Soya Saponins Induce Enteritis in Atlantic Salmon (Salmo salar L.)

Soybean meal-induced enteritis (SBMIE) is a well-described condition in the distal intestine of salmonids, and saponins have been implicated as the causal agent. However, the question remains whether saponins alone cause SBMIE. Moreover, the dose-response relationship has not been described. In a 10 week feeding trial with Atlantic salmon, a highly purified (95%) soya saponin preparation was supplemented (0, 2, 4, 6, or 10 g/kg) to two basal diets, one containing fishmeal as the major protein source (FM) and the other 25% lupin meal (LP). Saponins caused dose-dependent increases in the severity of inflammation independent of the basal diet, with concomitant alterations in digestive functions and immunological marker expression. Thus, saponins induced inflammation whether the diet contained other legume components or not. However, responses were often the same or stronger in fish fed the corresponding saponin-supplemented LP diets despite lower saponin exposure, suggesting potentiation by other legume component(s).

Inclusion of Palmaria palmata (red seaweed) in Atlantic salmon diets: effects on the quality, shelf-life parameters and sensory properties of fresh and cooked salmon fillets

BACKGROUND

The use of Palmaria palmata (PP) as a natural ingredient in farmed Atlantic salmon diets was investigated. The effect of salmon diet supplementation with P. palmata (0, 5, 10 and 15%) or synthetic astaxanthin (positive control, PC) for 16 weeks pre-slaughter on quality indices of fresh salmon fillets was examined. The susceptibility of salmon fillets/homogenates to oxidative stress conditions was also measured.

RESULTS

In salmon fillets stored in modified atmosphere packs (60% N2 /40% CO2 ) for up to 15 days at 4 °C, P. palmata increased surface -a* (greenness) and b* (yellowness) values in a dose-dependent manner, resulting in a final yellow/orange flesh colour. In general, the dietary addition of P. palmata had no effect on pH, lipid oxidation (fresh, cooked and fillet homogenates) and microbiological status. 'Eating quality' sensory descriptors (texture, odour and oxidation flavour) in cooked salmon fillets were not influenced by dietary P. palmata. Salmon fed 5% PP showed increased overall acceptability compared with those fed PC and 0% PP.

CONCLUSION

Dietary P. palmata was ineffective at providing red coloration in salmon fillets, but pigment deposition enhanced fillets with a yellow/orange colour. Carotenoids from P. palmata may prove to be a natural pigment alternative to canthaxanthin in salmon feeds.

Modifying effects of vitamin E on chlorpyrifos toxicity in atlantic salmon

The aim of this study was to elucidate how vitamin E (alpha tocopherol) may ameliorate the toxicity of the pesticide chlorpyrifos in Atlantic salmon. Freshly isolated hepatocytes were exposed to vitamin E, chlorpyrifos or a combination of vitamin E and chlorpyrifos (all 100 μM). Transcriptomics (RNA-seq) and metabolomics were used to screen for effects of vitamin E and chlorpyrifos. By introducing vitamin E, the number of upregulated transcripts induced by chlorpyrifos exposure was reduced from 941 to 626, while the number of downregulated transcripts was reduced from 901 to 742 compared to the control. Adding only vitamin E had no effect on the transcriptome. Jak-STAT signaling was the most significantly affected pathway by chlorpyrifos treatment according to the transcriptomics data. The metabolomics data showed that accumulation of multiple long chain fatty acids and dipeptides and amino acids in chlorpyrifos treated cells was partially alleviated by vitamin E treatment. Significant interaction effects between chlorpyrifos and vitamin E were seen for 15 metabolites, including 12 dipeptides. The antioxidant had relatively modest effects on chlorpyrifos-induced oxidative stress. By combining the two data sets, the study suggests that vitamin E supplementation prevents uptake and accumulation of fatty acids, and counteracts inhibited carbohydrate metabolism. Overall, this study shows that vitamin E only to a moderate degree modifies chlorpyrifos toxicity in Atlantic salmon liver cells.

Cloning and characterization of the proximal promoter region of rainbow trout (Oncorhynchus mykiss) interleukin-6 gene

Interleukin-6 (IL6) is a pleiotropic cytokine with important immunoregulatory functions. Its expression is inducible in immune cells and tissues of several fish species. We also found that IL6 mRNA abundance was significantly increased in spleen, liver, and gill of rainbow trout after experimental infection with Aeromonas salmonicida. Genomic DNA sequences of IL6 orthologs from three salmonid species revealed a conserved exon/intron structure and a high overall nucleotide identity of >88%. To uncover key mechanisms regulating IL6 expression in salmonid fish, we amplified a fragment of the proximal IL6 promoter from rainbow trout and identified in-silico conserved binding sites for NF-κB and CEBP. The activity of this IL6 promoter fragment was analyzed in the established human embryonic kidney line HEK-293. Luciferase- and GFP-based reporter systems revealed that the proximal IL6 promoter is activated by Escherichia coli. Essentially, both reporter systems proved that NF-κB p50, but not NF-κB p65 or CEBP, activates the IL6 promoter fragment. Truncation of this fragment caused a significant decrease in IL6 promoter activation. This characterization of the proximal promoter of the IL6-encoding gene provides basic knowledge about the IL6 gene expression in rainbow trout.

