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© 2021 by the authors., On-growing juveniles of gilthead sea bream were acclimated for 45 days to mild-hypoxia (M-HYP, 40–60% O2 saturation), whereas normoxic fish (85–90% O2 saturation) constituted two different groups, depending on if they were fed to visual satiety (control fish) or pair-fed to M-HYP fish. Following the hypoxia conditioning period, all fish were maintained in normoxia and continued to be fed until visual satiation for 3 weeks. The time course of hypoxia-induced changes was assessed by changes in blood metabolic landmarks and muscle transcriptomics before and after exhaustive exercise in a swim tunnel respirometer. In M-HYP fish, our results highlighted a higher contribution of aerobic metabolism to whole energy supply, shifting towards a higher anaerobic fitness following normoxia restoration. Despite these changes in substrate preference, M-HYP fish shared a persistent improvement in swimming performance with a higher critical speed at exercise exhaustion. The machinery of muscle contraction and protein synthesis and breakdown was also largely altered by mild-hypoxia conditioning, contributing this metabolic re-adjustment to the positive regulation of locomotion and to the catch-up growth response during the normoxia recovery period. Altogether, these results reinforce the presence of large phenotypic plasticity in gilthead sea bream, and highlights mild-hypoxia as a promising prophylactic measure to prepare these fish for predictable stressful events., This work was financially supported by a grant from the European Commission of the European Union under the Horizon 2020 research infrastructure project AQUAEXCEL2020 (652831) to J.P-S. Additional funding was obtained by a Spanish MICINN project (Bream-AquaINTECH, RTI2018–094128-B-I00). J.A.M.-S. received a Postdoctoral Research Fellowship (Juan de la CiervaFormación, Reference FJCI-2014-20,161).

© 2021 by the authors., The physiological and endocrine benefits of sustained exercise in fish were largely demonstrated, and this work examines how the swimming activity can modify the effects of two diets (high-protein, HP: 54% proteins, 15% lipids; high-energy, HE: 50% proteins, 20% lipids) on different growth performance markers in gilthead sea bream juveniles. After 6 weeks of experimentation, fish under voluntary swimming and fed with HP showed significantly higher circulating growth hormone (GH) levels and plasma GH/insulin-like growth-1 (IGF-1) ratio than fish fed with HE, but under exercise, differences disappeared. The transcriptional profile of the GH-IGFs axis molecules and myogenic regulatory factors in liver and muscle was barely affected by diet and swimming conditions. Under voluntary swimming, fish fed with HE showed significantly increased mRNA levels of capn1, capn2, capn3, capns1a, n3, and ub, decreased gene and protein expression of Ctsl and Mafbx and lower muscle texture than fish fed with HP. When fish were exposed to sustained exercise, diet-induced differences in proteases’ expression and muscle texture almost disappeared. Overall, these results suggest that exercise might be a useful tool to minimize nutrient imbalances and that proteolytic genes could be good markers of the culture conditions and dietary treatments in fish., This study was supported by the projects from the “Ministerio de Economía y Competitividad” (MINECO) AGL2015-70679-R and RTI2018-100757-B-I00 to J.G. and J.B., and the “Xarxa de Refèrencia d’R+D+I en Aqüicultura” and the 2017SGR1574 from the “Generalitat de Catalunya”. M.P.- A., I.G.-P. and E.J.V. were supported by predoctoral fellowships from the MINECO, BES-2016-078697, PRE2019-089578 and BES-2013-062949, respectively.

Diisononyl phthalate (DiNP) is a plasticizer used to improve plastic performance in a large variety of items which has been reported as an endocrine-disrupting chemical (EDC) in several organisms. The endocannabinoid system (ECS) is a cellular signaling system, whose functionality is tightly involved with reproductive function. The aim of the present study was the assessment of the effects of DiNP on the gonadal ECS and on the reproductive function of male gilthead sea bream Sparus aurata, an important marine aquacultured species in Europe, during the reproductive season. Fish were fed for 21 days with two diets contaminated with different nominal concentrations of DiNP (DiNP LOW at 15 µg DiNP kg−1 bw day−1 and DiNP HIGH at 1500 µg DiNP kg−1 bw day−1), based on the tolerable daily intake (TDI) ruled by the European Food Safety Authority for humans. The transcription of several genes related to the ECS was affected by the DiNP. Specifically, DiNP reduced the levels of endocannabinoids and endocannabinoid-like mediators, concomitant with the increase of fatty acid amide hydrolase (FAAH) activity. At the histological level, DiNP LOW induced the highest occurrence of individuals with regressed testes. Steroidogenesis was affected significantly, since plasma 11-ketotestosterone (11-KT), the main active androgen in fish, was significantly decreased by the DiNP HIGH treatment, while plasma 17β-estradiol (E2) levels were raised, associated with an increase of the gonadosomatic index (GSI). Additionally, the level of testosterone (T) was significantly increased in the DiNP LOW group, however, the same DiNP concentration reduced the levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P). The production of sperm was in general not affected, since spermiation index, sperm density, survival and the duration of forward motility did not exhibit any changes compared to controls. However, computer-assisted sperm analysis (CASA) showed that DiNP reduced the percentage of motile cells. The results clearly suggest a negative effect of DiNP via the diet on the male endocrine system of gilthead sea bream during the reproductive season., This work has received funding from Progetti di Rilevante Interesse Nazionale (PRIN) 2010–2011 (prot 2010W87LBJ) to OC and from the European Union’s Horizon 2020 research and innovation program under the TNA programme (Project ID AE030014) within AQUAEXCEL2020 project (652831) to IFP and OC for accessing to IATS-CSIC facilities.

Amoebic gill disease (AGD) is one of the main diseases affecting Atlantic salmon (Salmo salar L.) mariculture. Hallmarks of AGD are hyperplasia of the lamellar epithelium and increased production of gill mucus. This study investigated the expression of genes involved in mucus secretion, cell cycle regulation, immunity and oxidative stress in gills using a targeted 21-gene PCR array. Gill samples were obtained from experimental and natural Neoparamoeba perurans infections, and sampling points included progressive infection stages and post-freshwater treatment. Up-regulation of genes related to mucin secretion and cell proliferation, and down-regulation of pro-inflammatory and pro-apoptotic genes were associated with AGD severity, while partial restoration of the gill homeostasis was detected post-treatment. Mucins and Th2 cytokines accoun ted for most of the variability observed between groups highlighting their key role in AGD. Two mucins (muc5, muc18) showed differential regulation upon disease. Substantial up-regulation of the secreted muc5 was detected in clinical AGD, and the membrane bound muc18 showed an opposite pattern. Th2 cytokines, il4/13a and il4/13b2, were significantly upregulated from 2 days post-infection onwards, and changes were lesion-specific. Despite the differences between experimental and natural infections, both yielded comparable results that underline the importance of the studied genes in the respiratory organs of fish, and during AGD progression., Irish Research Council (Employment Based Postgraduate Programme Project ID EBPPG/2013/2), European Commission under the TNA programme (project ID AE030036) within AQUAEXCEL2020 project (652831)., CSIC PIE project no. 201740E013.

