Short-term, but not long-term feed restriction causes differential expression of leptins in Atlantic salmon

Atlantic salmon was used to investigate the effect of long- and short-term dietary ration on the tissue expression levels of leptins. Compared to ad libitum fed fish (0.8-3kg), 6months of dietary restriction (60%) resulted in significantly lower body mass and adiposity, but did not produce a clear effect on the expression levels of either lepa1 or lepa2. For visceral adipose tissue, however, the long-term data indicated that season appeared to influence the levels of lepa1 expression of ad libitum fed fish, but not feed-restricted fish. By comparing the total levels of leptin mRNA expression to the tissue lipid contents, we found that only white muscle lepa1 showed the positive relation reported in mammals. The existence of a postprandial leptin response in Atlantic salmon parr was determined in fed and unfed parr over a 24h period. In contrast to other animals, lepa1 peaked in the unfed fish, initially in the white muscle at 6h, and subsequently in belly flap, liver and visceral adipose tissue at 9h. Only lepa2 in the visceral adipose tissue of fed fish showed a similar 9h peak, but at an order of magnitude lower than lepa1 in the unfed fish. These data reveal that short-term feed restriction causes a latent (6-9h) upregulation of lepa-type genes in the fatty tissues of Atlantic salmon, a finding that contrasts the mammalian response.

Leptin in fish: possible role in sexual maturation in male Atlantic salmon

Leptin plays an important role in energy homeostasis and reproductive function in mammals, while its function in fish is still poorly understood, especially its role in reproduction. In the present study, leptin gene expression and circulating leptin plasma levels were measured during sexual maturation in male Atlantic salmon parr. In maturing male salmon, higher hepatic leptin (lepa1) gene expression levels were observed during mid-spermatogenesis compared to immature fish. An upregulation of leptin during sexual maturation has also been observed in a few other teleost species. The physiological significance of elevated leptin levels during the maturational process in teleosts remains to be explored.

Intestinal fatty acid binding protein (fabp2) in Atlantic salmon (Salmo salar): Localization and alteration of expression during development of diet induced enteritis

In the present study full-length cDNAs corresponding to three isoforms of intestinal fatty acid binding protein (fabp2) in Atlantic salmon were cloned and characterized. Gene expression of fabp2 was observed in all tissues investigated, although differences were observed between isoforms. The highest fabp2a1, fabp2a2, and fabp2b expression was in the intestine. A 15kDa protein, corresponding to putative Fabp2 protein, was identified by immunoblotting using anti-human Fabp2 antibody. Immunoblotting and immunohistochemistry confirmed that Fabp2 protein was present in most Atlantic salmon tissues. Similar to gene expression, intestinal tissues had the highest Fabp2 protein levels, decreasing gradually from proximal to distal intestine. During development of distal intestinal inflammation caused by dietary soybean meal from 0 to 21days, Fabp2 decreased significantly on both transcriptional and protein levels. The reduction in Fabp2 was preceded by a down regulation of peroxisome proliferator activated receptor (ppar) alpha and gamma, fabp2's presumed regulatory proteins, and followed by a progressive increase in proliferating cell nuclear antigen (Pcna) staining. Results illustrate that the early decline of distal intestinal fabp2 was likely caused by a down regulation of their regulatory proteins, but at later time points reduced Fabp2 may largely be due to a less mature enterocyte population resulting from rapid cell turnover.

MULAN related gene (MRG): a potential novel ubiquitin ligase activator of NF-kB involved in immune response in Atlantic salmon (Salmo salar)