Unraveling the estrogen receptor (er) genes in Atlantic salmon (Salmo salar) reveals expression differences between the two adult life stages but little impact from polychlorinated biphenyl (PCB) load

Estrogen receptors (ers) not only are activated by hormones but also interact with many human-derived environmental contaminants. Here, we present evidence for four expressed er genes in Atlantic salmon cDNA - two more ers (erα2 and erβ2) than previously published. To determine if er gene expression differs between two adult life-stages we sampled 20 adult salmon from the feeding phase in the Baltic Sea and during migration in the River Mörrum, Sweden. Results show that all four er genes are present in the investigated tissues, except for erα2 not appearing in the spleen. Overall, a profile analysis reveals the erα1 gene to be the most highly expressed er gene in both female and male Baltic Sea salmon tissues, and also in female River Mörrum salmon. In contrast, this gene has the lowest gene expression level of the four er genes in male salmon from the River Mörrum. The erα2 gene is expressed at the lowest levels in both female/male Baltic Sea salmon and in female River Mörrum salmon. Statistical analyses indicate a significant and complex interaction where both sex and adult life stage can impact er gene expression. Regression analyses did not demonstrate any significant relationship between polychlorinated biphenyl (PCB) body burden and er gene expression level, suggesting that accumulated pollutants from the Baltic Sea may be deactivated inside the salmon's lipid tissues and have limited impact on er activity. This study is the first comprehensive analysis of four er gene expression levels in two wild salmon populations from two different adult life stages where information about PCB load is also available.

Method development for the simultaneous determination of polybrominated, polychlorinated, mixed polybrominated/chlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls and polybrominated diphenyl ethers in fish

An analytical methodology was developed for simultaneous determination of five groups of persistent organic pollutants (POPs) including polybrominated, polychlorinated and mixed brominated-chlorinated dibenzo-p-dioxins and dibenzofurans (PBDD/DFs, PCDD/DFs and PXDD/DFs, respectively), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in fish samples. The presented analytical approach was based on well established and robust method for determination of PCDD/DFs and PCBs, which was augmented with gas chromatography coupled to high resolution mass spectrometry (GC-HRMS) to include PBDEs, as well as poorly investigated PBDD/DFs and PXDD/DFs at toxicologically significant levels. Intensive clean-up and fractionation procedures in combination with optimized instrumental parameters provided reliable detection and quantification of these compounds. The application of (13)C12-labeled surrogates of analyzed compounds allowed the internal standardization and accurate measurement of selected contaminants. The developed procedure was validated while taking into account the Commission Regulation (EU) 252/2012 requirements for PCDD/DFs and PCBs, and was used to measure the occurrence of priority POPs in Baltic wild salmon.

Dose-dependent hepatic transcriptional responses in Atlantic salmon (Salmo salar) exposed to sublethal doses of gamma radiation

Due to the production of free radicals, gamma radiation may pose a hazard to living organisms. The high-dose radiation effects have been extensively studied, whereas the ecotoxicity data on low-dose gamma radiation is still limited. The present study was therefore performed using Atlantic salmon (Salmo salar) to characterize effects of low-dose (15, 70 and 280 mGy) gamma radiation after short-term (48h) exposure. Global transcriptional changes were studied using a combination of high-density oligonucleotide microarrays and quantitative real-time reverse transcription polymerase chain reaction (qPCR). Differentially expressed genes (DEGs; in this article the phrase gene expression is taken as a synonym of gene transcription, although it is acknowledged that gene expression can also be regulated, e.g., at protein stability and translational level) were determined and linked to their biological meanings predicted using both Gene Ontology (GO) and mammalian ortholog-based functional analyses. The plasma glucose level was also measured as a general stress biomarker at the organism level. Results from the microarray analysis revealed a dose-dependent pattern of global transcriptional responses, with 222, 495 and 909 DEGs regulated by 15, 70 and 280 mGy gamma radiation, respectively. Among these DEGs, only 34 were commonly regulated by all radiation doses, whereas the majority of differences were dose-specific. No GO functions were identified at low or medium doses, but repression of DEGs associated with GO functions such as DNA replication, cell cycle regulation and response to reactive oxygen species (ROS) were observed after 280mGy gamma exposure. Ortholog-based toxicity pathway analysis further showed that 15mGy radiation affected DEGs associated with cellular signaling and immune response; 70mGy radiation affected cell cycle regulation and DNA damage repair, cellular energy production; and 280mGy radiation affected pathways related to cell cycle regulation and DNA repair, mitochondrial dysfunction and immune functions. Twelve genes representative of key pathways found in this study were verified by qPCR. Potential common MoAs of low-dose gamma radiation may include induction of oxidative stress, DNA damage and disturbance of oxidative phosphorylation (OXPHOS). Although common MoAs were proposed, a number of DEGs and pathways were still found to be dose-specific, potentially indicating multiple mechanisms of action (MOAs) of low-dose gamma radiation in fish. In addition, plasma glucose displayed an apparent increase with increasing radiation doses, although the results were not significantly different from the control. These findings suggested that sublethal doses of gamma radiation may cause dose-dependent transcriptional changes in the liver of Atlantic salmon after short-term exposure. The current study predicted multiple MoA for gamma radiation and may aid future impact assessment of environmental radioactivity in fish.