The potential benefits of a commercial preparation of heptanoate (NOREL, HEPTON®) were evaluated in an 11‐week gilthead sea bream feeding trial (May–August), using a factorial design with four isoproteic and isoenergetic diets. Fish meal (FM) was added at 200 g/kg in D1–D2 diets and at 50 g/kg in D3–D4 diets, which also contained fish peptones and plant proteins as source of proteins. Heptanoate was added at 3 g/kg in D2 and D4 diets. All fish grew from 13–14 g to 81–84 g with an overall feed efficiency (FE) of 0.91–0.94. An early impairment of FE (weeks 1–4) was found with the standard FM‐based diet (D1), but this detrimental condition was reversed by heptanoate, increasing FE from 0.88 in D1 fish to 0.99 in D2 fish. Further improvements were progressively diluted over time, remaining D2 and D3–D4 fed fish almost undistinguishable through all the trial. Heptanoate supplementation produced higher hepatic glycogen depots, but no signs of histopathological damage were found in liver or intestine. Other lasting heptanoate effects included changes in plasma antioxidant capacity, plasma cortisol and growth hormone levels, and measures of respirometry in swimming performance tests. Altogether, it supports the potential use of heptanoate to speed up adaptive and healthy metabolic states of farmed fish to cope with challenging culture conditions., This work has been carried out with the financial support from NOREL S.A. and BioMar. Additional funding has been received by Spanish MINECO project no. AGL2013‐48560‐R and Generalitat Valenciana (PROMETEO‐FASE II/2014/085). MCP was supported by MINECO through grant FPDI‐2013‐15741 and by CSIC PIE project no. 201740E013. JAMS was supported by a postdoctoral research fellowship (Juan de la Cierva‐Formación, Reference FJCI‐2014‐20161) from MINECO

Juveniles of the protandrous hermaphrodite gilthead sea bream (Sparus aurata) were fed from early life stages to completion of sex maturation with plant-based diets formulated by BioMar. Total fish meal (FM) was included at 25% in the control diet (D1) and at 5% in the other three diets (D2, D3, D4). Added oil was either fish oil (FO) (D1) or a blend of vegetable oils replacing 58% (D2) and 84% (D3, D4) of FO. A commercial butyrate preparation (BP-70® NOREL) was added to the D4 diet at 0.4%. All fish grew fast through a three-year ongrowing cycle with overall specific growth rates of 1.4%, 0.7% and 0.5% for fish harvest at 300 g, 1 kg and 1.5–1.7 kg, respectively. Overall feed efficiency decreased progressively as fish size increased from 0.99 in 300 g fish to 0.8–0.7 in 1–1.7 kg fish. At the last stage, a clear sexual dimorphism was found for body weight and hepatosomatic index when all sampled fish were considered as a whole. A sexual dimorphism was also found for sex steroids with a peak of estradiol in the females sampled in October–December, whereas the peak of 11-ketotestosterone was delayed in males to December. Plasma levels of testosterone were similar in both sexes. The two first components of principal component analysis (PCA) explained >90% of total variance of plasma levels of sex steroids. The displacement along X-axis clearly separated males and females, whereas the movement along Y-axis was related to sampling time. An androgenic effect in the steroid plasma profile of fish fed plant-based diets was also shown, which was especially evident for the low FM/FO diet formulation (D3). This effect was reversed by butyrate and the female/male ratio of D4 fish (age class +3) did not differ from that of control fish, whereas the proportion of females in D2 + D3 fish was higher (P, This work has been carried out with financial support from the European Union (ARRAINA, FP7-KBBE-2011-5-288925, Advanced Research Initiatives for Nutrition and Aquaculture). Additional funding was obtained from the Spanish MINECO (MI2-Fish, AGL2013-48560; Pubertrait, AGL2016-75400) and from Generalitat Valenciana (PROMETEO FASE II-2014/085 and 051).

The growth hormone (GH)/insulin-like growth factors (IGFs) endocrine axis is the main growth-regulator system in vertebrates. Some authors have demonstrated the positive effects on growth of a sustained-release formulation of a recombinant bovine GH (rBGH) in different fish species. The aim of this work was to characterize the effects of a single injection of rBGH in fingerlings of gilthead sea bream on growth, GH-IGF axis, and both myogenic and osteogenic processes. Thus, body weight and specific growth rate were significantly increased in rBGH-treated fish respect to control fish at 6 weeks post-injection, whereas the hepatosomatic index was decreased and the condition factor and mesenteric fat index were unchanged, altogether indicating enhanced somatic growth. Moreover, rBGH injection increased the plasma IGF-I levels in parallel with a rise of hepatic mRNA from total IGF-I, IGF-Ic and IGF-II, the binding proteins IGFBP-1a and IGFBP-2b, and also the receptors IGF-IRb, GHR-I and GHR-II. In skeletal muscle, the expression of IGF-Ib and GHR-I was significantly increased but that of IGF-IRb was reduced; the mRNA levels of myogenic regulatory factors, proliferation and differentiation markers (PCNA and MHC, respectively), or that of different molecules of the signaling pathway (TOR/AKT) were unaltered. Besides, the growth inhibitor myostatin (MSTN1 and MSTN2) and the hypertrophic marker (MLC2B) expression resulted significantly enhanced, suggesting altogether that the muscle is in a non-proliferative stage of development. Contrarily in bone, although the expression of most molecules of the GH/IGF axis was decreased, the mRNA levels of several osteogenic genes were increased. The histology analysis showed a GH induced lipolytic effect with a clear decrease in the subcutaneous fat layer. Overall, these results reveal that a better growth potential can be achieved on this species and supports the possibility to improve growth and quality through the optimization of its culture conditions., E.J.V. and E.L. are supported by a predoctoral fellowship from the “Ministerio de Ciencia e Innovación” (MICINN), and A.M. by the University of Barcelona (APIF-2012). This study was supported by the project AGL2012-39768 (MICINN) to J.G., and the “Xarxa de Refèrencia d’R+D+I en Aqüicultura” and the 2014SGR-01371 from the “Generalitat de Catalunya”.

An olive oil bioactive extract (OBE) rich in bioactive compounds like polyphenols, triterpenic acids, long-chain fatty alcohols, unsaturated hydrocarbons, tocopherols and sterols was tested (0, 0·08, 0·17, 0·42 and 0·73 % OBE) in diets fed to sea bream (Sparus aurata) (initial weight: 5·4 (sd1·2) g) during a 90-d trial (four replicates). Fish fed diets containing 0·17 and 0·42 % OBE were 5 % heavier (61·1 (sd1·6) and 60·3 (sd1·1) g, respectively) than those of the control group (57·0 (sd0·7) g), although feed conversion ratio and specific feed intake did not vary. There were no differences in lipid peroxidation (LPO) levels, catalase, glutathione reductase and glutathioneS-transferase activities in the intestine and liver, although there was a tendency of lower intestinal and hepatic LPO levels in fish fed OBE diets. No differences in villus size were found among treatments, whereas goblet cell density in the control group was on average14·3 % lower than in fish fed OBE diets. The transcriptomic profiling of intestinal markers, covering different biological functions like (i) cell differentiation and proliferation, (ii) intestinal permeability, (iii) enterocyte mass and epithelial damage, (iv) IL and cytokines, (v) pathogen recognition receptors and (vi) mitochondria function, indicated that among the eighty-eight evaluated genes, twenty-nine were differentially expressed (0·17 % OBE diet), suggesting that the additive has the potential of improving the condition and defensive role of the intestine by enhancing the maturation of enterocytes, reducing oxidative stress, improving the integrity of the intestinal epithelium and enhancing the intestinal innate immune function, as gene expression data indicated.

