 10 weeks. Total bile acid content in the liver increased as dietary Tau supplementation increase, while the opposite occurred in the plasma. Plasma glucose, total cholesterol, HDL, and LDL cholesterol decreased, while total and indirect bilirubin increased with the increase of dietary Tau level. The activity of the key intermediary enzymes measured decreased with the increase of dietary Tau up to 0.7%. Regarding the antioxidant-related enzymes, dietary Tau supplementation decreased hepatic catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase activities with the maximum effects being observed as dietary Tau increased from 0.2 to 0.5%. Overall, there was a decreasing trend of hepatic lipid peroxidation with the increase of dietary Tau. This study is the first to demonstrate that in European seabass juveniles the capacity of expressing cysteine dioxygenase, an enzyme involved in the cysteine sulfinate pathway for Tau synthesis, although its expression was not affected by Tau levels in the diet. This study indicates that dietary Tau levels affect intermediary metabolism, namely carbohydrates and lipidic metabolism, and improve the antioxidant status of European seabass juveniles. Furthermore, although CDO expression was detected, European seabass seems unable to regulate its activity, these results supporting the essentiality of Tau for this species.

"Available online 3 August 2020", Oilseed cakes have potential for new applications as substrates for solid-state fermentation (SSF), to increase their nutritional value by increasing its polyunsaturated fatty acids (PUFAs) or protein content. In this sense, it was performed a screening of oilseed cakes to be used as substrates for the production of PUFAs by Mortierella alpina Peyronel MUM 9412. Of all by-products tested, linseed cake (LSC) was the oilseed cake that achieved the highest production of total PUFAs: 153.09 ± 2.25 mg/g. Overall, the PUFAs and protein contents of fermented LSC increased 33% and 11%, respectively. Further, supplementation of the rapeseed cake with linseed oil, prior to the SSF, proved to increase the PUFAs production in about 26%. This study demonstrated the potential of SSF for improving linseed and linseed cakes nutritional composition and the positive effect of linseed oil as inductor to improve the PUFAs production by M. alpina., José Manuel Salgado was supported by grant CEB/N2020 – INV/01/ 2016 from Project “BIOTECNORTE - Underpinning Biotechnology to foster the north of Portugal bioeconomy” (NORTE-01-0145-FEDER000004). This work was supported by the project “Development of innovative sustainable protein and omega-3 rich feedstuffs for aquafeeds, from local agro-industrial by-products”, reference POCI-01-0145- FEDER-030377, funded by European Regional Development Fund (ERDF). This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit and BioTecNorte operation (NORTE-01- 0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte., info:eu-repo/semantics/publishedVersion

Leptin, ghrelin, and insulin influence lipid metabolism and thus can directly affect adipose tissue characteristics, modulating the organoleptic quality of aquaculture fish. The present study explored gilthead seabream (Sparus aurata) cultured preadipocytes development, and the regulation of adipogenesis by those three hormones. Preadipocytes presented a fibroblast-like phenotype during the proliferation phase that changed to round-shaped with an enlarged cytoplasm filled with lipid droplets after complete differentiation, confirming the characteristics of mature adipocytes. peroxisome proliferator-activated receptor-γ (pparγ) expression was higher at the beginning of the culture, while fatty acid synthase and 3-hydroxyacyl-CoA dehydrogenase gradually increased with cell maturation. The expression of lipoprotein lipase-like, lysosomal acid lipase (lipa), fatty acid translocase/cluster of differentiation-36 (cd36), and leptin receptor (lepr) were not affected during cell culture development; and undetectable expression levels were observed for leptin. Concerning regulation, leptin inhibited lipid accumulation significantly reducing pparγ and cd36 gene expression, both in early differentiating and mature adipocytes, while ghrelin decreased the expression of pparγ in the early differentiating phase but did not reduce intracellular lipid content significantly. Additional insulin past the onset of adipogenesis did not affect lipid accumulation either. In conclusion, at present culture conditions leptin has an anti-adipogenic function in differentiating preadipocytes of gilthead seabream and continues exerting this role in mature adipocytes, while ghrelin and insulin do not seem to influence adipogenesis progression. A better understanding of leptin, ghrelin, and insulin impact on the adipogenic process could help in the prevention of fat accumulation, improving aquaculture fish production and quality.

A study was undertaken to evaluate the effects of supplementation of high soybean meal (SBM)/low fish meal (FM) based diets for white seabream ( Diplodus sargus ) juveniles with Natugrain® TS, a nonstarch carbohydrases (NSPase) enzyme complex. Four isoproteic (36% CP) and isolipidic (18% CL) diets were formulated in a 2 × 2 factorial design with FM/SBM levels and NSPase supplementation as factors. Diets included 15%FM/32%SBM or 5%FM/42%SBM, supplemented or not with 0.04% of Natugrain® TS. Twelve groups of 15 fish (IBW = 58 g) were fed each diet to near satiation for 10 weeks. The apparent digestibility coefficients of the diets were evaluated in a different trial. Reduction of dietary FM from 15 to 5% did not affect voluntary feed intake, growth performance, feed efficiency, whole body composition, apparent digestibility coefficients, distal intestine and liver histomorphology, and digestive enzyme activities. However, dietary NSPase supplementation greatly increased overall feed, protein, and energy utilization, and this effect was higher in the low than in the high FM diet. Whole-body protein and lipid content also increased with dietary NSPase supplementation, and nitrogen and energy fecal losses were reduced. Moreover, in the low FM diet NSPase supplementation promoted an increase of amylase and lipase activities but not of protease activity. Overall, results indicate that white seabream perform well with diets almost devoid of FM. Also, NSPase supplementation to high plant feedstuff diets improves feed and nutrient utilization efficiency, and contribute to a reduction of fecal waste production. Statement of relevance Dietary supplementation with carbohydrase complexes is a possible strategy to overcome some of the drawbacks of plant based feedstuffs diets for aquaculture species, enhancing nutrient availability and alleviate digestive disorder. White seabream accepted, grew and utilized almost non-FM diets, if dully supplemented with carbohydrases. Dietary carbohydrase supplementation considerably increased feed utilization efficiency, reducing environmental waste.

The aim of this study was to evaluate the effects of short-chain fructooligosaccharides (scFOS), xylooligosaccharides (XOS) and galactooligosaccharides (GOS) on immune and hepatic oxidative status, and gut morphology of white sea bream juveniles. Four diets were formulated: a control diet with fish meal (FM) and plant feedstuffs (PF) (30FM:70PF) and three test diets similar to the control but supplemented with 1% of scFOS, XOS or GOS. Dietary prebiotic incorporation did not affect total blood cell counts, hematocrit, hemoglobin, red blood indices or differential white blood cell counts. Fish fed GOS had lower ACH50 and nitric oxide than fish fed control diet. XOS enhanced immune status through the increase in alternative complement pathway (ACH50), lysozyme and total immunoglobulin. The higher activity of glucose 6-phosphate dehydrogenase in fish fed FOS compared to the other dietary groups was the only related antioxidant enzyme affected by prebiotics in the liver. GOS ameliorated the precocious adverse effects of PF based diet on gut histomorphology, as denoted by the lower incidence of histological alterations in fish fed GOS for 15 days. In conclusion, XOS and GOS at 1% might have potential to be used as prebiotics in white sea bream juveniles.

