Gills Of Salmon Research Articles

Genotyping of Candidatus Syngnamydia salmonis (chlamydiales; Simkaniaceae) co-cultured in Paramoeba perurans (amoebozoa; Paramoebidae)

Candidatus Syngnamydia salmonis (Chlamydiales, Simkaniaceae) was described as an epitheliocystis-causing bacterium from the gills of Atlantic salmon (Salmo salar) in Norway. A bacterium showing 99.2% 16S rRNA identity to Cand. S. salmonis is able to multiply in Paramoeba perurans and based on the classification criteria this bacterium could represent the same species as Cand. S. salmonis. Sequencing the genome of the cultured bacterium has made it possible to fulfill the minimal standards for genetic characterization of species within the order Chlamydiales. The complete rRNA genes, the amino acid sequences of SucA, PepF, Adk, HemL, DnaA, FtsK and FabI, are presented in addition to the morphology of the Chlamydia-like morphs in the cytoplasm of P. perurans.

Development and characterization of two cell lines from gills of Atlantic salmon.

Gill disease in Atlantic salmon, Salmo salar L., causes big losses in the salmon farming industry. Until now, tools to cultivate microorganisms causing gill disease and models to study the gill responses have been lacking. Here we describe the establishment and characterization of two cell lines from the gills of Atlantic salmon. Atlantic salmon gill cell ASG-10 consisted of cells staining for cytokeratin and e-cadherin and with desmosomes as seen by transmission electron microscopy suggesting the cells to be of epithelial origin. These structures were not seen in ASG-13. The cell lines have been maintained for almost 30 passages and both cell lines are fully susceptible to infection by infectious hematopoietic necrosis virus (IHNV), viral hemorrhagic septicemia virus (VHSV), infectious pancreatic necrosis virus (IPNV), Atlantic salmon reovirus TS (TSRV) and Pacific salmon paramyxovirus (PSPV). While infectious salmon anemia virus (ISAV) did not cause visible CPE, immunofluorescent staining revealed a sub-fraction of cells in both the ASG-10 and ASG-13 lines may be permissive to infection. ASG-10 is able to proliferate and migrate to close scratches in the monolayer within seven days in vitro contrary to ASG-13, which does not appear to do have the same proliferative and migratory ability. These cell lines will be useful in studies of gill diseases in Atlantic salmon and may represent an important contribution for alternatives to experimental animals and studies of epithelial–mesenchymal cell biology.

A survey of salmon gill poxvirus (SGPV) in wild salmonids in Norway

In 2016, the Norwegian health monitoring programme for wild salmonids conducted a real-time PCR-based screening for salmon gill poxvirus (SGPV) in anadromous Arctic char (Salvelinus alpinus L.), anadromous and non-anadromous Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.). SGPV was widely distributed in wild Atlantic salmon returning from marine migration. In addition, characteristic gill lesions, including apoptosis, were detected in this species. A low amount of SGPV DNA, as indicated by high Ct-values, was detected in anadromous trout, but only in fish cohabiting with SGPV-positive salmon. SGPV was not detected in trout and salmon from non-anadromous water courses, and thus seems to be primarily linked to the marine environment. This could indicate that trout are not a natural host for the virus. SGPV was not detected in Arctic char but, due to a low sample size, these results are inconclusive. The use of freshwater from anadromous water sources may constitute a risk of introducing SGPV to aquaculture facilities. Moreover, SGPV-infected Atlantic salmon farms will hold considerable potential for virus propagation and spillback to wild populations. This interaction should therefore be further investigated.

The interbranchial lymphoid tissue likely contributes to immune tolerance and defense in the gills of Atlantic salmon

Central and peripheral immune tolerance is together with defense mechanisms a hallmark of all lymphoid tissues. In fish, such tolerance is especially important in the gills, where the intimate contact between gill tissue and the aqueous environment would otherwise lead to continual immune stimulation by innocuous antigens. In this paper, we focus on the expression of genes associated with immune regulation by the interbranchial lymphoid tissue (ILT) in an attempt to understand its role in maintaining immune homeostasis. Both healthy and virus-challenged fish were investigated, and transcript levels were examined from laser-dissected ILT, gills, head kidney and intestine. Lack of Aire expression in the ILT excluded its involvement in central tolerance and any possibility of its being an analogue to the thymus. On the other hand, the ILT appears to participate in peripheral immune tolerance due to its relatively high expression of forkhead box protein 3 (Foxp3) and other genes associated with regulatory T cells (Tregs) and immune suppression.