European aquaculture is an industry with a high sustainability profile contributing to the supply of safe seafood. However, several diseases can affect farmed fish and it is imperative to find alternatives for chemotherapeutic treatments when disease outbreaks occur. Maintenance of health through nutrition is well-establish in modern animal farming, and amino acids (AA) are promising candidates as functional additives to improve fish health. Therefore, the goal of this research is to provide a better understanding of the influence of tryptophan supplementation on nutritional condition and immune mechanisms in fish. Triplicate groups of fish (13.3 ± 0.3g) previously fed with a fishmeal-based diet were either fed a control diet with an extreme formulation (0% fishmeal) but meeting the AA requirements (CTRL), or the SUP diet, formulated as the CTRL with an increase in tryptophan (TRP) content. After 2 and 13 weeks of feeding, head-kidney (HK), liver (L) and white skeletal muscle (WSM) were collected for gene expression, whereas plasma was suited for humoral immune parameters. A holistic approach using transcriptomic, humoral and zootechnical parameters was undertaken. The expression of 29–31 genes for WSM, L or HK confirms an effect due to the treatment across time. A two-way ANOVA analysis revealed that 15–24 genes varied significantly depending on the tissue, and the multivariate analysis by means of PLS-DA explained (R) and predicted (Q) with four components up to 93% and 78% of total variance, respectively. Component 1 (R = 50.06%) represented the time effects, whereas components 2 (24.36%) and 3 (13.89%) grouped fish on the basis of dietary treatment, at early sampling. The HK results in particular suggest that fish fed SUP diet displayed an immunostimulated state at 2 weeks. No major differences were observed in plasma humoral parameters, despite an increase in antiprotease and peroxidase activities after 13 weeks regardless of dietary treatment. These results suggest that tryptophan supplementation may improve the seabream immune status after 2 weeks. Hence, the use of functional feeds is especially relevant during a short-term feeding period before a predictable stressful event or disease outbreak, considering that these putative advantageous effects seem to disappear after a 13 weeks feeding period., This work was partially supported by Projects ALISSA (reference ALG-01-0247-FEDER-3520), UID/Multi/04423/2019, IF/00197/2015 and IF/00482/2014, financed by Portugal and the European Union through FEDER, COMPETE 2020 and CRESC Algarve 2020, in the framework of Portugal 2020, and through the COMPETE and Operational Human Potential Programmes and national funds through Fundação para a Ciência e a Tecnologia (FCT, P ortugal). L. Ramos-Pinto, S. Engrola and B. Costas were supported by FCT, Portugal (PD/BDE/114436/2016, IF/00482/2014 and IF/00197/2015, respectively).

Two different O2 levels (normoxia: 75¿85% O2 saturation; moderate hypoxia: 42¿43% O2 saturation) and stocking densities (LD: 9.5, and HD: 19 kg/m3) were assessed on gilthead sea bream (Sparus aurata) in a 3-week feeding trial. Reduced O2 availability had a negative impact on feed intake and growth rates, which was exacerbated by HD despite of the improvement in feed efficiency. Blood physiological hallmarks disclosed the enhancement in O2-carrying capacity in fish maintained under moderate hypoxia. This feature was related to a hypo-metabolic state to cope with a chronic and widespread environmental O2 reduction, which was accompanied by a differential regulation of circulating cortisol and growth hormone levels. Customized PCR-arrays were used for the simultaneous gene expression profiling of 34¿44 selected stress and metabolic markers in liver, white skeletal muscle, heart, and blood cells. The number of differentially expressed genes ranged between 22 and 19 in liver, heart, and white skeletal muscle to 5 in total blood cells. Partial Least-Squares Discriminant Analysis (PLS-DA) explained [R2Y(cum)] and predicted [Q2Y(cum)] up to 95 and 65% of total variance, respectively. The first component (R2Y = 0.2889) gathered fish on the basis of O2 availability, and liver and cardiac genes on the category of energy sensing and oxidative metabolism (cs, hif-1¿, pgc1¿, pgc1ß, sirts 1-2-4-5-6-7), antioxidant defense and tissue repair (prdx5, sod2, mortalin, gpx4, gr, grp-170, and prdx3) and oxidative phosphorylation (nd2, nd5, and coxi) highly contributed to this separation. The second component (R2Y = 0.2927) differentiated normoxic fish at different stocking densities, and the white muscle clearly promoted this separation by a high over-representation of genes related to GH/IGF system (ghr-i, igfbp6b, igfbp5b, insr, igfbp3, and igf-i). The third component (R2Y = 0.2542) discriminated the effect of stocking density in fish exposed to moderate hypoxia by means of hepatic fatty acid desaturases (fads2, scd1a, and scd1b) and muscle markers of fatty acid oxidation (cpt1a). All these findings disclose the different contribution of analyzed tissues (liver ¿ heart > muscle > blood) and specific genes to the hypoxic- and crowding stress-mediated responses. This study will contribute to better explain and understand the different stress resilience of farmed fish across individuals and species., This work has been carried out with financial support from the European Commission of the European Union, under the Horizon 2020 research infrastructure project AQUAEXCEL2020 (652831) to JP-S. This publication reflects the views only of the authors, and the European Commission cannot be held responsible for any use which may be made of the information contained therein. JM-S was funded by a Postdoctoral Research Fellowship (Juan de la Cierva-Formación, Reference FJCI-2014- 20161) and belongs to the Fish Welfare and Stress Network (AGL2016-81808-REDT) from the MINECO

Intensive aquaculture practices involve rearing fish at high densities. In these conditions, fish may be exposed to suboptimal dissolved O levels with an increased formation of reactive O species (ROS) in tissues. Seaweeds (SW) contain biologically active substances with efficient antioxidant capacities. This study evaluated the effects of dietary supplementation of heat-treated SW (5% Gracilaria vermiculophylla or 5% Ulva lactuca) on stress bioindicators in sea bream subjected to a hypoxic challenge. 168 fish (104.5 g average weight) were distributed in 24 tanks, in which eight tanks were fed one of three experimental diets for 34 days: (i) a control diet without SW supplementation, (ii) a control diet supplemented with Ulva, or (iii) a control diet with Gracilaria. Thereafter, fish from 12 tanks (n=4 tanks/dietary treatment) were subjected to 24 h hypoxia (1.3 mg O l) and subsequent recovery normoxia (8.6 mg O l). Hypoxic fish showed an increase in hematocrit values regardless of dietary treatment. Dietary modulation of the O-carrying capacity was conspicuous during recovery, as fish fed SW supplemented diets displayed significantly higher haemoglobin concentration than fish fed the control diet. After the challenge, survival rates in both groups of fish fed SW were higher, which was consistent with a decrease in hepatic lipid peroxidation in these groups. Furthermore, the hepatic antioxidant enzyme activities were modulated differently by changes in environmental O condition, particularly in sea bream fed the Gracilaria diet. After being subjected to hypoxia, the gene expression of antioxidant enzymes and molecular chaperones in liver and heart were down regulated in sea bream fed SW diets. This study suggests that the antioxidant properties of heat-treated SW may have a protective role against oxidative stress. The nature of these compounds and possible mechanisms implied are currently being investigated., This work has been carried out with financial support from the European Commission of the European Union, specific RTD Seventh Framework Programme under grant projects SEABIOPLAS (606032), AQUAEXCEL (262336) under TNA project 0132/09/04/14b (ALGAE-SPARUS). L.J.M. is supported by a Fundação para a Ciência e a Tecnologia (FCT) research position with exploratory grant IF/01314/2014/CP1231/CT0001 from Portugal. J.A.M.-S. is supported by a Postdoctoral Research Fellowship (Juan de la Cierva-Formación, reference FJCI-2014-20161) from the Spanish Ministry of Economy and Competitiveness.