The effects of whole cereal meals on growth, nutrient digestibility, glycaemic response and gut morphology were studied in gilthead seabream juveniles. Groups of 30 fishes (in triplicate) were fed four isoproteic (47%) and isolipidic (16%) diets including 30% of wheat, corn, barley or rye meals. Growth performance was higher in fish fed the wheat diet than the rye diet. Feed efficiency and protein efficiency ratio were higher with the wheat and barley diets than in the other groups. There were no differences in apparent digestibility coefficients (ADCs) of dry matter, protein or lipids among diets. However, ADC of corn and barley starch was lower than that of wheat and rye starch. Average plasma glucose levels were lower in fish fed the barley diet. Plasma glucose peaked 10 h after feeding in all groups except the corn group which peaked 8 h after feeding. Shorter hyperglycaemia duration was observed in fish fed the corn diet (12 h) than the other diets (> 12 h). Gut morphology was similar in all groups irrespective of the sampling point. Based on growth performance, feed utilization efficiency, ADC of starch and glycaemic response we can conclude that wheat and barley are more efficiently used than corn or rye by gilthead seabream juveniles and thus are the preferential cereal sources to be used as plant feedstuffs in diets for this species. Statement of relevance Effective growth of fish at reduced costs.

A study was undertaken to evaluate dietary glutamine supplementation effects on gilthead sea bream performance, intestinal nutrient absorption capacity, hepatic and intestinal glutamine metabolism and oxidative status. For that purpose gilthead sea bream juveniles (mean weight 13.0g) were fed four isolipidic (18% lipid) and isonitrogenous (43% protein) diets supplemented with 0, 0.5, 1 and 2% glutamine for 6weeks. Fish performance, body composition and intestinal nutrient absorption capacity were not affected by dietary glutamine levels. Hepatic and intestinal glutaminase (GlNase), glutamine synthetase (GSase), alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase activities were also unaffected by dietary glutamine supplementation. In the intestine GlNase activity was higher and GSase/GlNase ratio was two-fold lower than in the liver, suggesting a higher use of glutamine for energy production by the intestine than by the liver. The liver showed higher catalase and glucose-6-phosphate dehydrogenase activities, while the intestine presented higher glutathione peroxidase and glutathione reductase activities and oxidised glutathione content, which seems to reveal a higher glutathione dependency of the intestinal antioxidant response. Total and reduced glutathione contents in liver and intestine and superoxide dismutase activity in the intestine were enhanced by dietary glutamine, though lipid peroxidation values were not affected. Overall, differences between liver and intestine glutamine metabolism and antioxidant response were identified and the potential of dietary glutamine supplementation to gilthead sea bream's antioxidant response was elucidated.

Vegetable oils (VO) are generally accepted as valuable alternatives to fish oils but are devoid of n-3 LC-PUFA (Long-Chain-Polyunsaturated Fatty Acids) and rich in C18-PUFA. Marine fish have limited capacity to express Δ6/Δ5 desaturases (FADS1 and FADS2) and elongases of very-long-chain fatty acids (Elovl), which severely limits their capacity to produce LC-PUFA from C18-PUFA. This study aimed to evaluate the effects of dietary essential fatty acids(EFA) ratios, arachidonic (ARA), eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids on growth performance, feed utilization, whole-body composition, hepatic and intestinal activity of key-enzymes of lipid and carbohydrate metabolism, and expression of lipid metabolism-related genes. Diets were formulated to include ARA/EPA/DHA ratios of 2.0/0.2/0.1 (Diet A); 1.0/0.4/0.4 (Diet B); 0/0.6/0.6 (Diet C); and 0/0.3/1.5 (Diet D) and were fed to triplicate groups of gilthead sea bream juveniles for 56 days. Dietary EFA ratios did not affect growth performance and whole-body composition. Nevertheless, feed and protein utilization were higher with diet B than diets C or D. Except for ARA, muscle EFA profile followed that of the diets. Plasma triglycerides were higher with diet B and C than A, and plasma cholesterol decreased in fish fed the higher DHA diet. Hepatic ELOVL5 and phospholipase A2 were upregulated in fish fed diet C compared to diet A. In the intestine, ELOVL5 levels were down-regulated in fish fed diet A and D compared to fish fed diet B. Overall, results showed that besides EPA and DHA, adequate dietary ARA level needs to be provided to optimize feed utilization efficiency of gilthead sea bream juveniles.

Insect meals are good candidates to replace fishmeal as new protein sources in aquafeeds. This study evaluated the effects of fishmeal replacement with different dietary inclusion levels of a partially defatted Tenebrio molitor (L.) larva meal (TM) on rainbow trout (Oncorhynchus mykiss Walbaum) growth, diet digestibility, and hepatic intermediary metabolism. A 154-day growth trial was performed with 252 rainbow trout (78.3 ± 6.24 g) randomly divided into twelve tanks and fed four experimental diets containing increasing levels of TM: 0% (TM0), 25% (TM25), 50% (TM50), and 100% (TM100) of fishmeal substitution, corresponding to TM dietary inclusion levels of 0%, 5%, 10%, and 20%, respectively. A digestibility trial was performed feeding 180 rainbow trout (94.6 ± 7.31 g) with the experimental diets used in the growth trial. The growth parameters were not affected by TM dietary inclusion. Regarding the evaluated apparent digestibility coefficients (ADC), only the ADC of crude protein was affected, showing the following trend: TM0 = TM25 &gt, TM50 &gt, TM100. The activities of key hepatic amino acid catabolic and lipogenic enzymes were not affected by the dietary composition. The results suggest that a partially defatted TM could totally replace fishmeal in commercial rainbow trout diets without negative effects on fish performance.