Nuclear factor-kB (NF-kB) is a transcription factor that plays a central role in the regulation of a variety of genes including many involved in bacterial and viral infections. NF-kB is normally sequestered by inhibitory proteins (IkBs) in the cytoplasm of non-stimulated cells. The degradation of IkBs by the ubiquitin proteasome pathway releases NF-kB allowing its translocation to the nucleus where it regulates gene transcription. The Mitochondrial Ubiquitin Ligase Activator of NF-kB, (MULAN), is an E3 ubiquitin ligase involved in controlling activation of NF-kB, and regulating mitochondrial dynamics and apoptosis. We report the characterisation of a novel piscine-specific MULAN related gene (MRG) sequence, its mRNA tissue distribution and expression following in vivo and in vitro challenges. MRG cDNA was identified in Atlantic salmon and its sequence encodes a predicted protein of 274 amino acids. The mRNA of MRG was expressed in multiple tissues, with the highest abundance head kidney. An Aeromonas salmonicida bacterial challenge increased expression of this gene in head kidney, liver and gill tissue at 6 h and 24 h. In vitro stimulation of a salmonid cell line indicated MRG was increased in expression following stimulation with LPS, PolyI:C and recombinant trout IL-1β for 4 h and 24 h. These results suggest an active role of MRG in the activation of the NF-kB pathway during early immune responses.

The effect of nonylphenol on gene expression in Atlantic salmon smolts

The parr-smolt transformation in Atlantic salmon (Salmo salar) is a complex developmental process that culminates in the ability to migrate to and live in seawater. Exposure to environmental contaminants like nonylphenol can disrupt smolt development and may be a contributing factor in salmon population declines. We used GRASP 16K cDNA microarrays to investigate the effects of nonylphenol on gene expression in Atlantic salmon smolts. Nonylphenol exposure reduced gill Na(+)/K(+)-ATPase activity and plasma cortisol and triiodothyronine levels. Transcriptional responses were examined in gill, liver, olfactory rosettes, hypothalamus, and pituitary. Expression of 124 features was significantly altered in the liver of fish exposed to nonylphenol; little to no transcriptional effects were observed in other tissues. mRNA abundance of genes involved in protein biosynthesis, folding, modification, transport and catabolism; nucleosome assembly, cell cycle, cell differentiation, microtubule-based movement, electron transport, and response to stress increased in nonylphenol-treated fish. This study expands our understanding of the effect of nonylphenol on smolting and provides potential targets for development of biomarkers.

Exploring the transcriptome of Atlantic salmon (Salmo salar) skin, a major defense organ

The skin of fish is the first line of defense against pathogens and parasites. The skin transcriptome of the Atlantic salmon is poorly characterized, and currently only 2,089 expressed sequence tags (ESTs) out of a total of half a million sequences are generated from skin-derived cDNA libraries. The primary aim of this study was to enhance the transcriptomic knowledge of salmon skin by using next-generation sequencing (NGS) technology, namely the Roche-454 platform. An equimolar mixture of high-quality RNA from skin and epidermal samples of salmon reared in either freshwater or seawater was used for 454-sequencing. This technique yielded over 600,000 reads, which were assembled into 34,696 isotigs using Newbler. Of these isotigs, 12 % had not been sequenced in Atlantic salmon, hence representing previously unreported salmon mRNAs that can potentially be skin-specific. Many full-length genes have been acquired, representing numerous biological processes. Mucin proteins are the main structural component of mucus and we examined in greater detail the sequences we obtained for these genes. Several isotigs exhibited homology to mammalian mucins (MUC2, MUC5AC and MUC5B). Mucin mRNAs are generally >10 kbp and contain large repetitive units, which pose a challenge towards full-length sequence discovery. To date, we have not unearthed any full-length salmon mucin genes with this dataset, but have both N- and C-terminal regions of a mucin type 5. This highlights the fact that, while NGS is indeed a formidable tool for sequence data mining of non-model species, it must be complemented with additional experimental and bioinformatic work to characterize some mRNA sequences with complex features.

Stress and expression of cyclooxygenases (cox1, cox2a, cox2b) and intestinal eicosanoids, in Atlantic salmon, Salmo salar L