The enhancement of the endocrine growth hormone (GH)/insulin-like growth factor I (IGF-I) system by the treatment with a sustained release formulation of a recombinant bovine GH (rBGH), is a good strategy to investigate growth optimization in aquaculture fish species. To further deepen into the knowledge of rBGH effects in fish and to estimate the growth potential of juveniles of gilthead sea bream, the present work evaluated rBGH injection on growth, GH/IGF-I axis and lipid metabolism modulation, and explored the conservation of GH effects provoked by the in vivo treatment using in vitro models of different tissues. The rBGH treatment increased body weight and specific growth rate (SGR) in juveniles and potentiated hyperplastic muscle growth while reducing circulating triglyceride levels. Moreover, the results demonstrated that the in vivo treatment enhanced also lipolysis in both isolated hepatocytes and adipocytes, as well as in day 4 cultured myocytes. Furthermore, these cultured myocytes extracted from rBGH-injected fish presented higher gene expression of GH/IGF-I axis-related molecules and myogenic regulatory factors, as well as stimulated myogenesis (i.e. increased protein expression of a proliferation and a differentiation marker) compared to Control fish-derived cells. These data, suggested that cells in vitro can retain some of the pathways activated by in vivo treatments in fish, what can be considered an interesting line of applied research. Overall, the results showed that rBGH stimulates somatic growth, including specifically muscle hyperplasia, as well as lipolytic activity in gilthead sea bream juveniles., E.J.V., E.L. and M.P.-A. were supported by predoctoral fellowships from the “Ministerio de Economía y Competitividad” (MINECO). This study was supported by the projects from the MINECO AGL2012-39768 and AGL2015-70679-R to J.G., and AGL2014-57974-R to I.N. and E.C., and the “Xarxa de Refèrencia d'R+D+I en Aqüicultura” and the 2014SGR-01371 from the “Generalitat de Catalunya”.

European seabass (Dicentrarchus labrax) production is often hampered by bacterial infections such as photobacteriosis caused by Photobacterium damselae subsp. piscicida (Phdp). Since diet can impact fish immunity, this work investigated the effect of dietary supplementation of 5% Gracilaria sp. aqueous extract (GRA) on seabass antioxidant capacity and resistance against Phdp. After infection, mortality was delayed in fish fed GRA, which also revealed increased lysozyme activity levels, as well as decreased lipid peroxidation, suggesting higher antioxidant capacity than in fish fed a control diet. Dietary GRA induced a down-regulation of hepatic stress-responsive heat shock proteins (grp-78, grp-170, grp-94, grp-75), while bacterial infection caused a down-regulation in antioxidant genes (prdx4 and mn-sod). Diet and infection interaction down-regulated the transcription levels of genes associated with oxidative stress response (prdx5 and gpx4) in liver. In head-kidney, GRA led to an up-regulation of genes associated with inflammation (il34, ccr9, cd33) and a down-regulation of genes related to cytokine signalling (mif, il1b, defb, a2m, myd88). Additionally, bacterial infection up-regulated immunoglobulins production (IgMs) and down-regulated the transcription of the antimicrobial peptide leap2 in head kidney. Overall, we found that GRA supplementation modulated seabass resistance to Phdp infection., This study is part of M.J. Peixoto PhD thesis. This work has received funding from the European Union’s Horizon 2020 research and innovation program under the TNA programme (project ID AE040085) within AQUAEXCEL2020 project (652831) to RF, LJM and ROAO for accessing to IATS-CSIC facilities.

Bisphenol A (BPA), a known endocrine disrupting chemical (EDC), was administered by diet to gilthead sea bream (Sparus aurata) in order to study its effects on the endocannabinoid system (ECS) and gonadal steroidogenesis. 2-year-old male gilthead sea bream were fed with two different concentrations of BPA (LOW at 4 and HIGH at 4000 &micro, g/kg body weight for 21 days during the reproductive season. Exposure to 4000 &micro, g BPA/kg bw/day (BPA HIGH) reduced sperm motility and altered the straight-line velocity (VSL) and linearity (LIN). Effects on steroidogenesis were evident, with testosterone (T) being up-regulated by both treatments and 11-ketotestosterone (11-KT) down-regulated by BPA HIGH. Plasma levels of 17&beta, estradiol (E2) were not affected. The Gonadosomatic Index (GSI) increased in the BPA HIGH group. Interestingly, the levels of endocannabinoids and endocannabinoid-like compounds were significantly reduced after both treatments. Unpredictably, a few changes were noticed in the expression of genes coding for ECS enzymes, while the receptors were up-regulated depending on the BPA dose. Reproductive markers in testis (leptin receptor (lepr), estrogen receptors (era, erb), progesterone receptors (pr) and the gonadotropin releasing hormone receptor (gnrhr)) were up-regulated. BPA induced the up-regulation of the hepatic genes involved in oogenesis (vitellogenin (vtg) and zona pellucida 1 (zp1)).

© The Author(s)., [Background]:In the animal production sector, enteritis is responsible for serious economic losses, and intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and animal production efficiency. The effect of enteric parasites on the gut function of teleost fish, which represent the most ancient bony vertebrates, is far from being understood. The intestinal myxozoan parasite Enteromyxum leei dwells between gut epithelial cells and causes severe enteritis in gilthead sea bream (Sparus aurata), anorexia, cachexia, growth impairment, reduced marketability and increased mortality., [Methods]: This study aimed to outline the gut failure in this fish-parasite model using a multifaceted approach and to find and validate non-lethal serum markers of gut barrier dysfunction. Intestinal integrity was studied in parasitized and non-parasitized fish by immunohistochemistry with specific markers for cellular adhesion (E-cadherin) and tight junctions (Tjp1 and Cldn3) and by functional studies of permeability (oral administration of FITC-dextran) and electrophysiology (Ussing chambers). Serum samples from parasitized and non-parasitized fish were analyzed using non-targeted metabolomics and some significantly altered metabolites were selected to be validated using commercial kits., [Results]: The immunodetection of Tjp1 and Cldn3 was significantly lower in the intestine of parasitized fish, while no strong differences were found in E-cadherin. Parasitized fish showed a significant increase in paracellular uptake measured by FITC-dextran detection in serum. Electrophysiology showed a decrease in transepithelial resistance in infected animals, which showed a diarrheic profile. Serum metabolomics revealed 3702 ions, from which the differential expression of 20 identified compounds significantly separated control from infected groups in multivariate analyses. Of these compounds, serum inosine (decreased) and creatine (increased) were identified as relevant and validated with commercial kits., [Conclusions]: The results demonstrate the disruption of tight junctions and the loss of gut barrier function, a metabolomic profile of absorption dysfunction and anorexia, which further outline the pathophysiological effects of E. leei., This work has been carried out with financial support from the European Union under grant projects ParaFishControl (H2020-634429) to ASB and Aquaexcel2020 (652831, TNA AE10004-INTEBREAM) to JF and JPS, and from the Spanish MINECO under AGL2013-48560-R project to ASB and JPS. APS was contracted under the ParaFishControl project, MCP under CSIC PIE project no. 201740E013 and IE under APOSTD/2016/037 grant by the “Generalitat Valenciana”. Centre for Marine Sciences (CCMAR) is supported by the Portuguese Foundation for Science and Technology (FCT) through project UID/Multi 04326/2019.