Made available in DSpace on 2018-11-26T17:48:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-03-10 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) The present study aimed to evaluate the effect of dietary linoleic acid to linolenic acid (LNA/ALA) ratio on growth performance, feed utilization, plasma metabolite profiles, and muscle and liver fatty acid profiles of juvenile tambaqui Colossoma macropomum. Six diets were formulated to contain incremental levels of corn oil (rich in LNA) from 0 to 7% at the expense of linseed oil (rich in ALA), resulting in dietary LNA/ALA ratios ranging from 3.1 to 26.9. A control diet including fish oil was also formulated. The trial lasted 49 days, and each diet was assigned to six groups of fish with an initial body weight of 43 g. At the end of the trial, dietary LNA/ALA ratio did not affect growth performance, feed utilization, and plasma metabolites profile, except for HDL that was lower in fish fed the 3.8 LNA/ALA diet than the 3.1 or 5.0 LNA/ALA diets. Whole-body protein content was lower in fish fed the control and 3.1 LNA/ALA diets. Composition of triglycerides, glucose and protein of liver and muscle was unaffected by dietary treatments. Eicosapentaeneoic acid (EPA, 20: 5n-3) plus docosahexaenoic acid, (DHA, 22: 6n-3) content of muscle decreased with the increase of LNA/ALA ratio. Fish fed 3.9-5.6 LNA/ALA diet showed the highest concentration of muscle ARA (arachidonic acid, 20: 4n-6) and EPA+ DHA among vegetable oil diets, though lower than that of fish fed the fish oil based diet. In conclusion, dietary LNA/ALA ratio should range between 3.9-5.6 to produce fillets with high EPA, DHA, and ARA contents, thus improving the nutritional quality of tambaqui fillets for human consumers. Univ Fed Lavras, UFLA, Dept Zootecnia, Lavras, MG, Brazil Univ Porto, Fac Ciencias, Dept Biol, Porto, Portugal Univ Estadual Paulista, Dept Zootecnia, Fac Ciencias Agr & Vet Jaboticabal, Jaboticabal, SP, Brazil Ctr Invest Marinha & Ambiental, CIIMAR, Terminal Cruzeiros, Matosinhos, Portugal Univ Estadual Paulista, Dept Zootecnia, Fac Ciencias Agr & Vet Jaboticabal, Jaboticabal, SP, Brazil CNPq: 140740/2013-9 CAPES: 99999.010687/2014-09 FAPEMIG: PPM 00227/12

The effect of a dietary incorporation of the seaweedsUlva lactucaandChondrus crispusas functional ingredients was evaluatedin gilthead seabream (Sparus aurata) juvenile growth, feed efficiency, muscle lipid composition, intermediary metabolism,oxidative status and gut histomorphology. Fish (15 g initial body weight) were fed with isoproteic (46%) and isolipidic (18%)diets with fish meal (FM) and plant feedstuffs (PF) (27:73 protein from FM:PF) as main protein sources (control diet). Three otherdiets were formulated similar to the control but including 5%U. lactuca,5%C. crispusor 2.5% of both algae (dietsUlva,Chondrusand Mix, respectively). Dietary incorporation ofUlvadid not affect growth performance (P> 0.05) while it leads tohigher muscleΣSFA (saturated fatty acids); and liver lipid peroxidation (LPO). Moreover, lower muscleΣPUFA (polyunsatu-rated fatty acids) and plasma glucose was observed. Dietary incorporation ofChondrusleads to lower growth; whole-body drymatter and lipid content; muscleΣPUFA andω3 fatty acids; and plasma glucose. In addition, higher muscleΣMUFA (mono-unsaturated fatty acids); and liver LPO was observed. Dietary incorporation of both algae (Mix) led to lower growth; whole-bodylipid content; muscleΣPUFA andω3 fatty acids; plasma glucose; and hepatic PK (pyruvate kinase) and HOAD (3-hydroxyacyl-CoA dehydrogenase). Furthermore, it leads to higher muscleΣSFA andΣMUFA; and liver LPO. Overall, no beneficial effects ofincluding the tested seaweeds in the diets was observed, while oxidative status was negatively affected in all dietary treatments., This work was supported by the StructuredR&D&I Project INNOVMAR (ref. NORTE-01-0145-FEDER-000035)within the research line INSEAFOOD, founded by the NorthernRegional Operational Programme (NORTE2020) through the EuropeanRegional Development Fund (ERDF). The Fundação para a Ciência e aTecnologia (FCT) and the FEDER, under programme PT2020 (ProjectUID/QUI/50006/2013) are also acknowledged for the financial funding.I.G., R.M. and A.C. were supported by FCT grants (SFRH/BPD/114959/2016, SFRH/BD/115870/2016 and SFRH/BPD/101354/2014, respec-tively). F.C. was a recipient of a grant within the Project ZEBRALGRE(PTDC/CVT-WEL/5207/2014).

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.

Corn distillers dried grains with solubles (DDGS) is a co-product of corn ethanol production which biological value is dependent on technological processes and so may be highly variable among production plants. Therefore, two digestibility trials were conducted to evaluate the apparent digestibility coefficients (ADCs) of nutrients and energy of two commercial sources of DDGS and their effects on digestive enzyme activities in European seabass and meagre juveniles. DDGS digestibility was determined based on the substitution of 30% of a reference diet (45% CP; 16% CL) by each test DDGS. ADCs of protein (92–98%), most amino acids (75–99%) and lipids (82–89%) were high while that of energy (58–68%) was low, reflecting the high indigestible fiber content of DDGS. ADCs of nutrients and energy of DDGS were similar in both species, except for some amino acids (lysine, arginine, histidine, isoleucine, tyrosine and aspartic acid) which were higher for seabass than for meagre. Independent of fish species, ADCs of protein and energy were higher in DDGS1 than in DDGS2, whereas ADCs of lipids and most amino acid were not affected by DDGS source. Digestive enzymes activities were species specific: protease activity was higher in meagre while lipase and amylase activities were higher in seabass. For both species, all digestive enzymes activities were higher in mid intestine than in anterior or distal intestine. Overall, it is concluded that corn DDGS is well digested and seems to have high potential for inclusion in diets for seabass and meagre juveniles.

The effects of short-chain fructooligosaccharides (scFOS) and xylooligosaccharides (XOS) on growth, feed utilization and liver activity of key enzymes of glycolytic, gluconeogenic, and lipogenic pathways were studied in European sea bass juveniles. This is the first study about the effect of prebiotics on fish glucose metabolism and few and contradictory studies are available about prebiotic effect on lipid metabolism. Fish were fed isoproteic (46%) and isolipidic (15%) diets based on fish meal (FM diets) or plant ingredients (PP diets; 30 FM:70 PP) as main protein sources. Four other diets were formulated similar to the control diets (PPC; FMC) but including 1% scFOS or 1% XOS (PPFOS, PPXOS, FMFOS and FMXOS diets). Growth performance was higher in fish fed PPXOS diet than PPC diet. No effect of dietary prebiotics on feed efficiency was noticed. Glucokinase activity was higher in fish fed FMFOS and FMXOS diets than FMC diet. Lipogenic enzyme activities (malic enzyme, fatty acid synthetase, glucose-6-phosphate dehydrogenase) were lower in fish fed diets including XOS than in the other groups. Glycolytic (glucokinase, pyruvate kinase) and lipogenic enzyme activities were higher, and gluconeogenic (fructose-1,6-bisphosphatase) enzyme activity was lower in fish fed FM diets than the PP diets. Overall, dietary XOS decreased lipogenesis, independently of dietary protein source, and improved growth performance in fish fed PP diets. In fish fed FM diets, XOS and scFOS increased glycolytic activity. XOS seemed to have good potential to be used as prebiotic in European sea bass.