Effects of TLR agonists and viral infection on cytokine and TLR expression in Atlantic salmon (Salmo salar)

The development of efficient and cheap vaccines against several aquatic viruses is necessary for a sustainable fish farming industry. Toll-like receptor (TLR) ligands have already been used as good adjuvants in human vaccines. With more understanding of TLR expression, function, and ligand specificity in fish, more efficient adjuvants for fish viral vaccines can be developed. In this paper, we examine all known TLRs in Atlantic salmon (Salmo salar) and demonstrate that head kidney and spleen are the main organs expressing TLRs in salmon. We also show that adherent head kidney leucocytes from salmon are able to respond to many of the known agonists for human TLRs, and that viral infection can induce up-regulation of several TLRs. These findings substantiate these receptors' role in immune responses to pathogens in salmonids making their ligands attractive as vaccine adjuvant candidates.

Isolation and activity of the promoters for STAT1 and 2 in Atlantic salmon Salmo salar

Signal Transducer and Activator of Transcription (STAT) 1 and 2 molecules are part of the interferon (IFN) type I and type II (γIFN) signalling pathways, key pathways in the innate immune response. Genomic sequence regions upstream from the 5-prime Salmo salar ORFs were obtained and shown to have functional activity through their incorporation into luciferase reporter constructs and subsequent activation by salmonid alpha virus (SAV). The STAT1 and STAT2 putative promoter regions were also induced by co-transfected plasmids expressing γIFN and IFN type I respectively. Two IFN-induced gene regulatory motifs (GAAANN) associated in a complete Interferon Stimulating Response Element (ISRE) were identified in the STAT1 putative promoter sequence and several GAS elements conforming to Boehm's consensus TTNCNNNAA. Sixteen IFN-induced gene regulatory motifs (GAAANN) could be identified in the STAT2 putative promoter region but no Boehm's GAS element nor ISRE. A palindromic sequence that conforms to Decker's consensus GAS element TTCNNN(N)GAA was identified. The reporter constructs generated here may prove an additional tool for refining knowledge on interferon signalling in fish and the inhibition of such by some fish viral pathogens.

The expanding repertoire of the IL-12 cytokine family in teleost fish: Identification of three paralogues each of the p35 and p40 genes in salmonids, and comparative analysis of their expression and modulation in Atlantic salmon Salmo salar

Interleukin (IL)-12 family cytokines are heterodimers of an α-chain (p19, p28 and p35) and a β-chain (p40 and Ebi3), present as IL-12 (p35/p40), IL-23 (p19/p40), IL-27 (p28/Ebi3) and IL-35 (p35/Ebi3), and play key roles in immune responses in mammals. One p35 and up to three p40 genes have been cloned in some fish species. The identification of three active p35 genes, along with three p40 paralogues in salmonids in the current study further expands the repertoire of IL-12, IL-23 and IL-35 molecules in these species. The multiple p35 genes in teleost fish appear to have arisen via whole genome duplications. The different paralogues of the subunits are divergent, and differentially expressed and modulated by PAMPs and proinflammatory cytokines, hinting that distinct isoforms could be produced in response to infection. Therefore, the expanded IL-12 cytokine family may provide an unprecedented level of regulation to fine tune the immune response in fish.