Ghrelin is involved in the regulation of growth in vertebrates through controlling different functions, such as feed intake, metabolism, intestinal activity or growth hormone (Gh) secretion. The aim of this work was to identify the sequences of preproghrelin and Ghrelin receptors (ghsrs), and to study their responses to different nutritional conditions in gilthead sea bream (Sparus aurata) juveniles. The structure and phylogeny of S. aurata preproghrelin was analyzed, and a tissue screening was performed. The effects of 21 days of fasting and 2, 5, 24 h, and 7 days of refeeding on plasma levels of Ghrelin, Gh and Igf-1, and the gene expression of preproghrelin, ghsrs and members of the Gh/Igf-1 system were determined in key tissues. preproghrelin and the receptors are well conserved, being expressed mainly in stomach, and in the pituitary and brain, respectively. Twenty-one days of fasting resulted in a decrease in growth while Ghrelin plasma levels were elevated to decrease at 5 h post-prandial when pituitary ghsrs expression was minimum. Gh in plasma increased during fasting and slowly felt upon refeeding, while plasma Igf-1 showed an inverse profile. Pituitary gh expression augmented during fasting reaching maximum levels at 1 day post-feeding while liver igf-1 expression and that of its splice variants decreased to lowest levels. Liver Gh receptors expression was down-regulated during fasting and recovered after refeeding. This study demonstrates the important role of Ghrelin during fasting, its acute down-regulation in the post-prandial stage and its interaction with pituitary Ghsrs and Gh/Igf-1 axis., The authors thank the personnel from the animal facilities at the School of Biology for the fish maintenance and to Piscimar for providing the fish. We also thank Prof. Jordi Garcia for his help on sequence analysis and primer design of Ghsrs. MP-A, EV, and NR-H are supported by predoctoral fellowships from the Ministerio de Economía y Competitividad (MINECO) BES-2016-078697, BES-2013-062949 and BES-2015-074654, respectively. This study was supported by the projects from the MINECO AGL2014-57974-R to IN and EC. and AGL2015-70679-R to JG, and the Xarxa de Referència d'R+D+I en Aqüicultura and the 2014SGR-01371 from the Generalitat de Catalunya.

The increasing manufacture of plastics and their mismanagement has turned plastic into a ubiquitous waste in the marine environment. Among all the substances conforming the plastic items, the effects of a dietary Bisphenol A (BPA) and Di-isononyl phthalate (DiNP) have been evaluated in adult male gilthead sea bream, focusing on their effects in the modulation of the Endocannabinoid System (ECS). In zebrafish, the ECS has been recently chosen as a new target for the activity of some Endocrine Disrupting Chemicals (EDC), since it represents a complex lipid signaling network essential for the well-being of the organisms. The results obtained in gilthead seabream showed that BPA and DiNP altered the structure and the biochemical composition of liver, increasing the presence of lipids and triglycerides and decreasing the glycogen and phospholipids. Moreover, the addition of BPA or DiNP in the gilthead sea bream diet altered the levels of endocannabinoids (EC) and EC-like mediators in the liver. These alterations were also associated to changes at the transcriptomic level of genes involved in lipid biosynthesis and ECS metabolism. At the central level, both BPA and DiNP reduced the expression of the endocannabinoid receptor type I (cnr1) and the neuropeptide Y (npy) as well as the levels of the endocannabinoid Anandamide (AEA), suggesting a downregulation of appetite. The results herein reported highlighted the negative effects of chronic dietary exposure to DiNP or BPA on ECS functions and lipid metabolism of male gilthead sea bream liver, showing a similar disruptive activity of these contaminants at metabolic level. Moreover, the novelty of the biomarkers used evidenced possible innovative endpoints for the development of novel OEDCS test guidelines., This work has received funding from Progetti di Rilevante Interesse Nazionale (PRIN) 2010 – 2011 (prot 2010W87LBJ) to OC and from the European Union's Horizon 2020 research and innovation program under the TNA program (project ID AE030014) within AQUAEXCEL2020 project (652831) to IFP and OC. This output reflects only the author's view and the European Union cannot be held responsible for any use that may be made of the information contained therein.

[Backgroud] Enteromyxum leei is a myxozoan parasite that produces a slow-progressing intestinal disease. This parasite invades the paracellular space of the intestinal epithelium and progresses from the posterior to the anterior intestine. The aim of the present study was to gain insights into fish T cell responses in the gilthead sea bream-E. leei infection model using a PCR-array with 30 signature molecules for different leukocyte responses in head kidney, spleen, anterior and posterior intestine., [Results] The PCR-array results suggest that E. leei induced migration of T cells from head kidney to intestines where TH1, CTL and TH17 profiles were activated and kept in balance by the upregulation of regulatory cytokines. These results were partially validated by the use of cross-reacting antibodies and BrdU immunostaining to monitor proliferation. Zap70 immunostaining supported the increased number of T cells in the anterior intestine detected by gene expression, but double staining with BrdU did not show active proliferation of this cell type at a local level, supporting the migration from lymphohaematopoietic tissues to the site of infection. Global analyses of the expression profiles revealed a clear separation between infected and exposed, but non-infected fish, more evident in the target organ. Exposed, non-infected animals showed an intermediate phenotype closer to the control fish., [Conclusions] These results evidence a clear modulation of the T cell response of gilthead sea bream upon E. leei infection. The effects occurred both at local and systemic levels, but the response was stronger and more specific at the site of infection, the intestine. Altogether, this research poses a promising basis to understand the response against this important parasite and establish effective preventive or palliative measures., This work has been carried out with financial support from the Spanish MINECO under project AGL2013-48560-R. Additional funding was provided by the European Union, through the Horizon H2020 research and innovation programme under grant agreement 634429 (ParaFishControl). This publication reflects only the authors’ view and the European Union cannot be held responsible for any use that may be made of the information contained herein. Further support was provided by Generalitat Valenciana (PROMETEOII/2014/085). MCP was contracted under CSIC PIE project no. 201740E013 and MINECO FPDI-2013-15741, and IE under APOSTD/2016/037 grant by the “Generalitat Valenciana”. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Sirtuins (SIRTs) represent a conserved protein family of deacetylases that act as master regulators of metabolism, but little is known about their roles in fish and livestock animals in general. The present study aimed to assess the value of SIRTs for the metabolic phenotyping of fish by assessing their co-expression with a wide-representation of markers of energy and lipid metabolism and intestinal function and health in two genetically different gilthead sea bream strains with differences in growth performance. Fish from the fast-growing strain exhibited higher feed intake, feed efficiency and plasma IGF-I levels, along with higher hepatosomatic index and lower mesenteric fat (lean phenotype). These observations suggest differences in tissue energy partitioning with an increased flux of fatty acids from adipose tissue toward the liver. The resulting increased risk of hepatic steatosis may be counteracted in the liver by reduced lipogenesis and enhanced triglyceride catabolism, in combination with a higher and more efficient oxidative metabolism in white skeletal muscle. These effects were supported by co-regulated changes in the expression profile of SIRTs (liver, sirt1; skeletal muscle, sirt2; adipose tissue, sirt5-6) and markers of oxidative metabolism (pgc1α, cpt1a, cs, nd2, cox1), mitochondrial respiration uncoupling (ucp3) and fatty acid and triglyceride metabolism (pparα, pparγ, elovl5, scd1a, lpl, atgl) that were specific to each strain and tissue. The anterior intestine of the fast-growing strain was better suited to cope with improved growth by increased expression of markers of nutrient absorption (fabp2), epithelial barrier integrity (cdh1, cdh17) and immunity (il1β, cd8b, lgals1, lgals8, sIgT, mIgT), which were correlated with low expression levels of sirt4 and markers of fatty acid oxidation (cpt1a). In the posterior intestine, the fast-growing strain showed a consistent up-regulation of sirt2, sirt3, sirt5 and sirt7 concurrently with increased expression levels of markers of cell proliferation (pcna), oxidative metabolism (nd2) and immunity (sIgT, mIgT). Together, these findings indicate that SIRTs may play different roles in the regulation of metabolism, inflammatory tone and growth in farmed fish, arising as powerful biomarkers for a reliable metabolic phenotyping of fish at the tissue-specific level., This work was funded by the Spanish MINECO (MI2-Fish, AGL2013-48560) and from Generalitat Valenciana (PROMETEO FASE II-2014/085). Additional funding was obtained from PerformFISH (Integrating Innovative Approaches for Competitive and Sustainable Performance across the Mediterranean Aquaculture Value Chain) EU Project (H2020-SFS-2016-2017; 727610)