Fish are usually exposed to farm operations that can activate the stress system, which in turn diverts energy from normal metabolic processes (i.e. growth or immune defence) to deliver it into the physiological systems activated to cope with stress. The main goal of this study was to assess the effect of high stocking densities on growth performance of Senegalese sole (Solea senegalensis) juveniles reared under intensive farming conditions. The impact of high densities on plasma cortisol and metabolites, humoral immune parameters and hepatic oxidative status was evaluated. Senegalese sole juveniles (45 ± 5 g average body weight) were stocked at three different initial densities (7, 17 and 24 kg m− 2) throughout a 60 days rearing period. Final stocking densities were 13, 31 and 40 kg m− 2 with no differences in terms of growth performance. Similar levels of plasma cortisol, circulating leucocytes and metabolites and humoral innate immune parameters suggest that stocking densities do not affect the hematological and biochemical status of Senegalese sole juveniles, at least under the current experimental conditions. Overall, this study presents the possibility for Senegalese sole on-growing at high stocking densities, strengthening the needs for its intensive commercial farming.

The gut microbiomes of fish play important roles in host development, digestion and health. Evidence suggests that abiotic factors, such as diet and rearing temperature, could affect fish gut microbiota. In this study, the effect of dietary short-chain fructooligosaccharides (scFOS) on turbot intestinal health, microbiota and digestive enzymes was investigated at two rearing temperatures: 15 and 20 °C. Four practical diets were supplemented with scFOS at 0, 5, 10 and 20 g kg−1. scFOS did not affect fish performance. PCR-DGGE did not show differences in bacterial profiles between dietary treatments; however, the number of operational taxonomic units, richness and diversity were higher at 20 °C. Enzyme activities in the foregut were not affected by rearing temperature, while in the hindgut, enzyme activities were higher at 15 °C. Total alkaline protease, α-amylase and lipase activities in the foregut were higher in fish fed 20 g kg−1 scFOS. Prebiotic supplementation had no effect on hindgut α-amylase activity, while lipase activity of fish reared at 20 °C was higher in fish fed diet with 5 g kg−1 scFOS. No differences were observed in intestinal morphology. This was the first study to simultaneously evaluate the effect of dietary prebiotic level and rearing temperature on fish intestinal microbiota and health.

To assess the effect of feeding frequency on the utilization of dietary starch by white sea bream juveniles, triplicate groups of fish were fed an experimental diet (400 g kg−1 protein, 140 g kg−1 lipids and 350 g kg−1 pregelatinized maize starch) to apparent visual satiation 2, 3 or 4 times a day for 63 days. Growth performance, feed utilization efficiency, glycaemia, cholesterolaemia, plasma triacylglycerides, liver lipids and glycogen content were unaffected by feeding frequency. α-Amylase activity increased from the pyloric caeca to the posterior intestine and was higher in fish fed twice a day than in fish fed 3 or 4 times a day. Hepatic glucokinase (GK) activity decreased with the increase in feeding frequencies, whereas fructose-1,6-bisphosphatase (FBPase) activity increased. Hepatic glucose-6-phosphate dehydrogenase and glutamate dehydrogenase activities were unaffected by feeding frequency. Overall, feeding frequency did not improve white sea bream dietary starch utilization. α-Amylase, GK and FBPase activities responded to dietary starch consumed at each meal, denoting a good metabolic adaptation of the fish to the feeding conditions.

This study was the first to investigate the effect of soy antinutrients, saponins and phytosterols, in on-growing sea bass. Seven diets were formulated: a control diet (fishmeal and fish oil based) and six diets containing 1 or 2 g kg−1 levels of soya saponins, 5 or 10 g kg−1 levels of phytosterols or a combination of 1 g kg−1 saponins + 5 g kg−1 phytosterols or 2 g kg−1 saponins + 10 g kg−1 phytosterols. After a 59 days feeding trial fish were weighed, faeces collected for digestibility studies and plasma sampled for cholesterol quantification. At day 15 and 59, distal intestine (DI) samples were collected for histological evaluation and quantification of maltase (Malt), alkaline phosphatase (AlP) and leucine aminopeptidase (LAP) activities. At day 59, DI was collected for gene expression of AlP, Malt and immune related genes. Antinutrients had no effect on fish performance, digestibility, plasma cholesterol levels and digestive enzymes activities and gene expression. Only mild morphological changes were present in groups fed high levels of saponins + phytosterols. Expression of immune related genes showed no differences between groups. Overall, on-growing sea bass showed high tolerance to dietary antinutrients up to the levels tested.

A 14 weeks growth trial was performed to estimate the protein requirement for growth and maintenance of zebra sea bream (Diplodus cervinus) juveniles. For that purpose, nine isolipidic diets were formulated to contain increasing protein levels (from 50 to 550 g kg−1) at the expense of carbohydrate. Each diet was assigned to duplicate groups of 20 fish, with an average body weight of 7.7 g. Feed efficiency improved with dietary protein up to 400 g kg−1, no further differences being noticed at higher protein levels. Fish fed the 50 g kg−1 protein diet lost weight during the trial. In the other groups, weight gain improved as dietary protein increased up to 350–400 g kg−1. Fish fed diets with 250 g kg−1 protein or lower had lower whole-body protein content than the other groups. A curvilinear-plateau model was used to adjust weight gain and protein gain (g kg ABW−1 day−1) to dietary protein levels. Based on that model, the optimum dietary protein requirement for maximum weight gain was estimated to be 437.6 g kg−1 and for maximum protein gain 461.9 g kg−1, corresponding to a protein intake of 7.63 g kg ABW−1 day−1. Protein requirement for maintenance was estimated to be 1.01 g kg ABW−1 day−1.

Summary This work aims to establish normal reference intervals for selected hemato-biochemical parameters, based on their potential clinical relevance, and which may contribute to evaluating the health, nutritional and welfare status of Senegalese sole (Solea senegalensis Kaup, 1858) juveniles. Thirty-one healthy Senegalese sole juveniles grown under intensive aquaculture conditions were used in the study. Based on the robust method with Box–Cox transformation data the established reference intervals for hematological parameters were: hematocrit 12–26%, hemoglobin 2.8–6 g dl−1, erythrocytes 90–97.0% total, leucocytes 4–10% total; erythrocyte indices and differential leucocytes counts were also evaluated. Reference intervals for biochemical parameters were (g dl−1) glucose 19–86 mg dl−1, total protein 2.6–6.3, albumin 1–2.34, globulins 1.8–4.1, lipids 0.7–1.3, triglycerides 0.3–1.8, total cholesterol 0.1–0.9 g dl−1, HDL-cholesterol 4–65 mg dl−1, LDL-cholesterol 7–532 mg dl−1, sodium 124–202 mmol L−1), potassium 1.1–4.6 mmol L−1, calcium 7.6–13.2 mg L−1, magnesium 1.8–4.8 mg L−1, inorganic phosphorus 3.4–9.5 mg L−1, alkaline phosphatase 93–598 U L−1, aspartate aminotransferase 118–605 U L−1, lactate dehydrogenase 8.7–782 U L−1, and creatine phosphokinase 31.5–552 U L−1. This data is expected to provide a valuable tool to monitor the stress, health and nutritional conditions of Senegalese sole juveniles under aquaculture production.