Primary Isolation and Characterization of Tenacibaculum maritimum from Chilean Atlantic Salmon Mortalities Associated with a Pseudochattonella spp. Algal Bloom.

This study presents the first isolation of Tenacibaculum maritimum from farmed Atlantic Salmon Salmo salar in Chile. The isolate, designated T. maritimum Ch-2402, was isolated from gills of Atlantic Salmon at a farm located in region X, Los Lagos, Chile, during the harmful algal bloom caused by Pseudochattonella spp. in February 2016. The algal bloom is reported to have caused 40,000 metric tons of mortality in this salmon farming area. The bacterium T. maritimum, which causes tenacibaculosis, is recognized as an important pathogen of marine fish worldwide. Genetic, phylogenetic, and phenotypic characterizations were used to describe the T. maritimum Ch-2402 isolate. The isolate was similar to the type strain of T. maritimum but was genetically unique. Tenacibaculum dicentrarchi isolates were also recovered during sampling from the same farm. Based on the fact that T. maritimum has been shown to cause disease in Atlantic Salmon in other regions, the presence of this bacterium poses a potential risk of disease to fish in the Chilean aquaculture industry. Received November 6, 2016; accepted May 29, 2017.

Ca. Branchiomonas cysticola, Ca. Piscichlamydia salmonis and Salmon Gill Pox Virus transmit horizontally in Atlantic salmon held in fresh water.

Elucidation of the role of infectious agents putatively involved in gill disease is commonly hampered by the lack of culture systems for these organisms. In this study, a farmed population of Atlantic salmon pre-smolts, displaying proliferative gill disease with associated Candidatus Branchiomonas cysticola, Ca.Piscichlamydia salmonis and Atlantic salmon gill pox virus (SGPV) infections, was identified. A subpopulation of the diseased fish was used as a source of waterborne infection towards a population of naïve Atlantic salmon pre-smolts. Ca.B.cysticola infection became established in exposed naïve fish at high prevalence within the first month of exposure and the bacterial load increased over the study period. Ca.P.salmonis and SGPV infections were identified only at low prevalence in exposed fish during the trial. Although clinically healthy, at termination of the trial the exposed, naïve fish displayed histologically visible pathological changes typified by epithelial hyperplasia and subepithelial inflammation with associated bacterial inclusions, confirmed by fluorescent insitu hybridization to contain Ca.B.cysticola. The results strongly suggest that Ca.B.cysticola infections transmit directly from fish to fish and that the bacterium is directly associated with the pathological changes observed in the exposed, previously naïve fish.

Salmon gill poxvirus, a recently characterized infectious agent of multifactorial gill disease in freshwater- and seawater-reared Atlantic salmon.

Gill diseases cause considerable losses in Norwegian salmon farming. In 2015, we characterized salmon gill poxvirus (SGPV) and associated gill disease. Using newly developed diagnostic tools, we show here that SGPV infection is more widely distributed than previously assumed. We present seven cases of complex gill disease in Atlantic salmon farmed in seawater and freshwater from different parts of Norway. Apoptosis, the hallmark of acute SGPV infection, was not easily observed in these cases, and qPCR analysis was critical for identification of the presence of SGPV. Several other agents including Costia-like parasites, gill amoebas, Saprolegnia spp. and bacteria were observed. The studied populations experienced significant mortalities, which increased to extreme levels when severe SGPV infections coincided with smoltification. SGPV infection appears to affect the smoltification process directly by affecting the gills and chloride cells in particular. SGPV may be considered a primary pathogen as it was often found prior to identification of complex gill disease. It is hypothesized that SGPV-induced gill damage may impair innate immunity and allow invasion of secondary invaders. The distinct possibility that SGPV has been widely overlooked as a primary pathogen calls for extended use of SGPV qPCR in Atlantic salmon gill health management.