Interactions between dietary docosahexaenoic acid and other long-chain polyunsaturated fatty acids on performance and fatty acid retention in post-smolt Atlantic salmon (Salmo salar)

A study with varying dietary inclusion levels (1, 5, 10, 15 and 20 g kg(-1)) of docosahexaenoic acid (DHA; 22:6n-3) was conducted with post-smolt (111 ± 2.6 g; mean ± S.) Atlantic salmon (Salmo salar) over a 9-week period. In addition to the series of DHA inclusion levels, the study included further diets that had DHA at 10 g kg(-1) in combination with either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), both also included at 10 g kg(-1). An additional treatment with both EPA and DHA included at 5 g kg(-1) (total of 10 g kg(-1) long-chain polyunsaturated fatty acids, LC-PUFA) was also included. After a 9-week feeding period, fish were weighed, and carcass, blood and tissue samples collected. A minor improvement in growth was seen with increasing inclusion of DHA. However, the addition of EPA further improved growth response while addition of ARA had no effect on growth. As with most lipid studies, the fatty acid composition of the whole body lipids generally reflected that of the diets. However, there were notable exceptions to this, and these implicate some interactions among the different LC-PUFA in terms of the fatty acid biochemistry in this species. At very low inclusion levels, DHA retention was substantially higher (~250%) than that at all other inclusion levels (31-58%). The inclusion of EPA in the diet also had a positive effect on the retention efficiency of DHA. However, EPA retention was highly variable and at low DHA inclusion levels there was a net loss of EPA as this fatty acid was most likely elongated to produce DHA, consistent with increased DHA retention with additional EPA in the diet. Retention of DPA (22:5n-3) was high at low levels of DHA, but diminished with increasing DHA inclusion, similar to that seen with DHA retention. The addition of EPA to the diet resulted in a substantial increase in the efficiency of DPA retention; the inclusion of ARA had the opposite effect. Retention of ARA was unaffected by DHA inclusion, but the addition of either EPA or ARA to the diet resulted in a substantial reduction in the efficiency of ARA retention. No effects of dietary treatment were noted on the retention of either linolenic (18:3n-3) or linoleic (18:2n-6) acids. When the total n-3 LC-PUFA content of the diet was the same but consisted of either DHA alone or as a combination of EPA plus DHA, the performance effects were similar.

Regulation of the seasonal leptin and leptin receptor expression profile during early sexual maturation and feed restriction in male Atlantic salmon, Salmo salar L., parr

In mammals, leptin acts as an adiposity signal and is a crucial link between nutritional status and the reproductive axis. So far the link between leptin and energy balance during sexual maturation in teleosts has been poorly investigated. In this study, seasonal gene expression changes in two leptin genes (lepa1 and lepa2) and the leptin receptor were investigated during early sexual maturation in male Atlantic salmon parr under fully fed (control) and feed restricted conditions from April through September. Both Atlantic salmon lepa1 and lepa2 in the liver and lepr in the brain were significantly down-regulated in non-maturing control males in early spring, coinciding with the start of the growth and fat accumulation. In maturing control males, hepatic leptin expression increased during mid-spermatogenesis and lepa1 and lepa2 mRNA levels were up-regulated by 7.7 and 49 times respectively during final maturation. For the first time in a fish species, a significant up-regulation of lepr expression was observed in the testis throughout mid to late spermatogenesis. Feed restriction decreased the incidence of sexual maturation by 53% and highly up-regulated both leptin genes in the liver and the leptin receptor in the pituitary. This study shows that hepatic lepa1 and lepa2 expression and lepr expression in the testis is affected by early sexual maturation in male Atlantic salmon parr. Fast growth and high fat stores are associated with low leptin levels while feed restriction has a stimulatory effect on hepatic leptin and leptin receptor gene expression in the pituitary, suggesting a role for leptin other than that as an adiposity signal.

Cloning and characterisation of multiple ferritin isoforms in the Atlantic salmon (Salmo salar)

Ferritin is a highly-conserved iron-storage protein that has also been identified as an acute phase protein within the innate immune system. The iron-storage function is mediated through complementary roles played by heavy (H)-chain subunit as well as the light (L) in mammals or middle (M)-chain in teleosts, respectively. In this study, we report the identification of five ferritin subunits (H1, H2, M1, M2, M3) in the Atlantic salmon that were supported by the presence of iron-regulatory regions, gene structure, conserved domains and phylogenetic analysis. Tissue distribution analysis across eight different tissues showed that each of these isoforms is differentially expressed. We also examined the expression of the ferritin isoforms in the liver and kidney of juvenile Atlantic salmon that was challenged with Aeromonas salmonicida as well as in muscle cell culture stimulated with interleukin-1β. We found that each isoform displayed unique expression profiles, and in certain conditions the expressions between the isoforms were completely diametrical to each other. Our study is the first report of multiple ferritin isoforms from both the H- and M-chains in a vertebrate species, as well as ferritin isoforms that showed decreased expression in response to infection. Taken together, the results of our study suggest the possibility of functional differences between the H- and M-chain isoforms in terms of tissue localisation, transcriptional response to bacterial exposure and stimulation by specific immune factors.