Plant ingredients contain antinutritional factors that may affect fish growth performance and health when included in their diets. The present work aimed at studying the effect of two soy purified antinutrients, saponins and phytosterols, on growth, intestinal morphology and immune response of on-growing sea bream. Fish were fed one of seven diets for 48 days: control diet (fishmeal and fish oil based) and six experimental diets containing low (0.1%) or high (0.2%) levels of soya saponins, low (0.5%) or high (1.0%) levels of phytosterols or a combination of 0.1% saponins +0.5% phytosterols or 0.2% saponins +1.0% phytosterols. At day 15 and at the end of the trial pyloric caeca (PC) and distal intestine (DI) samples were collected for histological evaluation. At the end of the trial plasma was sampled for cholesterol analysis and DI was sampled for gene expression of immune and functional genes. Saponins and phytosterols did not affect fish growth, feed utilisation or plasma cholesterol levels. Histologically only a mild increase in the number of eosinophilic granular cells in the PC after 15 and 48 days of feeding in fish fed 0.1% saponins and 0.5% phytosterols, respectively. Gene expression of immune related genes was not affected by the presence of dietary antinutrients. Sea bream in grow-out phase showed high tolerance for saponins and phytosterols either alone or in combination, thus indicating an ability to cope with dietary plant feedstuffs containing such antinutrients, at least within the concentration range used in the present study.

[EN] A feeding trial was carried out to assess the effect of partially replacing fish meal (FM) by Black soldier fly pre-pupae meal (HM) in diets for European seabass Dicentrarchus labrax juveniles. A FM-based diet was used as a control and three other diets were formulated to include 6.5%, 13%, and 19.5% of HM, replacing 15%, 30% and 45% of FM respectively. Each diet was fed to triplicate groups of fish (initial weight: 50 g) for 62 days. At the end of the trial, there were no differences among groups in growth performance or feed utilization. Plasma metabolic profiles also remained unaffected, except that plasma cholesterol was reduced with dietary HM inclusion. The apparent digestibility coefficients (ADC) of protein, lipids, dry matter, organic matter, and energy were generally high, and not affected by the dietary treatment. The ADC of arginine, histidine, and valine were higher in HM diets when compared to the control. Amylase and protease activities were not affected by dietary HM, while lipase activity was lower in HM 6.5 diets than in the control and HM 19.5 diets. In conclusion, up to 19.5% of HM, corresponding to 22.5% of total dietary protein, may successfully replace FM in diets for juvenile European seabass, without adverse effects on growth performance, feed utilization or digestibility., This research was partially supported by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT - Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the programme PT2020. We would like to express our thanks to P. Correia for assistance during the growth and digestibility trial. Magalhaes, R. was supported by a VEGICOR-AMINOAQUA project grant (ref. 31-03-05-FEP-43)

The effect of short-chain fructooligosaccharides (scFOS) incorporation on growth, feed utilization, body composition, plasmatic metabolites and selected liver enzyme activities of turbot juveniles reared at winter (15 °C) and summer (20 °C) temperatures was studied. Four comparable diets were formulated to contain circa 50 : 50 fish meal and plant ingredients as protein sources. Experimental diets included increasing levels of scFOS (0, 5, 10 and 20 g kg−1). Final weight was higher at 20 °C, but thermal growth unit, feed efficiency, nitrogen and energy retention were better at 15 °C. scFOS supplementation did not affect fish growth performance. Fish reared at 15 °C had higher liver glycogen, visceral and hepatosomatic indices. Liver lipids, plasma triglycerides, total lipids, cholesterol HDL and LDL were higher in turbot reared at 20 °C. Malic enzyme, fatty acid synthetase, alanine aminotransferase and glutamate dehydrogenase activities were higher in fish reared at 15 °C. Malic enzyme was lower in turbot fed with 20 g kg−1 scFOS compared to control diet; however, fatty acid synthetase presented an increasing trend as dietary scFOS increased up to 10 g kg−1. Glutamate dehydrogenase activity was higher in fish fed the control diet. Results seem to indicate no benefits of scFOS incorporation to diets on growth performance of turbot.

The use of plant ingredients in aquafeeds for piscivorous fish species is a reality that exposes fish to a number of antinutritional factors present in plants. The present study is the first to evaluate the effect of two purified antinutrients, saponins and phytosterols, in sea bream juveniles. For that purpose, seven diets were formulated: a control diet (fishmeal and fish oil based) and six experimental diets containing low (1 g kg− 1, SapL) or high (2 g kg− 1, SapH) levels of purified soya saponins, low (5 g kg− 1, PhytL) or high (10 g kg− 1, PhytH) levels of purified phytosterols or a combination of 1 g kg− 1 saponins + 5 g kg− 1 phytosterols (SapPhytL) or 2 g kg− 1 saponins + 10 g kg− 1 phytosterols (SapPhytH). Fish were fed for 48 days in order to evaluate growth performance, feed utilization, plasma cholesterol, and gut health as assessed by histomorphological evaluation and gene expression profiling of immune and functional markers. Fish fed the diets PhytH, SapPhytL and SapPhytH showed better feed utilization and PhytH and SapPhytH showed higher protein utilization than the other groups, although this was not reflected in improved growth performance. Histomorphological analysis of the distal intestine revealed increased variation in supranuclear vacuole sizes after 48 days of feeding diets SapH, SapPhytL and SapPhytH and increased number of intraepithelial leukocytes in response to all dietary treatments except SapL and SapPhytL. Although juvenile sea bream growth was not affected by dietary inclusion of saponins and phytosterols, the results indicated some disturbances of the intestinal mucosal structure that could compromise function and/or protection from potential dietary antigens or opportunistic pathogens.