Prostaglandin H synthetases (cyclooxygenases) catalyze the initial reactions leading to prostanoids in animals. They form interesting links between diet and fish physiology as the type and nature of eicosanoids are affected by dietary lipid sources. Their expression is likely to be affected by tissues and environmental conditions leading to altered amount and ratio of eicosanoids. These mechanisms are, however, poorly understood in fish. In the present study, Atlantic salmon Salmo salar L. (1,000 g, 10°C, seawater) were subjected to acute chasing stress. Liver, kidney, spleen, gill, muscle, midgut and hindgut were extracted before and 1 h post-stress and analyzed for mRNA expression of cox1, cox2a and cox2b. Intestinal samples were further sampled over 24 h for both cox expression and analysis of 15 eicosanoids and isoprostanes of the n-3 and n-6 series. Results show a highly variable but consecutively expression of cox1, cox2a and cox2b in most of the tissues analyzed. Low levels were only found for cox2a in liver and cox2b in liver and kidney. The study reveals the general trend that cox1 is about 10 times the level of cox2b, which again is about 10 times the level of cox2a. Cox2b shows the highest level of expression in the gills indicating a possible higher requirement for this protein in gills. Imposing stress to the fish induces a temporal increase in the expression of cox2a in the midgut, while the gene expression of the other genes is not affected in any of the tissues analyzed. There is, however, a general tendency to increased expression of both cox2 genes that merits further studies. Stress had a profound effect on the intestinal eicosanoid content which showed a general decrease in midgut sections after stress that persisted for at least 24 h.

Interaction of soyasaponins with plant ingredients in diets for Atlantic salmon, Salmo salar L

The effects of combining soyasaponins with plant ingredients on intestinal function and fish health were investigated in an 80 d study with Atlantic salmon (270 g) distributed thirty each into twenty-four tanks with seawater. Soyasaponins were supplemented (2 g/kg) to diets with maize gluten (MG), pea protein concentrate (PPC) and sunflower (SFM), rapeseed (RSM) or horsebean meals. A diet with soyabean meal (SBM) and another with wheat gluten and soyasaponins served as reference diets. Marked soyasaponin effects were observed when combined with PPC. This combination induced inflammation in the distal intestine (DI) similar to SBM, reduced feed intake, apparent digestibility of lipid, most amino acids and ash, decreased bile salt levels in intestinal chyme and decreased leucine aminopeptidase (LAP) activity but increased trypsin activity in the DI. No enteritis was observed in other diet groups, but small consistent negative soyasaponin effects were seen on lipid and fatty acid digestibility, faecal DM and LAP activity of the DI. Soyasaponin combination with RSM reduced digestibility of all nutrients including minerals. The mineral effect was also seen for SFM, whereas with MG and SFM a positive soyasaponin effect on feed intake was observed. Caution should be exercised to avoid ingredient combinations giving high saponin levels, a condition that appears to be a key factor in diet-induced enteritis together with certain plant ingredients.

Dechlorination of the dietary nona-chlorinated toxaphene congeners 62 and 50 into the octa-chlorinated toxaphene congeners 44 and 40 in zebrafish (Danio rerio) and Atlantic salmon (Salmo salar)

The relative feed-to-fish accumulation and possible biotransformation of the nona-chlorinated toxaphene congeners currently included in EU-legislation (CHB-50 and -62) and the octa-chlorinated congeners recommended by the European Food Safety Authority to be included in future surveillance of fish samples (CHB-40, 41, and 44) were investigated in the present study. Model fish Danio rerio were fed either (a) diets spiked with a combination as well as the pure individual toxaphene congeners CHB-50 or 62 or (b) diets spiked with the combination of CHB ∑50+62 and/or CHB ∑40+41+44. In addition, seawater adapted Atlantic salmon smolts were fed technical toxaphene enriched feeds for 62 days. Zebrafish fed a diet containing CHB-50 and CHB-62 accumulated newly formed CHB-40&41 and CHB-44, respectively. The biomagnifications factors (BMF) of the toxaphene congeners in Atlantic salmon muscle from the feeds spiked with technical toxaphene were significantly correlated with their relative lipophilicity (expressed as logK(ow)). An exception was CHB-44 which had a higher BMF than could be expected from its specific logK(ow), reflecting that CHB-44 is a metabolite formed under dietary exposure to CHB-62. This paper reports the in vivo dechlorination of nona-chlorinated toxaphene congeners into octa-chlorinated congeners in feeding trials with a model fish (zebrafish) and an oily food fish (Atlantic salmon).

Pigments, parasites and personalitiy: towards a unifying role for steroid hormones?