[Background] Acclimation to abiotic challenges, including decreases in O2 availability, requires physiological and anatomical phenotyping to accommodate the organism to the environmental conditions. The retention of a nucleus and functional mitochondria in mature fish red blood cells makes blood a promising tissue to analyse the transcriptome and metabolic responses of hypoxia-challenged fish in an integrative and non-invasive manner., [Methods] Juvenile gilthead sea bream (Sparus aurata) were reared at 20–21 °C under normoxic conditions (> 85% O2 saturation) followed by exposure to a gradual decrease in water O2 concentration to 3.0 ppm (41–42% O2 saturation) for 24 h or 1.3 ppm (18–19% O2 saturation) for up to 4 h. Blood samples were collected at three different sampling points for haematological, biochemical and transcriptomic analysis., [Results] Blood physiological hallmarks remained almost unaltered at 3.0 ppm, but the haematocrit and circulating levels of haemoglobin, glucose and lactate were consistently increased when fish were maintained below the limiting oxygen saturation at 1.3 ppm. These findings were concurrent with an increase in total plasma antioxidant activity and plasma cortisol levels, whereas the opposite trend was observed for growth-promoting factors, such as insulin-like growth factor I. Additionally, gene expression profiling of whole blood cells revealed changes in upstream master regulators of mitochondria (pgcβ and nrf1), antioxidant enzymes (gpx1, gst3, and sod2), outer and inner membrane translocases (tom70, tom22, tim44, tim10, and tim9), components of the mitochondrial dynamics system (mfn2, miffb, miro1a, and miro2), apoptotic factors (aifm1), uncoupling proteins (ucp2) and oxidative enzymes of fatty acid β-oxidation (acca2, ech, and hadh), the tricarboxylic acid cycle (cs) and the oxidative phosphorylation pathway. The overall response is an extensive reduction in gene expression of almost all respiratory chain enzyme subunits of the five complexes, although mitochondrial-encoded catalytic subunits and nuclear-encoded regulatory subunits of Complex IV were primarily increased in hypoxic fish., [Conclusions] Our results demonstrate the re-adjustment of mitochondrial machinery at transcriptional level to cope with a decreased basal metabolic rate, consistent with a low risk of oxidative stress, diminished aerobic ATP production and higher O2-carrying capacity. Taken together, these results suggest that whole blood cells can be used as a highly informative target tissue of metabolic condition., This work was financially supported by a grant from the European Commission of the European Union under the Horizon 2020 research infrastructure project AQUAEXCEL2020 (652831). Additional funding was provided by Generalitat Valenciana (PROMETEOII/2014/085). JAMS received a Postdoctoral Research Fellowship (Juan de la Cierva-Formación, Reference FJCI-2014-20,161) from MINECO.

The seven sirtuin (SIRT) counterparts of higher vertebrates were identified and molecularly characterized in a farmed fish of the Sparidae family, order Perciformes. These proteins are NAD+-dependent deacetylases that couple protein deacetylation with the energy status of the cell via the cellular NAD+/NADH ratio with a strict conservation of the characteristic catalytic domain surrounded by divergent N- and C- terminal regions. Phylogenetic analysis showed three major clades corresponding to SIRT1–3, SIRT4–5, and SIRT6–7 that reflected the present hierarchy of vertebrates and the accepted classification of SIRTs. Transcriptional studies revealed a ubiquitous SIRT gene expression that was tissue-specific for each SIRT. This was evidenced by multivariate analyses, which established two main clusters corresponding to SIRTs with relatively high (SIRT1, 2, and 5) and low (SIRT3, 4, 6, and 7) gene expression levels. A nutritional regulation was also evidenced in 10-day fasted fish, and SIRT2–4 exhibited an overall downregulated expression. SIRT1, 5, 6, and 7 were mostly upregulated, although clustering analyses evidenced a highly regulated response that was different for each SIRT according to the different tissue metabolic capabilities. These findings supported the use of SIRTs alone or in combination with other biomarkers for the metabolic phenotyping of farmed fish and gilthead sea bream in particular, This study was funded by the European Union (ARRAINA, FP7-KBBE-2011-5-288925, Advanced research initiatives for nutrition and aquaculture). The views expressed in this work are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission. Additional funding was obtained from the Spanish MINECO (MI2-Fish, AGL2013-48560) and from Generalitat Valenciana (PROMETEO FASE II-2014/085).

A metabolomic study has been performed to identify sensitive and robust biomarkers of malnutrition in farmed fish, using gilthead sea bream (Sparus aurata) as a model. The metabolomic fingerprinting of serum from fasted fish was assessed by means of ultra-high performance liquid chromatography coupled to quadrupole time-offlight mass spectrometry. More than 15,000 different m/z ions were detected and Partial Least Squares–Discriminant analysis allowed a clear differentiation between the two experimental groups (fed and 10-day fasted fish) with more than 90% of total variance explained by the two first components. The most significant metabolites (up to 45) were elucidated on the basis of their tandem mass spectra with a broad representation of amino acids, oligopeptides, urea cycle metabolites, L-carnitinerelated metabolites, glutathione-related metabolites, fatty acids, lysophosphatidic acids, phosphatidylcholines as well as biotin- and noradrenaline-related metabolites. This untargeted approach highlighted important adaptive responses in energy and oxidative metabolism, contributing to identify robust and nutritionally-regulated biomarkers of health and metabolic condition that will serve to assess the welfare status of farmed fish., This work was supported by the Spanish MINECO (MI2-Fish, AGL2013-48560) and Plà de promoció de la investigació de la Universitat Jaume I (P1•1B2015-59) and the Generalitat Valenciana as research group of excellence (PROMETEO II/2014/023, PROMETEO II/2014/085, Collaborative Research on Environment and Food-Safety, ISIC/2012/016).