This study was carried out to establish biochemical parameters with potential diagnostic value to assess the nutritional status of healthy seabass. For that purpose, triplicate groups of seabass juveniles were submitted to different feeding protocols: fed for 14 days; fed for 7 days followed by 7 days of fasting or fasted for 14 days. At the end of the trial, body, liver and viscera were randomly sampled for proximate composition analysis. Blood was also collected and the following plasma parameters were analyzed by standard clinical methods: glucose; cholesterol; triglycerides; protein; inorganic phosphorus; calcium; magnesium; alkaline phosphatase (ALP); aspartate aminotransferase; lactate dehydrogenase; creatine phosphokinase and lipase. No major effect of feed deprivation on body composition, visceral index, perivisceral and hepatic lipid content were observed, whereas hepatosomatic index and hepatic glycogen were reduced. Previous feeding conditions strongly influenced the plasma parameters in seabass. Comparatively to the fed group, plasma glucose, cholesterol and calcium levels were reduced after 2 weeks of fasting while plasma triglycerides, protein, inorganic phosphorus and ALP attained minimum levels after 1 week of fasting. Overall, enzymatic activity parameters showed higher variability than biochemistry parameters. In conclusion, during short-term starvation (

This study aimed to elucidate the effects of two soy antinutrients, saponins and phytosterols, on growth, intestinal health and function of European sea bass juveniles. Seven fishmeal-based diets were formulated: a control diet without antinutrients and six experimental diets containing low or high levels of soyasaponins (SapL and SapH, respectively), low or high levels of phytosterols (PhytL and PhytH, respectively) and low or high levels of soyasaponins + phytosterols (SapPhytL and SapPhytH, respectively). A feeding trial was conducted for 59 days after which blood was collected for plasmatic cholesterol quantification and intestinal samples were collected for histology, digestive enzymes activity and gene expression analysis. Histology was also performed at day 15. PhytL resulted in high distal intestine (DI) relative weight and decreased plasma cholesterol, while PhytH caused inflammatory changes in the DI. SapH depressed maltase and alkaline phosphatase activity in DI and the histological evaluation indicated some inflammatory changes. The SapPhytH resulted in decreased maltase activity in the DI and indications of inflammatory changes that were supported by the results on gene expression profiles. The antinutrients tested did not compromise growth, however, caused some gastrointestinal disturbance that may affect fish in the long term.

The supplementation effect of a high plant protein diet with methionine and taurine on nutrient digestibility, digestive enzymes activity, plasma and intestine bile acid content, and plasma metabolites was assessed in meagre juveniles. A control (CT) diet was formulated with 42% crude protein and 18% lipids, and including only 10% fishmeal, corresponding to 18% of the dietary protein level. Three other diets were formulated similar to the control but supplemented with 0.26% methionine (MET), 1.0% taurine (TAU), or 0.26% Met plus 1.0% Tau (MET+TAU), in a 2 × 2 factorial design. Final dietary Met levels were 0.75 and 1.0%, and Tau levels were 0.10 and 1.20%. Diets were fed to triplicate groups of 103 ± 21.2 g fish, twice a day, to apparent satiation. Fish were assembled in fiberglass tanks (60 L of water capacity), each one with feces settling column. Dietary Met supplementation increased apparent digestibility of dry matter, protein, lipids, and energy while dietary Tau supplementation increased lipids digestibility. Lipase activity was not affected by dietary methionine level, but it was higher in fish fed the taurine supplemented diet at the higher methionine level. Proteases and amylases activities were not affected by diet composition. Total bile acid in plasma and anterior intestine increased with dietary Tau supplementation. Dietary Tau supplementation also increased plasmatic levels of cholesterol, total proteins, and triglycerides. Overall, results of this study indicate that dietary methionine supplementation improved diet digestibility and that dietary taurine supplementation improved lipid digestibility and positively affected lipid metabolism in meagre.

Characterization of the major classes of digestive enzymes (amylase, protease and lipase) in the pyloric caeca and intestine of an omnivorous, white seabream (Diplodus sargus) and a carnivorous, meagre (Argyrosomus regius) fish species was assessed in response to dietary brewer's spent yeast (BSY, Saccharomyces pastorianus) supplementation. For that purpose, three isonitrogenous (50%) and isolipidic (12%) diets were formulated: unsupplemented (control) or supplemented with BSY at 1 or 2%. White seabream exhibited lower proteolytic but higher amylase and lipase activities than meagre. In white seabream, BSY administration enhanced amylase and protease activities in the pyloric caeca and the intestine and lipase activity in the pyloric caeca, while in meagre, improvement on amylase activity in the pyloric caeca was observed with the 2% BSY diet. The results of the current study indicate that white seabream has higher ability to digest non-protein energy sources than meagre and that diet supplementation with BSY improved digestive capacities in both species.

The objective of this study was to evaluate the potential of free amino acids to replace protein-bound amino acids in diets for Solea senegalensis juveniles. For this purpose, fish with 4.26 g mean initial weight were fed during 55 days with diets containing 500 g kg−1 protein and 100 g kg−1 lipid, based on fish meal and fish oil as main protein and lipid sources (control diet), or diets where 20%, 35% and 50% of fish meal were replaced by crystalline amino acids, using L-lysine HCl as lysine source. To access the efficiency of the crystalline lysine source, another diet was formulated with 35% fish meal replacement but using L-lysine sulphate instead of L-lysine HCl as lysine source. Overall, growth performance, feed utilization, nutrient retention, whole-body and amino acid composition did not show significant differences among groups. In conclusion, up to 50% protein-bound amino acids can be replaced by crystalline amino acids in diets for Senegalese sole juveniles without negative effects in fish performance. Additionally, it was shown that L-lysine sulphate and L-lysine-HCl may be used interchangeably by Senegalese sole juveniles, with the potential economic benefits involved.

The effects of dietary short chain fructooligosaccharides (scFOS) incorporation on hematology, fish immune status, gut microbiota composition, digestive enzymes activities, and gut morphology, was evaluated in gilthead sea bream (Sparus aurata) juveniles reared at 18 °C and 25 °C. For that purpose, fish with 32 g were fed diets including 0, 0.1, 0.25 and 0.5% scFOS during 8 weeks. Overall, scFOS had only minor effects on gilthead sea bream immune status. Lymphocytes decreased in fish fed the 0.1% scFOS diet. Fish fed the 0.5% scFOS diet presented increased nitric oxide (NO) production, while total immunoglobulins (Ig) dropped in those fish, but only in the ones reared at 25 °C. Red blood cells, hemoglobin, bactericidal activity and NO were higher at 25 °C, whereas total white blood cells, circulating thrombocytes, monocytes and neutrophils were higher at 18 °C. In fish fed scFOS, lymphocytes were higher at 18 °C. Total Ig were also higher at 18 °C but only in fish fed 0.1% and 0.5% scFOS diets. No differences in gut bacterial profiles were detected by PCR-DGGE (polymerase chain reaction denaturing gradient gel electrophoresis) between dietary treatments. However, group's similarity was higher at 25 °C. Digestive enzymes activities were higher at 25 °C but were unaffected by prebiotics incorporation. Gut morphology was also unaffected by dietary prebiotic incorporation. Overall, gut microbiota composition, digestive enzymes activities and immunity parameters were affected by rearing temperature whereas dietary scFOS incorporation had only minor effects on these parameters. In conclusion, at the tested levels scFOS does not seem worthy of including it in gilthead sea bream juveniles diets., This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE - Operational Competitiveness Programme and national funds through FCT Foundation for Science and Technology, under the projects "PEst-C/MAR/LA0015/2013 and UID/Multi/04423/2013". I. Guerreiro, P. Enes, A. Couto and B. Costas were supported by grants (SFRH/BD/76139/2011; BPD/39688/2007, BD/47495/2008 and BPD/77210/2011, respectively) from FCT, Portugal. C. Serra and A. Salvador were recipient of grants within the Project AQUAIMPROV (reference NORTE-07-0124-FEDER-000038) and Project BioEnv (REF. NORTE-07-0124-FEDER-000048), co-financed by the North Portugal Regional Operational Programme (ON.2 - O Novo Norte). We would like to express our thanks to Pedro Correia for the assistance during the growth trial. Authors would also thank to Jefo Species-specific additives France, for providing the prebiotic.