A surging interest in the evolution of consistent trait correlations has inspired research on pigment patterns as a correlate of behavioural syndromes, or “animal personalities”. Associations between pigmentation, physiology and health status are less investigated as potentially conserved trait clusters. In the current study, lice counts performed on farmed Atlantic salmon Salmo salar naturally infected with ectoparasitic sea lice Lepeophtheirus salmonis showed that individual fish with high incidence of black melanin-based skin spots harboured fewer female sea lice carrying egg sacs, compared to less pigmented fish. There was no significant association between pigmentation and lice at other developmental stages, suggesting that host factors associated with melanin-based pigmentation may modify ectoparasite development to a larger degree than settlement. In a subsequent laboratory experiment a strong negative correlation between skin spots and post-stress cortisol levels was revealed, with less pigmented individuals showing a more pronounced cortisol response to acute stress. The observation that lice prevalence was strongly increased on a fraction of sexually mature male salmon which occurred among the farmed fish further supports a role for steroid hormones as mediators of reduced parasite resistance. The data presented here propose steroid hormones as a proximate cause for the association between melanin-based pigmentation and parasites. Possible fundamental and applied implications are discussed.

Biomagnification of organohalogens in Atlantic salmon (Salmo salar) from its main prey species in three areas of the Baltic Sea

Factors affecting the biomagnification of organohalogens in Baltic salmon from sprat, herring and three-spined stickleback were assessed in three feeding areas. Second sea-year salmon contained (in fresh weight of whole fish) 79-250ngg(-1) polychlorinated biphenyls (ΣPCB), 0.9-2.7pgg(-1) dibenzo-p-dioxins (ΣPCDD), 8-19pgg(-1) dibenzofurans (ΣPCDF), 96-246pgg(-1) coplanar PCBs, 2.4-3.6ngg(-1) polybrominated diphenylethers (ΣPBDE), and 39-136ngg(-1) Σ(indicator) PCB6. The EU limits for WHO toxic equivalent concentrations in fish feed were already exceeded in one-year-old sprat and herring and were exceeded many-fold in older age groups. The differences in the biomagnification rates of organohalogens in salmon appeared to be related to the feeding area, principal prey species, and the fat content and growth rate of the prey species.

[Dynamics of fatty acid composition of total lipids during embryonic development of Atlantic salmon Salmo salar L]

Dynamics of fatty acid composition of total lipids was studied for freshwater salmon Salmo salar L. during its embryonic development from blastula (3 hours) up to hatching (108 days) as well as in unfertilized eggs. Stable amount of total and some saturated, monounsaturated and polyunsaturated fatty acids (PUFA) of total lipids was observed during embryonic development. Considerable changes in fatty acid composition were observed at the stage of prelarvae hatching, i.e., significant decrease of (n-6) PUFA (18:2(n-6) and 20:4(n-6)) and (n-3) PUFA and increase of total and some saturated and monounsaturated fatty acids was registered. Change in saturation ratio of membrane lipids justifies the presence of the biochemical mechanism forwarded on regulation of cell membrane enzymes in accordance with the changes of internal physiological processes taking place in the organism and fluctuations of external environmental conditions or the preparation period (as reproduction). Data on peculiarities of transformation and utilization of fatty acids during salmon embryonic development may be used for understanding of their functional role in the developing organism as well as for assessing the quality of the caviar.

Changes in patterns of persistent halogenated compounds through a pelagic food web in the Baltic Sea

The concentrations and patterns of persistent halogenated compounds (PHCs), including polychlorinated biphenyls (PCBs), DDT, hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB) and polybrominated diphenyl ethers (PBDEs) were examined in a pelagic food web from the southern Baltic Sea consisting of sediment, zooplankton, sprat, Atlantic salmon and anadromous brown trout. Lipid-normalized concentrations generally increased from low trophic levels to high trophic levels, with the exception of HCHs. Due to high concentrations of PBDEs in some zooplankton samples, biomagnification of BDE-47 was only observed for salmon/sprat and trout/sprat. Sprat collected individually and from salmon stomach had significantly different lipid-normalized concentrations and varied in their PHC pattern as well, possibly indicating a large natural variation within the Baltic Sea. The highest lipid-normalized concentrations were found in brown trout. Salmon and brown trout were similar in their PHC pattern suggesting similar food sources. Variation in PHC patterns among trophic levels was not smaller than that among geographically distinct locations, confirming the importance of comparable trophic levels for the assessment of PHC patterns, e.g. for tracing migratory fish.