Variation in branchial expression among insulin-like growth-factor binding proteins (igfbps) during Atlantic salmon smoltification and seawater exposure

BackgroundIn preparation for migration from freshwater to marine habitats, Atlantic salmon (Salmo salar L.) undergo smoltification, a transformation that includes the acquisition of hyposmoregulatory capacity. The growth hormone (Gh)/insulin-like growth-factor (Igf) axis promotes the development of branchial ionoregulatory functions that underlie ion secretion. Igfs interact with a suite of Igf binding proteins (Igfbps) that modulate hormone activity. In Atlantic salmon smolts, igfbp4,−5a,−5b1,−5b2,−6b1 and−6b2 transcripts are highly expressed in gill. We measured mRNA levels of branchial and hepatic igfbps during smoltification (March, April, and May), desmoltification (July) and following seawater (SW) exposure in March and May. We also characterized parallel changes in a broad suite of osmoregulatory (branchial Na+/K+-ATPase (Nka) activity, Na+/K+/2Cl−cotransporter 1 (nkcc1) and cystic fibrosis transmembrane regulator 1 (cftr1) transcription) and endocrine (plasma Gh and Igf1) parameters.ResultsIndicative of smoltification, we observed increased branchial Nka activity, nkcc1 and cftr1 transcription in May. Branchial igfbp6b1 and -6b2 expression increased coincidentally with smoltification. Following a SW challenge in March, igfbp6b1 showed increased expression while igfbp6b2 exhibited diminished expression. igfbp5a,−5b1 and−5b2 mRNA levels did not change during smolting, but each had lower levels following a SW exposure in March.ConclusionsSalmonids express an especially large suite of igfbps. Our data suggest that dynamic expression of particular igfbps accompanies smoltification and SW challenges; thus, transcriptional control of igfbps may provide a mechanism for the local modulation of Igf activity in salmon gill.

Comparative characteristics of the lipid status of gills of juvenile Atlantic salmon infected with glochidia of the freshwater pearl mussel living in rivers of the European North

A comparative study of the lipid status of gills of juvenile Atlantic salmon infested with glochidia of the freshwater pearl mussel inhabiting the Vuokinyoki (White Sea basin) and Syuskyuyanyoki (basin of Lake Ladoga) rivers in the fall is carried out. The most infested gills of juvenile salmon and the lower water temperature (1.3°C) in the Vuokinyoki River reveal higher cholesterol levels and cholesterol/phospholipids ratios, which are due to the influence of infection factors; thereby they slow down biochemical processes. It is noted that variations in the lipid composition in juvenile salmon the gills of which are infected with glochidia reflect the development of adaptive responses that maintain homeostasis of juveniles under invasion.

Immune gene expression in the gills of Atlantic salmon (Salmo salar L.) following experimental reinfection with Neoparamoeba perurans

Amoebic gill disease (AGD) is caused by Neoparamoeba perurans and represents a significant threat to Atlantic salmon marine farming in several countries worldwide. Sequential natural reinfection with N. perurans after treatment occurs after the first AGD outbreak during the grow-out phase of Atlantic salmon culture. Little is known about the immune response of Atlantic salmon following reinfection with N. perurans. In a previous single exposure study, using gill biopsies with various severity of AGD-lesion, we reported that the immune signalling in AGD-affected gills was highly dependent on the ratio of normal to hyperplastic gill tissues. Here, following experimental reinfection we investigated the transcriptional immune response in the gills of AGD-affected Atlantic salmon. Furthermore, we reported the inflammatory and immune response following a single exposure to N. perurans during late infection and compared it to the reinfected fish. Fish groups were selected based on the gross gill scores carried out during the trial. Two gill biopsies were collected from each AGD-affected individual, one with no lesion and one partly including AGD-lesion. Furthermore, gill biopsies were collected from uninfected controls. Pro-inflammatory and immune-related genes were characterised at the mRNA level by using a quantitative RT-PCR. Targeted immune genes included IL-1β, TCR-α chain, CD8, CD4, MHC-IIα, MHC-I, IgM and IgT. Histopathology and image analysis were used to assess the severity and to verify the reliability of the gross gill score as AGD severity assessment method to select fish groups for gene expression studies. Overall the expression at the mRNA level of the immune and pro-inflammatory genes analysed showed little change in AGD-affected gills of experimentally reinfected fish and of fish exposed once to N. perurans. Statement of relevanceThis research further our understanding of the mechanisms underlying AGD in Atlantic salmon and provides the bases to the potential development of immunoprophylactic treatments or other practical solutions.

Disaccharide analysis of chondroitin and heparin from farmed Atlantic salmon.