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.

Summary The aim of this study was to assess plasma biochemistry parameters with the potential of being used as indicators of the nutritional status for healthy gilthead seabream juveniles. Triplicate groups of 18 seabream (body weight of 58 g) were kept unfed for 24 h, 7 or 14 days. Nine fish per treatment were then sampled randomly for blood collection and the following parameters analyzed in the plasma using standard clinical methods: glucose; protein; triglycerides; cholesterol; calcium; magnesium; inorganic phosphorus; alkaline phosphatase (ALP); aspartate aminotransferase (AST); lactate dehydrogenase (LDH); gamma-glutamyl transferase (GGT); creatine phosphokinase (CPK); and lipase. Biochemical parameters showed lower variability among individuals than did enzymatic parameters. Plasma glucose, protein, cholesterol, calcium and inorganic phosphorus levels were inversely related to the duration of starvation. On the contrary, plasma triglycerides decreased significantly during the first week of starvation and remained stable in the second week. Plasma ALP, AST and LDH decreased significantly after 1 week of starvation and then remained constant. In healthy seabream juveniles, plasma glucose, protein, cholesterol, calcium and inorganic phosphorus are responsive to starvation and may be useful indicators of the nutritional status of the animals. Indicative baseline reference values for gilthead seabream juveniles starved for 24 h and held at optimum temperature are: protein, 3.7–4.9 g dl−1; cholesterol, 341–407 mg dl−1; calcium, 13.1–8.0 mg dl−1; and inorganic phosphorus, 10–14.2 mg dl−1. Plasma triglycerides, along with plasma enzyme activities, may be useful as indicators of short term starvation. For these parameters baseline values after 1 week of starvation were: triglycerides: 138–230 mg dl−1; ALP: 58–125 U L−1; AST: 15–127 U L−1; and LDH 61–677 U L−1. Plasma glucose is only responsive to longer starvation periods, remaining relatively stable during the first week of starvation, and ranging from 59 to 196 mg dl−1.

A trial was undertaken to estimate the protein requirement of sharpsnout sea bream ( Diplodus puntazzo ) and the protein sparing of dietary lipids. Ten diets were formulated to contain 5 protein levels (ranging from 15 to 55%) and two lipid levels (12 and 18%). Each diet was assigned to duplicate groups of 15 fish with a mean individual body weight of 49.3 g. A quadratic model was used to adjust weight gain and N retention (g kg ABW − 1 day − 1 ) to dietary protein levels. Based on that model, optimum dietary protein requirement was estimated to be 42.9% for maximum weight gain and 43.8% for maximum N retention, corresponding to a protein intake of 7.68 g kg ABW − 1 day − 1 . Protein requirement for maintenance was estimated to be 0.71 g kg ABW − 1 day − 1 . Dietary lipid level improved protein utilization efficiency but did not affect protein requirement. Whole-body protein content increased with dietary lipids and protein content, but no other relevant differences in body composition were noticed. Hepatosomatic index increased with dietary starch and lipid levels and was directly correlated to liver glycogen content. Diet composition affected plasma glucose clearance and cholesterolaemia but not plasma protein and triglyceride levels.

The present work aims to study the effect of a soluble non-starch polysaccharide (NSP), guar gum on white sea bream intestinal health through oxidative status and distal intestine morphology evaluation. A control diet was formulated to contain 40% crude protein, 14% crude lipids and 35% pregelatinized maize starch. Three other diets were formulated to include the same levels of all ingredients as control diet except for guar gum, which was included at 4% (diet GG4), 8% (diet GG8) or 12% (diet GG12). Compared to the control, lower catalase (CAT), superoxide dismutase (SOD) and glutathione reductase (GR) activities and higher SOD, glutathione peroxidase (GPX) and glucose-6-phosphate dehydrogenase (G6PD) activities were observed in the whole intestine of fish fed with diets GG4 and GG12, respectively. Thiobarbituric acid-reacting substances (TBARS) levels were unaffected by diet composition. No morphological alterations in the distal intestine were found among groups. Overall, data on key enzymes of the antioxidant enzymatic defense mechanism suggested that diet-induced reactive oxygen species (ROS) generation is dependent on guar gum inclusion levels and low dietary inclusion of soluble NSP (up to 4%) may have a gut oxidation stress prevention effect.

The effect of dietary protein reduction balanced by an increase in carbohydrate (starch) level on growth performance, feed utilization and intermediary metabolism of Senegalese sole juveniles was evaluated at two temperatures, 12 and 18°C. For that purpose two isolipidic (16% lipids) diets were formulated to contain 550gkg−1 protein and 90gkg−1 starch (diet HP:LC), and 450gkg−1 protein and 200gkg−1 starch (diet LP:HC). Each experimental diet was fed to triplicate groups of 20 fish (initial body weight: 15.9g) within each temperature. Diets had no effect on growth and feed utilization. Temperature affected growth but not feed efficiency, with fish growing more at 18°C. Fatty acid synthetase and glutamate dehydrogenase activities were higher at 12°C than at 18°C while activity of the other measured enzymes was not affected by water temperature. Glucokinase and malic enzyme activities were lower while fructose 1,6-bisphosphatase activity was higher in fish fed the HP:LC diet. Our data suggest that protein can be reduced from 550 gkg−1 to 450 gkg−1 by increasing starch level in high lipid diets for Senegalese sole juveniles without affecting overall performance. A reduction in protein content through an increase in dietary starch decreases hepatic gluconeogenesis. Increasing temperature from 12°C to 18°C improves fish growth but does not affect feed efficiency.

Under intensive culture conditions, fish are subject to increased stress owing to environmental (water quality and hypoxia) and health conditions (parasites and infectious diseases). All these factors have negative impacts on fish well-being and overall performance, with consequent economic losses. Though good management practices contribute to reduce stressor effects, stress susceptibility is always high under crowded conditions. Adequate nutrition is essential to avoid deficiency signs, maintain adequate animal performance and sustain normal health. Further, it is becoming evident that diets overfortified with specific nutrients [amino acids, essential fatty acids (FAs), vitamins or minerals] at levels above requirement may improve health condition and disease resistance. Diet supplements are also being evaluated for their antioxidant potential, as fish are potentially at risk of peroxidative attack because of the large quantities of highly unsaturated FAs in both fish tissues and diets. Functional constituents other than essential nutrients (such as probiotics, prebiotics and immunostimulants) are also currently being considered in fish nutrition aiming to improve fish growth and/or feed efficiency, health status, stress tolerance and resistance to diseases. Such products are becoming more and more important for reducing antibiotic utilization in aquafarms, as these have environmental impacts, may accumulate in animal tissues and increase bacterial resistance. This study reviews knowledge of the effect of diet nutrients on health, welfare and improvement of disease resistance in fish.