The role of Δ6-desaturase acyl-carrier specificity in the efficient synthesis of long-chain polyunsaturated fatty acids in transgenic plants

The role of acyl-CoA-dependent Δ6-desaturation in the heterologous synthesis of omega-3 long-chain polyunsaturated fatty acids was systematically evaluated in transgenic yeast and Arabidopsis thaliana. The acyl-CoA Δ6-desaturase from the picoalga Ostreococcus tauri and orthologous activities from mouse (Mus musculus) and salmon (Salmo salar) were shown to generate substantial levels of Δ6-desaturated acyl-CoAs, in contrast to the phospholipid-dependent Δ6-desaturases from higher plants that failed to modify this metabolic pool. Transgenic plants expressing the acyl-CoA Δ6-desaturases from either O. tauri or salmon, in conjunction with the two additional activities required for the synthesis of C20 polyunsaturated fatty acids, contained higher levels of eicosapentaenoic acid compared with plants expressing the borage phospholipid-dependent Δ6-desaturase. The use of acyl-CoA-dependent Δ6-desaturases almost completely abolished the accumulation of unwanted biosynthetic intermediates such as γ-linolenic acid in total seed lipids. Expression of acyl-CoA Δ6-desaturases resulted in increased distribution of long-chain polyunsaturated fatty acids in the polar lipids of transgenic plants, reflecting the larger substrate pool available for acylation by enzymes of the Kennedy pathway. Expression of the O. tauriΔ6-desaturase in transgenic Camelina sativa plants also resulted in the accumulation of high levels of Δ6-desaturated fatty acids. This study provides evidence for the efficacy of using acyl-CoA-dependent Δ6-desaturases in the efficient metabolic engineering of transgenic plants with high value traits such as the synthesis of omega-3 LC-PUFAs.

Muscle-specific RING finger (MuRF) cDNAs in Atlantic salmon (Salmo salar) and their role as regulators of muscle protein degradation

The selection of proteins destined for degradation by the ubiquitin-proteasome pathway is coordinated by E3 ubiquitin ligases (E3Ub). One group of E3Ubs is described as muscle-specific RING finger (MuRF) molecules. In mammals, these proteins are believed to be central to targetting of muscle proteins for degradation during physiological perturbations such as starvation and inflammatory responses. In fish, the diversity of MuRF sequences is unexplored as is the expression of their mRNAs. In this study, three MuRF1 cDNAs, denoted as MuRF1a, MuRF1b, and MuRF1c, and a single MuRF2 were identified and characterized in Atlantic salmon. The MuRF1 sequences are highly conserved and encode predicted proteins of 349, 350, and 353 amino acids, whereas MuRF2 encodes a longer protein of 462 amino acids. The evolutionary relationship of these sequences with other fish and mammalian molecules shows that MuRF1a and 1b may have arisen from a recent salmonid duplication. The mRNA of MuRFs was expressed in multiple tissues, with highest abundance in white muscle tissue followed by the heart. The expression of MuRFs was modulated after both starvation and immune challenge. Starvation increased expression of all MuRF mRNAs in white muscle, with the greatest increase found in MuRF1a. A proinflammatory stimulation increased expression of MuRF mRNA in muscle and other tissues indicating a role of these proteins in protein degradation during inflammation.

Dietary methylmercury alters the proteome in Atlantic salmon (Salmo salar) kidney

BACKGROUND

Methylmercury (MeHg) is an environmental contaminant most known for its severe neurotoxic effects. Although accumulation of MeHg tends to be several folds higher in kidney compared to other tissues, studies on nephrotoxic effects are almost non-existing. In this study we aim to investigate the toxicity of dietary MeHg in kidney of Atlantic salmon (Salmo salar).

MATERIAL AND METHODS

Atlantic salmon were exposed to dietary MeHg for a period of 8 weeks, before the fish were euthanized and kidney was sampled for proteomic and real time RT-PCR analysis, as well as for mercury determination. Protein separation was done with 2-D PAGE, and differentially regulated spots were picked for analysis using liquid chromatography MS/MS analysis. Moreover, whole blood and liver tissue were sampled for mercury determination and real time RT-PCR (liver).