The heparin disaccharides detected in farmed Atlantic salmon (Salmo salar) gills and intestines have, with one exception, been reported in porcine heparin. The relative amounts of disaccharides appear to be very different in the two species. Two chondroitin disaccharides with a proposed essential role in the zebrafish (Danio rerio) development and differentiation are detected in farmed Atlantic salmon. In addition, most of the chondroitin/dermatan sulfate and heparin disaccharides detected here have been reported in zebrafish, in support of the claims of the heparin presence in fish. The same chondroitin/dermatan disaccharides were detected in the bones of bony fishes. The rare disaccharide UA2S-GalNAc that was found in trace amounts in all 5 bony fishes was found in relative high amounts in gills and in significant amounts in intestines. The rare heparin disaccharide UA2S-GlcN was in relative highest amounts both in gills and intestines. In context with our previous reports, this communication suggests that glycosaminoglycans in farmed Atlantic salmon heparin need further studies in order to clarify structure and function.

Smoltification and breeding for rapid growth may suppress immunity of atlantic salmon: Evidence from transcriptome analyses

The first months after seawater transfer (SWT) of fish are a period of heavy losses in commercial farming of Atlantic salmon. A large part of the mortality is due to infectious diseases, but unsuccessful smoltification and various undetected pathogens may contribute to cases that remain unexplained. SWT is preceded with smoltification, which is associated with dramatic endocrine and metabolic changes. Farmed Atlantic salmon has spent many generations under intense selective breeding for rapid growth and other commercially important traits. Given the high energy costs of smoltification and growth one may anticipate a trade off between these processes and immunity. We report studies that used gene expression profiling with oligonucleotide microarrays and RNA-seq. (1) Smoltification was induced with photoperiod manipulation, and microarray analyses were performed in samples from the head kidney, gill and intestine. Massive down-regulation of immune genes was revealed, starting from the middle of stimulation and remained constant to the end of experiment – three weeks after SWT. The innate antiviral immunity showed greatest suppression. The only deviation from the common trend was a transient increase of Ig transcripts in the gill shortly after SWT. (2) RNA-seq analyses in hearts of farmed parr and smolts produced similar results: all functional groups of immunity were down-regulated while expression of Ig increased. All immune genes in hearts of wild salmon showed higher expression in comparison with farmed fish. (3) Parr and smolts from the same batch reared respectively in fresh and seawater were challenged with PRV, the causative agent of HSMI. Microarray analyses found a minor difference between the uninfected fish. Further, parr developed more rapid responses to the pathogen, as observed by earlier induction of innate antiviral and B cells responses in the head kidney and to a lesser extent in the spleen. Clearance of PRV from spleen was more effective in parr. (4) Microarray analyses found slight but significant up-regulation in several groups of immune genes in the gill of wild anadromous salmon during smoltification, which was in contrast to farmed salmon. In conclusion, results obtained in several independent experiments, including different research stations, wild and commercial fish of different origin, provided indications for compromised immune competence. It remains unknown however, whether down-regulation of immune genes affects resistance of Atlantic salmon to pathogens and if recovery takes place in seawater. It is also important to figure out if immune suppression is linked to and a consequence of breeding for rapid growth.

RNA-Seq analysis in gills of atlantic salmon (Salmo salar) infected with newly identified ISAV strains in the atlantic Canada region

The Infectious salmon anemia virus (ISAV) is an important viral disease of farmed Atlantic salmon (Salmo salar) which has caused severe financial losses for salmon farmers around the world, including Atlantic Canada. It is listed as an OIE notifiable disease and to this day eradication of infected cages remains the current practice in many countries to mitigate the spread of the virus. All strains known to display any level of virulence are characterised by deletions in the highly polymorphic region (HPR) of the hemagglutinin-esterase (HE) protein compared to ISAV-HPR0 strains and are designated ISAVHPR∆. In contrast, HPR0 strains are non-virulent and not detected by viral culture. In Atlantic Canada, improved management and husbandry practices resulted in no outbreaks caused by ISAV-HPR∆ strains from 2007 to 2012, with however ISAV-HPR0 strains (European genotype) still being detected. Starting in 2012, new ISAV-HPR∆ strains were responsible for disease outbreaks in fish farms in Nova Scotia, Newfoundland and New-Brunswick. This study was thus designed to characterize virulence associated to three of the newly identified ISAV-HPR∆ strains and investigate gene expression responses in gills of infected fish using RNA-Seq. All three ISAV-HPR∆ strains studied through the use of in vivo challenges resulted in cumulative mortalities below 40 percent and caused the differential expression of up to 1000 genes at the peak of infection compared to non-infected fish. Many genes linked to innate immunity were over-expressed; similar to what had been observed in the head-kidney through previous work. The use of RNA-Seq also enabled us to look at ISAV transcript abundance and showed that segment 8 had the highest abundance of all 8 segments of the genome. This information has given us great insight on how ISAV interacts with his host during the course of an infection.