The effect of dietary carbohydrate complexity on growth, feed utilization, and glycemia was studied in European sea bass juveniles. Four isonitrogenous (50% crude protein) and isolipidic (15% crude lipids) diets were formulated to contain 20% pregelatinized maize starch (PGS diet), dextrin (DEX diet), maltose (MAL diet), or glucose (GLU diet). No effect of dietary carbohydrate complexity on growth was noticed. Feed efficiency and protein efficiency ratio were lower in fish fed the GLU diet than in the other groups, whereas the opposite was observed for feed intake. Plasma glucose peaked 3–4 h after feeding in fish fed the MAL and GLU diets, whereas in fish fed the PGS and DEX diets the peak was reached 5–6 h after feeding. Peak plasma glucose concentration (13 mmol/L) was higher in fish fed the GLU diet than the other diets (9 mmol/L). Shorter hyperglycemia duration was observed in fish fed the MALT and GLU diets (6 h) than the PGS and DEX diets (10 h). Complex carbohydrates delayed plasma glucose concentration peak compared with simple sugars, whereas the opposite was observed for hyperglycemia duration. Overall, dietary maltose, dextrin, and starch were apparently better utilized as energy source than glucose by European sea bass juveniles.

A glucose tolerance test was performed in white sea bream Diplodus sargus, juveniles to evaluate the effect of a glucose load on plasma glucose, insulin, triacylglyceride levels, and on liver glycogen storage in order to study the capability of glucose utilization by this species. After being fasted for 48 h, fish were intraperitoneally injected with either 1 g of glucose per kg body weight or a saline solution. Plasma glucose rose from a basal level of 4 to a peak of 18-19 mmol l(-1), 2-4 h after glucose injection and fish exhibited hyperglycemia for 9 h. An insulin peak (from 0.5 to 0.8 ng ml(-1)) was observed 2-6 h after glucose injection, and basal value was attained within 9 h. Liver glycogen peaked 6-12 h after the glucose load and thereafter decreased to the basal value which was attained 24 h after injection. Plasma triacylglycerides in glucose-injected fish were only significantly higher than the basal value 12 h after injection. Glucose-injected fish generally showed lower plasma triacylglyceride levels than control fish. Our results indicate that under these experimental conditions, glucose acts as an insulin secretagogue in white sea bream juveniles. Moreover, insulin may have contributed to restoring basal plasma glucose levels by enhancing glucose uptake in the liver. Further studies are needed to corroborate the lipolytic action of glucose. Clearance of glucose from the blood stream was fast, comparatively to other species, indicating that white sea bream has a good capability of glucose utilization.

This study assessed the effect of short (one or two weeks) feed deprivation periods on compensatory growth response of gilthead seabream juveniles. A 10 weeks growth trial was performed and three different feeding protocols were tested: control group (C) fed to apparent satiation twice a day, 6 days a week, during the whole experimental period; one week or two weeks unfed groups (groups U1 and U2, respectively) and re-fed for the rest 8 weeks of the trial as the control group. Each feeding protocol was tested in triplicate groups of fish with an initial body weight of 58 g. Starvation for one or two weeks induced significant losses of body weight that, comparatively to the control group, totaled 18.5 and 30.5% for U1 and U2 group, respectively. An intense mobilization of liver lipid and glycogen was observed after 1 or 2 weeks of starvation while perivisceral lipids, eviscerated-body lipids and energy contents were only decreased in fish unfed for 2 weeks. During the subsequent re-feeding period no recovery of body weight lost was noticed in the previously unfed groups, and feed intake and feed efficiency were identical in all groups. No differences between slopes of growth trajectory between the control and unfed groups were noticed, indicating no convergence of growth of unfed groups towards that of control group. A total recovery of the whole-body composition, organ indices, liver and viscera composition was observed at the end of the trial. Overall, gilthead seabream juveniles were not able to compensate growth after the feed starvation imposed. Therefore, it can be concluded, that under the experimental conditions applied short – one or two weeks – feed restriction periods are not advisable as management strategy to be used in gilthead seabream production.

A 74-day trial was undertaken to evaluate the effects of temperature (16 and 22 °C) and dietary protein/lipid ratio on the performance of juvenile Senegalese sole (mean body weight: 6.4 g). Four experimental diets were formulated to contain two protein levels (550 g kg−1 and 450 g kg−1) combined with two lipid levels (80 g kg−1 and 160 g kg−1). Growth was higher at 22 °C and within each temperature in fish fed diets 55P8L and 45P16L. Feed efficiency, N retention (% NI) and energy retention (% EI) were higher at 22 and at both temperatures in fish fed diet 55P8L. Temperature affected whole-body composition, with dry matter, protein, lipid and energy being higher and ash lower in fish kept at higher temperature. Independently of temperature, whole-body lipid, energy and ash were higher and protein was lower in fish fed the high-lipid diets. Visceral and hepatosomatic indices were not affected by diet composition but were higher in fish kept at 16 °C. Liver glycogen and lipid contents and activities of glutamate dehydrogenase, alanine and aspartate aminotransferases were not affected by diet or water temperature. Malic enzyme (ME) and glucose 6-phosphate dehydrogenase activities were higher in fish fed the low-lipid diets. ME activity was higher at lower temperature. In conclusion, increasing water temperature from 16 to 22 °C improves growth and feed efficiency of Senegalese sole juveniles; regardless of water temperature, the diet with 550 g kg−1 protein and 80 g kg−1 lipid promoted the best growth and feed efficiency.

A study was carried out with gilthead sea bream juveniles to assess the effect of water temperature (18 and 25°C) and dietary pregelatinized starch level (10, 20 and 30%) on digestibility of protein and starch and on the activity of proteolytic and amylolytic enzymes. ADC of pregelatinized starch was very high (>99%) irrespectively of dietary inclusion level, and it was not affected by water temperature. ADC of protein was also high (>90%) but improved at the higher water temperature. Dietary starch interacted with protein digestibility, which decreased as dietary starch level increased. Temperature affected both acid and basic protease activities, with acid protease activity being higher at 25°C and basic protease activity being higher at 18°C. However, total proteolytic activity and amylase activities were not affected by water temperature. Dietary carbohydrate exerted no effect on proteolytic or amylolitic activities. It is concluded that gilthead sea bream juveniles digest pregelatinized starch very efficiently irrespective of water temperature, due to adjustments of amylase activity to cope with temperature differences. Pregelatinized starch interacts negatively with protein digestibility, with the ADC of protein decreasing as dietary starch levels increase.