RESULTS

MeHg exposed fish accumulated significantly more mercury (Hg) than control fish. The proteomic analysis revealed differential abundance of 26 spots in the kidney, and 14 of these protein spots were successfully identified. The proteins identified indicated effects of MeHg on; metabolism, inflammation, oxidative stress, protein-folding, and cell-structural components. Gene expression analysis of selected markers revealed few differentially regulated transcripts in kidney and liver in the exposed fish compared to the control fish. However, the affected transcripts indicated a disruption in the expression of two metabolic markers due to MeHg exposure in liver.

CONCLUSION

This study suggests that dietary MeHg has similar effects in kidney as previously shown for other tissues in fish. The effects observed were in markers for oxidative stress, inflammation and energy metabolism. The identification of proteomic markers in this study provides a basis for a better understanding of MeHg-induced nephrotoxicity in fish.

Functional characterization and localization of a gill-specific claudin isoform in Atlantic salmon

Claudins are the major determinants of paracellular epithelial permeability in multicellular organisms. In Atlantic salmon (Salmo salar L.), we previously found that mRNA expression of the abundant gill-specific claudin 30 decreases during seawater (SW) acclimation, suggesting that this claudin is associated with remodeling of the epithelium during salinity change. This study investigated localization, protein expression, and function of claudin 30. Confocal microscopy showed that claudin 30 protein was located at cell-cell interfaces in the gill filament in SW- and fresh water (FW)-acclimated salmon, with the same distribution, overall, as the tight junction protein ZO-1. Claudin 30 was located at the apical tight junction interface and in cell membranes deeper in the epithelia. Colocalization with the α-subunit of the Na(+)-K(+)-ATPase was negligible, suggesting limited association with mitochondria-rich cells. Immunoblotting of gill samples showed lower claudin 30 protein expression in SW than FW fish. Retroviral transduction of claudin 30 into Madin-Darby canine kidney cells resulted in a decreased conductance of 19%. The decreased conductance correlated with a decreased permeability of the cell monolayer to monovalent cations, whereas permeability to chloride was unaffected. Confocal microscopy revealed that claudin 30 was expressed in the lateral membrane, as well as in tight junctions of Madin-Darby canine kidney cells, thereby paralleling the findings in the native gill. This study suggests that claudin 30 functions as a cation barrier between pavement cells in the gill and also has a general role in cell-cell adhesion in deeper layers of the epithelium.

Restoration of fillet n-3 long-chain polyunsaturated fatty acid is improved by a modified fish oil finishing diet strategy for atlantic salmon (Salmo salar L.) smolts fed palm fatty acid distillate

Reducing the lipid content in fish prior to feeding a fish oil finishing diet (FOFD) has the potential to improve n-3 long-chain (≥ C(20)) polyunsaturated fatty acid (LC-PUFA) restoration. This study had two main objectives: (1) determine whether feeding Atlantic salmon smolt a 75% palm fatty acid distillate diet (75PFAD) improves the apparent digestibility (AD) of saturated fatty acids (SFA) and (2) examine whether a food deprivation period after growth on 75PFAD leads to higher n-3 LC-PUFA restoration in the fillet when applying a FOFD. The AD of SFA was higher for 75PFAD compared to that of a fish oil (FO) diet. The relative level (as % total fatty acids (FA)) of n-3 LC-PUFA was higher in unfed fish compared to that in continuously fed fish after 21 and 28 day FOFD periods, respectively. Our results suggest that a food deprivation period prior to feeding a FOFD improves the efficiency of n-3 LC-PUFA restoration in the fillet of Atlantic salmon smolt.

Effects of long-term restricted feeding on plasma leptin, hepatic leptin expression and leptin receptor expression in juvenile Atlantic salmon (Salmo salar L.)