Influence of dietary docosahexaenoic acid in combination with other long-chain polyunsaturated fatty acids on expression of biosynthesis genes and phospholipid fatty acid compositions in tissues of post-smolt Atlantic salmon (Salmo salar)

To investigate interactions of dietary LC-PUFA, a dose-response study with a range of docosahexaenoic acid (DHA; 22:6n-3) levels (1 g kg(-1), 5 g kg(-1), 10 g kg(-1), 15 g kg(-1) and 20 g kg(-1)) was performed with post-smolts (111 ± 2.6g; mean ± S.D.) over a nine-week feeding period. Additional diets included 10 g kg(-1) DHA in combination with 10 g kg(-1) of either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), and a diet containing 5 g kg(-1) each of DHA and EPA. The liver, brain, head kidney and gill were collected at the conclusion of the trial, and lipid and fatty acid compositions were determined as well as expression of genes of LC-PUFA biosynthesis. Total lipid content and class composition were largely unaffected by changes in dietary LC-PUFA. However, phospholipid (PL) fatty acid compositions generally reflected that of the diet, although the response varied between tissues. The liver most strongly reflected diet, followed by the head kidney. In both tissues increasing dietary DHA led to significantly increased DHA in PL and inclusion of EPA or ARA led to higher levels of these fatty acids. The brain showed the most conserved composition and gene expression profile, with increased dietary LC-PUFA resulting in only minor changes in PL fatty acids. Dietary LC-PUFA significantly affected the expression of Δ6 and Δ5 desaturases, Elovl 2, 4 and 5, and SREBPs although this varied between tissues with greatest effects observed in the liver followed by the head kidney, similar to PL fatty acid compositions.

Delayed phenotypic expression of growth hormone transgenesis during early ontogeny in Atlantic salmon (Salmo salar)?

Should growth hormone (GH) transgenic Atlantic salmon escape, there may be the potential for ecological and genetic impacts on wild populations. This study compared the developmental rate and respiratory metabolism of GH transgenic and non-transgenic full sibling Atlantic salmon during early ontogeny; a life history period of intense selection that may provide critical insight into the fitness consequences of escaped transgenics. Transgenesis did not affect the routine oxygen consumption of eyed embryos, newly hatched larvae or first-feeding juveniles. Moreover, the timing of early life history events was similar, with transgenic fish hatching less than one day earlier, on average, than their non-transgenic siblings. As the start of exogenous feeding neared, however, transgenic fish were somewhat developmentally behind, having more unused yolk and being slightly smaller than their non-transgenic siblings. Although such differences were found between transgenic and non-transgenic siblings, family differences were more important in explaining phenotypic variation. These findings suggest that biologically significant differences in fitness-related traits between GH transgenic and non-transgenic Atlantic salmon were less than family differences during the earliest life stages. The implications of these results are discussed in light of the ecological risk assessment of genetically modified animals.

A co culture approach show that polyamine turnover is affected during inflammation in Atlantic salmon immune and liver cells and that arginine and LPS exerts opposite effects on p38MAPK signaling

This study assess which pathways and molecular processes are affected by exposing salmon head kidney cells or liver cells to arginine supplementation above the established requirements for growth support. In addition to the conventional mono cultures of liver and head kidney cells, co cultures of the two cell types were included in the experimental set up. Responses due to elevated levels of arginine were measured during inflammatory (lipopolysaccharide/LPS) and non -inflammatory conditions. LPS up regulated the genes involved in polyamine turnover; ODC (ornithine decarboxylase), SSAT (spermidine/spermine-N1-acetyltransferase) and SAMdc (S-adenosyl methionine decarboxylase) in head kidney cells when co cultured with liver cells. Regardless of treatment, liver cells in co culture up regulated ODC and down regulated SSAT when compared to liver mono cultures. This suggests that polyamines have anti-inflammatory properties and that both salmon liver cells and immune cells seem to be involved in this process. The transcription of C/EBP β/CCAAT, increased during inflammation in all cultures except for liver mono cultures. The observed up regulation of this gene may be linked to glucose transport due to the highly variable glucose concentrations found in the cell media. PPARα transcription was also increased in liver cells when receiving signals from head kidney cells. Gene transcription of Interleukin 1β (IL-1β), Interleukin-8 (IL-8), cyclooxygenase 2 (COX2) and CD83 were elevated during LPS treatment in all the head kidney cell cultures while arginine supplementation reduced IL-1β and IL-8 transcription in liver cells co cultured with head kidney cells. This is probably connected to p38MAPK signaling as arginine seem to affect p38MAPK signaling contrary to the LPS induced p38MAPK signaling, suggesting anti-inflammatory effects of arginine/arginine metabolites. This paper shows that co culturing these two cell types reveals the connection between metabolism and inflammation, suggesting different pathways and candidate biomarkers to be further explored.