The skin mucus of gilthead sea bream was mapped by one-dimensional gel electrophoresis followed by liquid chromatography coupled to high resolution mass spectrometry using a quadrupole time-of-flight mass analyzer. More than 2,000 proteins were identified with a protein score filter of 30. The identified proteins were represented in 418 canonical pathways of the Ingenuity Pathway software. After filtering by canonical pathway overlapping, the retained proteins were clustered in three groups. The mitochondrial cluster contained 59 proteins related to oxidative phosphorylation and mitochondrial dysfunction. The second cluster contained 79 proteins related to antigen presentation and protein ubiquitination pathways. The third cluster contained 257 proteins where proteins related to protein synthesis, cellular assembly, and epithelial integrity were over-represented. The latter group also included acute phase response signaling. In parallel, two-dimensional gel electrophoresis methodology identified six proteins spots of different protein abundance when comparing unstressed fish with chronically stressed fish in an experimental model that mimicked daily farming activities. The major changes were associated with a higher abundance of cytokeratin 8 in the skin mucus proteome of stressed fish, which was confirmed by immunoblotting. Thus, the increased abundance of markers of skin epithelial turnover results in a promising indicator of chronic stress in fish., This study was funded by the European Union (AQUAEXCEL, FP7/2007/2013; grant agreement No. 262336, Aquaculture infrastructures for excellence in European fish research) project. The views expressed in this work are the sole responsibility of the authors and do not necessarily reflect the views of the European Commission. Additional funding was obtained from the Spanish Ministerio de Economía y Competitividad (MI2-Fish, AGL2013-48560) and from Generalitat Valenciana (PROMETEO FASE II-2014/085). Proteomics study was done at Proteomics laboratory of University of Valencia, Spain (SCSIE). This laboratory is a member of Proteored, PRB2-ISCIII and is supported by grant PT13/0001, of the PE I+D+i 2013–2016, funded by Instituto de Salud Carlos III and Fondo Europeo de Desarrollo Regional (FEDER).

[Background]: The constant increase of aquaculture production and wealthy seafood consumption has forced the industry to explore alternative and more sustainable raw aquafeed materials, and plant ingredients have been used to replace marine feedstuffs in many farmed fish. The objective of the present study was to assess whether plant-based diets can induce changes in the intestinal mucus proteome, gut autochthonous microbiota and disease susceptibility of fish, and whether these changes could be reversed by the addition of sodium butyrate to the diets. Three different trials were performed using the teleostean gilthead sea bream (Sparus aurata) as model. In a first preliminary short-term trial, fish were fed with the additive (0.8%) supplementing a basal diet with low vegetable inclusion (D1) and then challenged with a bacteria to detect possible effects on survival. In a second trial, fish were fed with diets with greater vegetable inclusion levels (D2, D3) and the long-term effect of sodium butyrate at a lower dose (0.4%) added to D3 (D4 diet) was tested on the intestinal proteome and microbiome. In a third trial, the long-term effectiveness of sodium butyrate (D4) to prevent disease outcome after an intestinal parasite (Enteromyxum leei) challenge was tested. [Results]: The results showed that opposed forces were driven by dietary plant ingredients and sodium butyrate supplementation in fish diet. On the one hand, vegetable diets induced high parasite infection levels that provoked drops in growth performance, decreased intestinal microbiota diversity, induced the dominance of the Photobacterium genus, as well as altered the gut mucosal proteome suggesting detrimental effects on intestinal function. On the other hand, butyrate addition slightly decreased cumulative mortality after bacterial challenge, avoided growth retardation in parasitized fish, increased intestinal microbiota diversity with a higher representation of butyrate-producing bacteria and reversed most vegetable diet-induced changes in the gut proteome. [Conclusions]: This integrative work gives insights on the pleiotropic effects of a dietary additive on the restoration of intestinal homeostasis and disease resilience, using a multifaceted approach., This work has been carried out with financial support from the European Union under grant projects ARRAINA (FP7-KBBE-2011-288,925) to JPS, MP and VK and ParaFishControl (H2020-634429) to ASB. Additional funding has been received from Spanish Ministry of Economy and Competitiveness (MINECO) project no. AGL2013- 48560-R to JPS and ASB, and Generalitat Valenciana (PROMETEOII/2014/085) to ASB. MCP was contracted under CSIC PIE project no. 201740E013 and MINECO FPDI-2013-15741, and IE under APOSTD/2016/037 grant by the “Generalitat Valenciana”., We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

Four isoproteic/isolipidic plant protein-based diets were formulated to assess the lasting effects of feed additives and low fish meal (FM) and fish oil (FO) diet formulations on gilthead sea bream growth performance. FM was included at 23% in the control diet (D1) and at 3% in the other three diets (D2, D3, D4). Added oil was either FO (D1) or a blend of vegetable oils replacing 58% (D2) and 84% (D3, D4 diets) of FO. A commercial sodium butyrate preparation (NOREL, 70-BP) was added to the D4 diet at 0.4%. Each diet was allocated to triplicate groups of juvenile fish fed to satiety over an 8-month feeding trial (May-December). All fish grew efficiently from 15. g of initial body weight to 296-320. g with an overall feed efficiency (FE) of 0.95-1.01, although fish fed D3 and D4 diets showed transient growth impairments over the course of the first four weeks of the trial. Data on biometric indexes, whole body composition, haematology and blood biochemistry revealed a strong effect of sampling time in fish sampled at mid-summer (August) and late autumn (December). In contrast, the diet effect was mostly reduced to a few blood parameters. Low inclusion levels of FM reduced plasma haemoglobin levels (D2, D3), but these effects were reversed by butyrate supplementation (D4). The same phenomena occurred for total cholesterol with the highest circulating concentration of choline and IGF-I in fish fed the D4 diet during their summer growth spurt. At the transcriptional level, gene expression profiling of liver and skeletal muscle with a PCR-array of 87 growth markers provided additional evidence for an overall well-growth condition in all of the experimental groups. Up to 73 genes were found at detectable levels in the liver tissue, but only 13 were differentially expressed. Likewise, 84 genes were actively transcribed in the skeletal muscle, but only nine were differentially expressed in at least one experimental group. Butyrate supplementation reversed the up-regulated expression of inflammatory cytokines (TNFα) and muscle markers of cellular morphogenesis and protein breakdown (CDH15, CAPN3, PSMA5, PSMB1, UBE2N) in the muscle of fish fed the extreme D3 diet. These results support the use of low FM/FO diets alone or supplemented with feed additives, which have the potential to improve or reverse metabolic steady-states. Statement of relevance: Butyrate effect on low fish meal/fish oil diets., This study was funded by the European Union (ARRAINA, FP7-KBBE-2011-5-288925, Advanced research initiatives for nutrition and aquaculture) projects. Additional funding was obtained from the Spanish MINECO (MI2-Fish, AGL2013-48560) and from Generalitat Valenciana (PROMETEO FASE II-2014/085).

High-quality sequencing reads from the intestine of European sea bass were assembled, annotated by similarity against protein reference databases and combined with nucleotide sequences from public and private databases. After redundancy filtering, 24,906 non-redundant annotated sequences encoding 15,367 different gene descriptions were obtained. These annotated sequences were used to design a custom, high-density oligo-microarray (8 × 15 K) for the transcriptomic profiling of anterior (AI), middle (MI), and posterior (PI) intestinal segments. Similar molecular signatures were found for AI and MI segments, which were combined in a single group (AI-MI) whereas the PI outstood separately, with more than 1900 differentially expressed genes with a fold-change cutoff of 2. Functional analysis revealed that molecular and cellular functions related to feed digestion and nutrient absorption and transport were over-represented in AI-MI segments. By contrast, the initiation and establishment of immune defense mechanisms became especially relevant in PI, although the microarray expression profiling validated by qPCR indicated that these functional changes are gradual from anterior to posterior intestinal segments. This functional divergence occurred in association with spatial transcriptional changes in nutrient transporters and the mucosal chemosensing system via G protein-coupled receptors. These findings contribute to identify key indicators of gut functions and to compare different fish feeding strategies and immune defense mechanisms acquired along the evolution of teleosts., This work was funded by the EU seventh Framework Programme by the ARRAINA (Advanced Research Initiatives for Nutrition and Aquaculture; KBBE-2011-288925) project. It does not necessarily reflect the views of the EU and in no way anticipates the Commission's future policy in this area. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Additional funding was obtained from the Spanish Ministerio de Economía y Competitividad through the MI2-FISH project (Unraveling Metabolic, Intestinal and Immunopathological Fish Status; AGL2013-48560) and Generalitat Valenciana (PROMETEO FASE II-2014/085).