Leptin is a pleiotropic hormone and plays a key role in body weight regulation, energy homeostasis and lipid store utilization in mammals. In this study, we investigated the effect of feed-restriction on leptin genes (lepa1 and lepa2), leptin receptor (lepr) gene expression and plasma leptin levels in juvenile Atlantic salmon parr. Feed restriction was performed from late April to mid-June, in order to gain insight into the role of the leptin system in energy balance regulation and adiposity in juvenile salmon. A significant increase in lepa1 expression as well as higher levels of plasma leptin was found in feed-restricted fish in June compared to fully fed controls, while lepa2 gene expression decreased in both groups during the treatment period. Lepa2 was, however significantly higher in the feed-restricted group in June. Leptin receptor expression was up regulated during the period of enhanced growth and lipid deposition in the fully fed control, indicating a seasonal effect on the receptor expression in the brain. Both lepa1 and lepa2 genes very mainly expressed in the liver in juvenile salmon, while lepr was expressed in the brain but showed also considerable expression in various peripheral tissues. The study provides evidence that the leptin system is sensitive to the metabolic status of the fish as both season and restricted feeding affect lepa1 and lepa2 gene expression in the liver and brain leptin receptor expression, however, for lepa1 expression and leptin plasma level in an opposite way as that observed in the mammalian system.

Atlantic salmon (Salmo salar L.) as a net producer of long-chain marine ω-3 fatty acids

The objective of the present study was to investigate the effects of replacing high levels of marine ingredients with vegetable raw materials and with emphasis on lipid metabolism and net production of long-chain polyunsaturated ω-3 fatty acids (EPA + DHA). Atlantic salmon were fed three different replacement vegetable diets and one control marine diet before sensory attributes, β-oxidation capacity, and fatty acid productive value (FAPV) of ingested fatty acids (FAs) were evaluated. Fish fed the high replacement diet had a net production of 0.8 g of DHA and a FAPV of 142%. Fish fed the marine diet had a net loss of DHA. The present work shows that Atlantic salmon can be a net producer of marine DHA when dietary fish oil is replaced by vegetable oil with minor effects on sensory attributes and lipid metabolism.

Matrilin-1 expression is increased in the vertebral column of Atlantic salmon (Salmo salar L.) individuals displaying spinal fusions

We have previously characterized the development of vertebral fusions induced by elevated water temperature in Atlantic salmon. Molecular markers of bone and cartilage development together with histology were used to understand the complex pathology and mechanism in the development of this spinal malformation. In this study, we wanted to use proteomics, a non-hypothetical approach to screen for possible new markers involved in the fusion process. Proteins extracted from non-deformed and fused vertebrae of Atlantic salmon were therefore compared by two-dimensional electrophoresis (2DE) and MALDI-TOF analysis. Data analysis of protein spots in the 2DE gels demonstrated matrilin-1, also named cartilage matrix protein, to be the most highly up-regulated protein in fused compared with non-deformed vertebrae. Furthermore, real-time PCR analysis showed strong up-regulation of matrilin-1 mRNA in fused vertebrae. Immunohistochemistry demonstrated induced matrilin-1 expression in trans-differentiating cells undergoing a metaplastic shift toward chondrocytes in fusing vertebrae, whereas abundant expression was demonstrated in cartilaginous tissue and chordocytes of both non-deformed and fused vertebrae. These results identifies matrilin-1 as a new interesting candidate in the fusion process, and ratify the use of proteomic as a valuable technique to screen for markers involved in vertebral pathogenesis.

Lipid peroxidation and oxidative stress responses of salmon fed a diet containing perfluorooctane sulfonic- or perfluorooctane carboxylic acids

The present study was conducted to evaluate the effects of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on lipid β-oxidation and oxidative stress responses in Atlantic salmon liver and kidney tissues. We quantified changes in the expression levels of peroxisome proliferator-activated receptors (PPARs) and acyl-CoA oxidase (ACOX1) enzyme whose transcription is induced by PPARs. In addition, we analyzed gene expression patterns for enzymatic antioxidants (superoxide dismutase: SOD, catalase: CAT and glutathione peroxidase: GPx). Thiobarbituric acid reactive substances (TBARS) were analyzed as a measure for lipid peroxidation. Juvenile Atlantic salmon were repeatedly force-fed food spiked with PFOA or PFOS at 0.2mg/kg, and samples were collected after 0, 2, 5 and 8 days and after a 7 days recovery period. Our data showed that exposure of salmon to PFOS or PFOA produced changes (either increased or decreased) in mRNA expression for PPARs, ACOX1, oxidative stress responses and lipid peroxidation (TBARS) and these responses showed marked organ differences, associated with tissue bioaccumulation patterns and dependent on exposure time. Given that a classical reaction during reactive oxygen species (ROS)-induced damage involves the peroxidation of lipids, our study demonstrates that salmon continuously exposed to dietary PFOS or PFOA dose showed alteration in peroxisomal responses and oxidative stress responses, with higher severity in the kidney, compared to liver. Overall, our data suggest that ROS-mediated oxidative damage maybe a significant and putative toxic effect of PFOA and PFOS in fish as has been reported in mammals.