Accumulation of heavy metals in different body tissues of Atlantic salmon, Salmo salar L., exposed to a model mixture (Cu, Zn, Ni, Cr, Pb, Cd) and singly to nickel, chromium, and lead

One-year-old Atlantic salmon smolts were exposed for 2 weeks either to six priority heavy metal mixture or to Ni, Pb, and Cr singly at a concentration corresponding to Lithuanian inland water standards: Cu - 0.01, Zn - 0.1, Ni - 0.01, Cr - 0.01, Cd - 0.005 and Pb - 0.005 mg/L, respectively under semi-static conditions. The presence of metal mixture in the water only partly (by 50 %) affected the accumulation of single metals in body tissues (muscle, gills, liver and kidneys) probably due to the synergistic interactions among metals. Although metal concentrations increased in most cases, only Pb exceeded recommended level for human consumption (0.2 Pb mg/L) by 1.1-fold to 2.1-fold.

Salinity and photoperiod modulate pubertal development in Atlantic salmon (Salmo salar)

The Atlantic salmon shows substantial life cycle plasticity, which also applies to the timing of puberty. While it is characterized by the activation of the brain-pituitary-gonad axis, many morphophysiological aspects of puberty and the influence of environmental conditions, such as water salinity, are not well understood in fish. Here, 12-month-old Atlantic salmon coming from an out-of-season smoltification regime in December were exposed to freshwater (FW) or seawater (SW) at 16 °C to stimulate puberty under a 24-h constant light (LL) or 12 h light:12 h darkness (LD) photoperiod. These four treatment groups (FWLL, SWLL, FWLD, and SWLD) were studied from January to March. Next to 11-ketotestosterone (11-KT) plasma levels, the expression of pituitary genes (gnrhr4, fshb, and lhb) and spermatogenesis was quantified. When spermatogonial proliferation started, fshb mRNA levels increased steeply and began to decrease when spermatogonial mitosis approached completion and most germ cells had reached meiotic or post-meiotic stages. Conversely, lhb mRNA levels increased progressively during spermatogenesis. Most males in all treatment groups matured, but exposure to SW resulted in the strongest stimulation of the onset of spermatogenesis and elevation of pituitary gnrhr4 and fshb mRNA levels. Later on, the LD photoperiod accelerated, irrespective of the salinity, the completion of spermatogenesis, associated with higher lhb mRNA and 11-KT plasma levels than in the LL groups. We find that both salinity and photoperiod modulated different aspects of spermatogenesis, and resulted in a differential activation of pituitary and testis functions; SW stimulating the onset and the shorter photoperiod the completion of spermatogenesis.

Effects of dietary plant meal and soya-saponin supplementation on intestinal and hepatic lipid droplet accumulation and lipoprotein and sterol metabolism in Atlantic salmon (Salmo salar L.)

Altered lipid metabolism has been shown in fish fed plant protein sources. The present study aimed to gain further insights into how intestinal and hepatic lipid absorption and metabolism are modulated by plant meal (PM) and soya-saponin (SA) inclusion in salmon feed. Post-smolt Atlantic salmon were fed for 10 weeks one of four diets based on fishmeal or PM, with or without 10 g/kg SA. PM inclusion resulted in decreased growth performance, excessive lipid droplet accumulation in the pyloric caeca and liver, and reduced plasma cholesterol levels. Intestinal and hepatic gene expression profiling revealed an up-regulation of the expression of genes involved in lipid absorption and lipoprotein (LP) synthesis (apo, fatty acid transporters, microsomal TAG transfer protein, acyl-CoA cholesterol acyltransferase, choline kinase and choline-phosphate cytidylyltransferase A), cholesterol synthesis (3-hydroxy-3-methylglutaryl-CoA reductase) and associated transcription factors (sterol regulatory element-binding protein 2 and PPARγ). SA inclusion resulted in reduced body pools of cholesterol and bile salts. The hepatic gene expression of the rate-limiting enzyme in bile acid biosynthesis (cytochrome P450 7A1 (cyp7a1)) as well as the transcription factor liver X receptor and the bile acid transporter abcb11 (ATP-binding cassette B11) was down-regulated by SA inclusion. A significant interaction was observed between PM inclusion and SA inclusion for plasma cholesterol levels. In conclusion, gene expression profiling suggested that the capacity for LP assembly and cholesterol synthesis was up-regulated by PM exposure, probably as a compensatory mechanism for excessive lipid droplet accumulation and reduced plasma cholesterol levels. SA inclusion had hypocholesterolaemic effects on Atlantic salmon, accompanied by decreased bile salt metabolism.