Characterisation of transcription factors in rainbow trout potentially involved in dendritic cell maturation and activation

Dendritic cells (DCs) are heterogeneous cell populations derived from the bone marrow in mammals and play essential roles in antigen presentation and activation of innate and adaptive immune responses after infection. Phenotyping DCs mainly relies on expression of multiple cell surface markers, making it difficult for comparative studies in different species. Recently several transcription factors (TFs) controlling DC differentiation and maturation have been characterised in humans and mice and are highly conserved. These include zinc finger and BTB domain containing 46 (Zbtb46), zinc finger protein 366 (Znf366) and basic leucine zipper transcription factor/ATF-like 3 (Batf3). To search for common molecular markers to assist identification of DC like cells in fish, in this study the gene homologues for these DC-TFs were sequenced in rainbow trout and their phylogeny was analysed. Gene expression was studied in tissues of healthy fish and in gills of Atlantic salmon after exposure to Paramoeba perurans. Furthermore, monocytes/macrophages were isolated from rainbow trout and cultured in the presence of recombinant interleukin 4/13 for 7 days and then examined for DC-TF expression after stimulation with Toll-like receptor ligands such as lipopolysaccharide, bacterial flagellin, polyI:C and imidazoquinoline.

Morphological diversity of Paramoeba perurans trophozoites and their interaction with Atlantic salmon, Salmo salar L., gills.

Amoebic gill disease (AGD) caused by the ectoparasite Paramoeba perurans affects several cultured marine fish species worldwide. In this study, the morphology and ultrastructure of P.perurans invitro and invivo was investigated using scanning and transmission electron microscopy (SEM and TEM, respectively). Amoebae cultures contained several different morphologies ranging from a distinct rounded cell structure and polymorphic cells with pseudopodia of different lengths and shapes. SEM studies of the gills of AGD-affected Atlantic salmon, Salmo salar L., revealed the presence of enlarged swellings in affected gill filaments and fusion of adjacent lamellae. Spherical amoebae appeared to embed within the epithelium, and subsequently leave hemispherical indentations with visible fenestrations in the basolateral surface following their departure. These fenestrated structures corresponded to the presence of pseudopodia which could be seen by TEM to penetrate into the epithelium. The membrane-membrane interface contained an amorphous and slightly fibrous matrix. This suggests the existence of cellular glycocalyces and a role for extracellular products in mediating pathological changes in amoebic gill disease.

A longitudinal study of amoebic gill disease on a marine Atlantic salmon farm utilising a real-time PCR assay for the detection of Neoparamoeba perurans

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 7:239-251 (2015) - DOI: https://doi.org/10.3354/aei00150 A longitudinal study of amoebic gill disease on a marine Atlantic salmon farm utilising a real-time PCR assay for the detection of Neoparamoeba perurans J. K. Downes1,2,*, K. Henshilwood1, E. M. Collins1, A. Ryan3, I. O’Connor2, H. D. Rodger4, E. MacCarthy2, N. M. Ruane1 1Fish Health Unit, Marine Institute, Rinville, Oranmore, Co. Galway, Ireland 2Marine & Freshwater Research Centre, Galway Mayo Institute of Technology, Dublin Road, Galway, Ireland 3Marine Harvest Ireland, Castletownbere, Co. Cork, Ireland 4Vet Aqua International, Unit 7b, Oranmore Business Park, Oranmore, Co. Galway, Ireland *Corresponding author: jamie.downes@marine.ie ABSTRACT: Amoebic gill disease (AGD) is a proliferative gill disease of marine cultured Atlantic salmon Salmo salar, with the free-living protozoan Neoparamoeba perurans being the primary aetiological agent. The increased incidence of AGD in recent years presents a significant challenge to the Atlantic salmon farming industry in Europe. In this study, a real-time TaqMan® PCR assay was developed and validated to detect Neoparamoeba perurans on Atlantic salmon gills and further used to monitor disease progression on a marine Atlantic salmon farm in Ireland in conjunction with gross gill pathology and histopathology. The assay proved specific for N. perurans, with no cross-reactivity with the related species N. pemaquidensis, N. branchiphila or N. aestuarina, and was capable of detecting 2.68 copies of N. perurans DNA µl-1. Although the parasite was detected throughout the 18 mo period of this study, mortality peaks associated with clinical AGD were only recorded during the first 12 mo of the marine phase of the production cycle. The initial AGD outbreak resulted in peak mortality in Week 17, which was preceded by PCR detections from Week 13 onwards. Freshwater treatments were an effective method for controlling the disease, resulting in a reduction in the weekly mortality levels and also a reduction in the number of PCR-positive fish. In comparison to traditional diagnostic methods, our PCR assay proved to be highly sensitive and a valuable tool to monitor disease progression and, therefore, has the potential to provide information on the timing and effectiveness of treatments. KEY WORDS: Amoebic gill disease · Neoparamoeba perurans · Diagnostics · Atlantic salmon Full text in pdf format PreviousNextCite this article as: Downes JK, Henshilwood K, Collins EM, Ryan A and others (2015) A longitudinal study of amoebic gill disease on a marine Atlantic salmon farm utilising a real-time PCR assay for the detection of Neoparamoeba perurans. Aquacult Environ Interact 7:239-251. https://doi.org/10.3354/aei00150 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 7, No. 3. Online publication date: November 18, 2015 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2015 Inter-Research.