State diagram of salmon (Salmo salar) gelatin films

BACKGROUND

A state diagram presents different physical states of a biomaterial as a function of solid content and temperature. Despite their technological interest, little information is available on protein systems such as gelatin/water mixtures. The objective of this work was to develop state diagrams of salmon gelatin (SG) and bovine gelatin (BG) in order to determine maximal freeze concentration parameters (T'(g) , T'(m) and X(s') ) and to relate possible differences to their biochemical characteristics.

RESULTS

Biochemical characterisation of SG showed lower molecular weight and iminoacid concentration compared with BG. Likewise, the glass transition temperature (T(g) ) was lower for SG at X(s) > 0.8, which was associated with its lower molecular weight. Unexpectedly, the depression of freezing temperature (T(f) ) was greater for SG at X(s) > 0.1, which was associated with its higher ash content. Isothermal annealing produced effective values of T'(g) ≈ - 52 °C, T'(m) ≈ - 46 °C and X'(s) ≈ 0.6 for both gelatins. Interestingly, the enthalpy change associated with T'(m) (ΔH T m) was significantly higher for SG than for BG after annealing, indicating a higher proportion of ice present at about - 50 °C.

CONCLUSION

Maximal freeze concentration parameters were similar between the two gelatins, though differences in biochemical properties were evident. The results show that there are likely different ways of interaction of SG and BG with water.

Transcriptomic responses to functional feeds in Atlantic salmon (Salmo salar)

Functional feeds are diets that have positive effects on both health and growth promoting performance of the animals ingesting them, by supplying additional compounds above and beyond the basic nutritional requirements for animal growth alone. The most common additives used in aquaculture diets are probiotics, prebiotics, immunostimulants, vitamins and nucleotides. Inclusion of these components to fish diets can increase feed conversion efficiency and growth, as well as having positive effects on the fish immune system. This review discusses the results from previous studies on fish nutrition and includes a novel genomic approach, using microarray analysis, to elucidate nutritional responses in Atlantic salmon (Salmo salar) fed a newly developed functional feed health premix diet. The transcriptome analysis demonstrated that compared to the standard diet feeding with the functional feed had significant effects on biological processes in the liver. This resulted in a reduction of the expression of genes related to protein turnover, reduced circulating plasma proteins and a down regulation of genes involved in the immune response. These results suggest that the functional feed may infer a decrease in whole body metabolic demands, suppressing both protein turnover and whole body oxygen demand, as well as down regulating several genes involved in the innate immune system. Together these changes appear to result in less energy wastage in fish and an enhanced growth and performance.

Identification of the natural product 2,3,4,5-tetrabromo-1-methylpyrrole in Pacific biota, passive samplers and seagrass from Queensland, Australia

Halogenated natural products (HNPs) are frequently detected in marine organisms. High HNP concentrations have previously been found in marine mammals from the Great Barrier Reef, Australia, including in the blubber of herbivorous dugongs (Dugong dugon). To identify the source of HNPs we initially focused on the analysis of Australian seagrass (Halophila ovalis) which serves as the principal food source for dugongs. GC/MS analysis of the seagrass indicated the presence of several organobromine compounds. One compound was identified as 2,3,4,5-tetrabromo-1-methylpyrrole (TBMP) by synthesis. Subsequent analysis of semipermeable membrane devices demonstrated that the photo-sensitive TBMP is widespread in the Great Barrier Reef (Queensland, Australia). The detection of larger TBMP concentrations in fish fillets from Chile and traces in mussels from New Zealand indicated that this potential HNP may be distributed throughout the Southern Pacific Ocean.