Stable isotope analyses on archived fish scales reveal the long-term effect of nitrogen loads on carbon cycling in rivers

Stable isotope analysis of organic matter in sediment records has long been used to track historical changes in productivity and carbon cycling in marine and lacustrine ecosystems. While flow dynamics preclude stratigraphic measurements of riverine sediments, such retrospective analysis is important for understanding biogeochemical cycling in running waters. Unique collections of riverine fish scales were used to analyse δ(15) N and δ(13) C variations in the food web of two European rivers that experience different degrees of anthropogenic pressure. Over the past four decades, dissolved inorganic N loading remained low and constant in the Teno River (70°N, Finland); in contrast, N loading increased fourfold in the Scorff River (47°N, France) over the same period. Archived scales of Atlantic salmon parr, a riverine life-stage that feeds on aquatic invertebrates, revealed high δ(15) N values in the Scorff River reflecting anthropogenic N inputs to that riverine environment. A strong correlation between dissolved inorganic N loads and δ(13) C values in fish scales was observed in the Scorff River, whereas no trend was found in the Teno River. This result suggests that anthropogenic N-nutrients enhanced atmospheric C uptake by primary producers and its transfer to fish. Our results illustrate for the first time that, as for lakes and marine ecosystems, historical changes in anthropogenic N loading can affect C cycling in riverine food webs, and confirm the long-term interactions between N and C biogeochemical cycles in running waters.

Coping with unpredictability: dopaminergic and neurotrophic responses to omission of expected reward in Atlantic salmon (Salmo salar L.)

Comparative studies are imperative for understanding the evolution of adaptive neurobiological processes such as neural plasticity, cognition, and emotion. Previously we have reported that prolonged omission of expected rewards (OER, or 'frustrative nonreward') causes increased aggression in Atlantic salmon (Salmo salar). Here we report changes in brain monoaminergic activity and relative abundance of brain derived neurotrophic factor (BDNF) and dopamine receptor mRNA transcripts in the same paradigm. Groups of fish were initially conditioned to associate a flashing light with feeding. Subsequently, the expected food reward was delayed for 30 minutes during two out of three meals per day in the OER treatment, while the previously established routine was maintained in control groups. After 8 days there was no effect of OER on baseline brain stem serotonin (5-HT) or dopamine (DA) activity. Subsequent exposure to acute confinement stress led to increased plasma cortisol and elevated turnover of brain stem DA and 5-HT in all animals. The DA response was potentiated and DA receptor 1 (D1) mRNA abundance was reduced in the OER-exposed fish, indicating a sensitization of the DA system. In addition OER suppressed abundance of BDNF in the telencephalon of non-stressed fish. Regardless of OER treatment, a strong positive correlation between BDNF and D1 mRNA abundance was seen in non-stressed fish. This correlation was disrupted by acute stress, and replaced by a negative correlation between BDNF abundance and plasma cortisol concentration. These observations indicate a conserved link between DA, neurotrophin regulation, and corticosteroid-signaling pathways. The results also emphasize how fish models can be important tools in the study of neural plasticity and responsiveness to environmental unpredictability.

Organohalogen concentrations and feeding status in Atlantic salmon (Salmo salar L.) of the Baltic Sea during the spawning run

Changes in the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in Baltic salmon muscle were studied during the spawning migration from the southern Baltic Sea to rivers flowing into the northern Gulf of Bothnia and during the spawning period. The aim was to obtain information to facilitate the arrangement of salmon fisheries such that the human dioxin intake is taken into account. The EC maximum allowable total toxic equivalent concentration (WHO-TEQPCDD/F+PCB) was exceeded in the muscle of the majority of the migrating salmon, except in the Baltic Proper. The fresh-weight-based concentrations of all toxicant groups in salmon tended to be the lowest in the Baltic Proper and the Northern Quark, and all toxicant concentrations, except PCDDs and PCDFs, were significantly higher in the spawning salmon than in the salmon caught during the spawning run. The fat content of the salmon muscle decreased by 60% during the spawning run, and the lipid-based total toxicant concentrations were consequently 4.2-6.2 times higher during the spawning period than during the spawning migration. However, the toxicants were concentrated just before spawning, and thus there is no essential difference related to whether the salmon are caught in the sea or the recreational river fishery.