There is a constant need to find feed additives that improve health and nutrition of farmed fish and lessen the intestinal inflammation induced by plant-based ingredients. The objective of this study was to evaluate the effects of adding an organic acid salt to alleviate some of the detrimental effects of extreme plant-ingredient substitution of fish meal (FM) and fish oil (FO) in gilthead sea bream diet. Three experiments were conducted. In a first trial (T1), the best dose (0.4%) of sodium butyrate (BP-70 ®NOREL) was chosen after a short (9-weeks) feeding period. In a second longer trial (T2) (8 months), four diets were used: a control diet containing 25% FM (T2-D1) and three experimental diets containing 5% FM (T2-D2, T2-D3, T2-D4). FO was the only added oil in D1, while a blend of plant oils replaced 58% and 84% of FO in T2-D2, and T2-D3 and T2-D4, respectively. The latter was supplemented with 0.4% BP-70. In a third trial (T3), two groups of fish were fed for 12 and 38 months with D1, D3 and D4 diets of T2. The effects of dietary changes were studied using histochemical, immunohistochemical, molecular and electrophysiological tools. The extreme diet (T2-D3) modified significantly the transcriptomic profile, especially at the anterior intestine, up-regulating the expression of inflammatory markers, in coincidence with a higher presence of granulocytes and lymphocytes in the submucosa, and changing genes involved in antioxidant defences, epithelial permeability and mucus production. Trans-epithelial electrical resistance (Rt) was also decreased (T3-D3). Most of these modifications were returned to control values with the addition of BP-70. None of the experimental diets modified the staining pattern of PCNA, FABP2 or ALPI. These results further confirm the potential of this additive to improve or reverse the detrimental effects of extreme fish diet formulations, This work has been carried out with financial support from the European Commission of the European Union, specific RTD Framework Programme 7, (FP7/2007-2013) under grant projects ARRAINA (KBBE-2011-288925) to JPS, AO and VK, AQUAEXCEL (262336) under TNA project 0044/03/04/14a to FG, and AQUAEXCEL2020 (652831) under TNA project 0004/01-INTEBREAM to JF. This publication reflects the views only of the authors, and the European Commission cannot be held responsible for any use which may be made of the information contained therein. JF was also funded by the Portuguese Foundation for Science and Technology (FCT) through Project PTDC/MARBIO/3034/2014. CCMar was supported by national funds from FCT through institutional project UID/Multi/04326/2013. Additional funding has been received by Spanish Ministry of Economy and Competitiveness (MINECO) project no. AGL2013-48560-R to JPS and ASB, and Generalitat Valenciana (PROMETEOII/2014/085) to ASB. JAMS received a Postdoctoral Research Fellow (Juan de la Cierva-Formación, Reference FJCI-2014-20161) from MINECO.

Background. The increased demand for fish protein has led to the intensification of aquaculture practices which are hampered by nutritional and health factors affecting growth performance. To solve these problems, antibiotics have been used for many years in the prevention, control and treatment against disease as well as growth promoters to improve animal performance. Nowadays, the use of antibiotics in the European Union and other countries has been completely or partially banned as a result of the existence of antibiotic cross-resistance. Therefore, a number of alternatives, including enzymes, prebiotics, probiotics, phytonutrients and organic acids used alone or in combination have been proposed for the improvement of immunological state, growth performance and production in livestock animals. The aim of the present study was to evaluate two commercially available feed additives, one based on medium-chain fatty acids (MCFAs) from coconut oil and another with a Bacillus-based probiotic, in gilthead sea bream (GSB, Sparus aurata), a marine farmed fish of high value in the Mediterranean aquaculture. Methods. The potential benefits of adding two commercial feed additives on fish growth performance and intestinal health were assessed in a 100-days feeding trial. The experimental diets (D2 and D3) were prepared by supplementing a basal diet (D1) with MCFAs in the form of a sodium salt of coconut fatty acid distillate (DICOSAN R ; Norel, Madrid, Spain), rich on C-12, added at 0.3% (D2) or with the probiotic Bacillus amyloliquefaciens CECT 5940, added at 0.1% (D3). The study integrated data on growth performance, blood biochemistry, histology and intestinal gene expression patterns of selected markers of intestinal function and architecture. Results. MCFAs in the form of a coconut oil increased feed intake, growth rates and the surface of nutrient absorption, promoting the anabolic action of the somatotropic axis. The probiotic (D3) induced anti-inflammatory and anti-oxidant effects with changes in circulating cortisol, immunoglobulin M, leukocyte respiratory burst, and mucosal expression levels of cytokines, lymphocyte markers and immunoglobulin T. Discussion. MCFA supplementation showed positive effects on GSB growth and intestinal architecture acting mainly in the anterior intestine, where absorption takes place. The probiotic B. amyloliquefaciens CECT 5940 exhibited key effects in the regulation of the immune status inducing anti-inflammatory and anti-oxidant effects which can be potentially advantageous upon infection or exposure to other stressors. The potential effects of these feed additives in GSB are very promising to improve health and disease resistance in aquaculture., Spanish MINECO: AGL2013-48560-R. ., Generalitat Valenciana: PROMETEO-FASE II/2014/085., MINECO: FPDI-2013-15741., CSIC PIE: 201740E013

A custom microarray was used for the transcriptomic profiling of liver, gills and hypothalamus in response to hypo- (38‰ → 5‰) or hyper- (38‰ → 55‰) osmotic challenges (7 days after salinity transfer) in gilthead sea bream (Sparus aurata) juveniles. The total number of differentially expressed genes was 777. Among them, 341 and 310 were differentially expressed in liver after hypo- and hyper-osmotic challenges, respectively. The magnitude of changes was lower in gills and hypothalamus with around 131 and 160 responsive genes in at least one osmotic stress condition, respectively. Regardless of tissue, a number of genes were equally regulated in either hypo- and hyper-osmotic challenges: 127 out of 524 in liver, 11 out of 131 in gills and 19 out of 160 in hypothalamus. In liver and gills, functional analysis of differentially expressed genes recognized two major clusters of overlapping canonical pathways that were mostly related to “Energy Metabolism” and “Oxidative Stress”. The later cluster was represented in all the analyzed tissues, including the hypothalamus, where differentially expressed genes related to “Cell and tissue architecture” were also over-represented. Overall the response for “Energy Metabolism” was the up-regulation, whereas for oxidative stress-related genes the type of response was highly dependent of tissue. These results support common and different osmoregulatory responses in the three analyzed tissues, helping to load new allostatic conditions or even to return to basal levels after hypo- or hyper-osmotic challenges according to the different physiological role of each tissue., This research was funded by the Spanish Ministry of Economic Affairs and Competitiveness (MINECO) with FEDER/ERDF contribution by projects AGL2013-48835-C2-1-R to JMM and AQUAGENOMICS (CDS2007-00002) to MY and JPS. JAMS is supported by a Post-Doctoral contract (Juan de la Cierva-formación, Reference FJCI-2014-20161) from Spanish Ministry of Economic Affairs and Competitiveness (MINECO).