Toxicity and accumulation of trinitrotoluene (TNT) and its metabolites in Atlantic salmon alevins exposed to an industrially polluted water

A pond in an industrial area in Sweden was selected to study adverse effects on salmon alevins from 2,4,6-trinitrotoluene (TNT)-contaminated water. Chemical screening revealed heavy contamination of TNT and its degradation products, 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT), ranging from 0.05 to 230 g/kg in the sediment (dry weight) within the water system. Pond water contained 3 mg/L TNT. A dilution series of pond water mixed with tap water revealed increased death frequency in alevins down to fivefold dilution (approximate 0.4 mg TNT/L). Uptake was concentration dependent, reaching 7, 9, and 22 μg/g tissue for TNT, 2-ADNT, and 4-ADNT at the highest test concentration. A time-dependent uptake of TNT and its degradation products was found at a water concentration of 0.08 mg TNT/L. Degradation products of TNT showed a more efficient uptake compared to native TNT, and accumulation of 4-ADNT was more pronounced during the late phase of the 40-d exposure study. Bioconcentration factors (BCF) (0.34, 52, and 134 ml/g for TNT, 2-ADNT, and 4-ADNT, respectively) demonstrated a significant uptake of the metabolite 4-ADNT in alevin tissue. Disturbed physiological conditions and delayed development in alevins were not studied, but may not be excluded even at 125-fold diluted pond water (0.016 mg TNT/L). BCF data indicated that bioaccumulation of TNT metabolites need to be considered in TNT chronic toxicity. Fish species and age differences in the accumulation of TNT metabolites need to be further studied.

The Atlantic salmon protein tyrosine kinase Tyk2: molecular cloning, modulation of expression and function

Tyk2, a member of the Janus Kinase (JAK) family of protein tyrosine kinases, is required for interferon-α/β binding and signaling in higher vertebrates. Currently, little is known about the role of the different JAKs in signaling responses to interferon (IFN) in lower vertebrates including fish. In this paper we report the identification and characterization of Atlantic salmon (Salmo salar) Tyk2. Four cDNA sequences, two containing an open reading frame encoding full-length Tyk protein and two with an up-stream in frame stop codon, were identified. The deduced amino acid sequences of the salmon full-length Tyk2 proteins showed highest identity with Tyk2 from other species and their transcripts were ubiquitously expressed. Like in mammals the presented data suggests that salmon Tyk2 is auto-phosporylated when ectopically expressed in cells. In our experiments, full-length salmon Tyk2 overexpressed in CHSE-cells phosphorylated itself, while both a kinase-deficient mutant and the truncated Tyk2 (Tyk-short) were inactive. Interestingly, the overexpression of full length Tyk2 was shown to up-regulate the transcript levels of the IFN induced gene Mx, thus indicating the involvement of salmon Tyk2 in the salmon IFN I pathway.

Dietary synbiotic application modulates Atlantic salmon (Salmo salar) intestinal microbial communities and intestinal immunity

A feeding trial was conducted to determine the effect of dietary administration of Pediococcus acidilactici MA18/5M and short chain fructooligosaccharides (scFOS) on Atlantic salmon (Salmo salar L.) intestinal health. Salmon (initial average weight 250 g) were allocated into triplicate sea pens and were fed either a control diet (commercial diet: 45% protein, 20% lipid) or a synbiotic treatment diet (control diet + P. acidilactici at 3.5 g kg(-1) and 7 g kg(-1) scFOS) for 63 days. At the end of this period, fish were sampled for intestinal microbiology, intestinal histology and the expression of selected immune-related genes (IL1β, TNFα, IL8, TLR3 and MX-1) in the intestine. Compared to the control fish, the total bacterial levels were significantly lower in the anterior mucosa, posterior mucosa and posterior digesta of the synbiotic fed fish. qPCR revealed good recovery (log 6 bacteria g(-1)) of the probiotic in the intestinal digesta of the synbiotic fed fish and PCR-DGGE revealed that the number of OTUs, as well as the microbial community diversity and richness were significantly higher in the anterior digesta of the synbiotic fed fish than the control. Compared to the control fed fish, the mucosal fold (villi) length and the infiltration of epithelial leucocytes were significantly higher in the anterior and posterior intestine, respectively, in the synbiotic group. Real-time PCR demonstrated that all of the genes investigated were significantly up-regulated in the anterior and posterior intestine of the synbiotic fed salmon, compared to the control group. At the systemic level, serum lysozyme activity was significantly higher in the synbiotic fed fish and growth performance, feed utilisation and biometric measurements (condition factor, gutted weight and gut loss) were not affected. Together these results suggest that the synbiotic modulation of the gut microbiota has a protective action on the intestinal mucosal cells, improving morphology and stimulating the innate immune response without negatively affecting growth performance or feed utilization of farmed Atlantic salmon.