Salmon Gill Poxvirus, the Deepest Representative of the Chordopoxvirinae.

ABSTRACTPoxviruses are large DNA viruses of vertebrates and insects causing disease in many animal species, including reptiles, birds, and mammals. Although poxvirus-like particles were detected in diseased farmed koi carp, ayu, and Atlantic salmon, their genetic relationships to poxviruses were not established. Here, we provide the first genome sequence of a fish poxvirus, which was isolated from farmed Atlantic salmon. In the present study, we used quantitative PCR and immunohistochemistry to determine aspects of salmon gill poxvirus disease, which are described here. The gill was the main target organ where immature and mature poxvirus particles were detected. The particles were detected in detaching, apoptotic respiratory epithelial cells preceding clinical disease in the form of lethargy, respiratory distress, and mortality. In moribund salmon, blocking of gas exchange would likely be caused by the adherence of respiratory lamellae and epithelial proliferation obstructing respiratory surfaces. The virus was not found in healthy salmon or in control fish with gill disease without apoptotic cells, although transmission remains to be demonstrated. PCR of archival tissue confirmed virus infection in 14 cases with gill apoptosis in Norway starting from 1995. Phylogenomic analyses showed that the fish poxvirus is the deepest available branch of chordopoxviruses. The virus genome encompasses most key chordopoxvirus genes that are required for genome replication and expression, although the gene order is substantially different from that in other chordopoxviruses. Nevertheless, many highly conserved chordopoxvirus genes involved in viral membrane biogenesis or virus-host interactions are missing. Instead, the salmon poxvirus carries numerous genes encoding unknown proteins, many of which have low sequence complexity and contain simple repeats suggestive of intrinsic disorder or distinct protein structures.IMPORTANCE Aquaculture is an increasingly important global source of high-quality food. To sustain the growth in aquaculture, disease control in fish farming is essential. Moreover, the spread of disease from farmed fish to wildlife is a concern. Serious poxviral diseases are emerging in aquaculture, but very little is known about the viruses and the diseases that they cause. There is a possibility that viruses with enhanced virulence may spread to new species, as has occurred with the myxoma poxvirus in rabbits. Provision of the first fish poxvirus genome sequence and specific diagnostics for the salmon gill poxvirus in Atlantic salmon may help curb this disease and provide comparative knowledge. Furthermore, because salmon gill poxvirus represents the deepest branch of chordopoxvirus so far discovered, the genome analysis provided substantial insight into the evolution of different functional modules in this important group of viruses.

The interbranchial lymphoid tissue of Atlantic Salmon (Salmo salar L) extends as a diffuse mucosal lymphoid tissue throughout the trailing edge of the gill filament.

The teleost gill forms an extensive, semipermeable barrier that must tolerate intimate contact with the surrounding environment and be able to protect the body from external pathogens. The recent discovery of the interbranchial lymphoid tissue (ILT) has initiated an anatomical and functional investigation of the lymphoid tissue of the salmonid gill. In this article, sectioning of gill arches in all three primary planes revealed an elongation of the ILT outward along the trailing edge of the primary filament to the very distal end, a finding not previously described. This newly found lymphoid tissue was investigated using a range of morphological and transcriptional tools. Avoiding potential salinity-related effects, the study focused on two fresh-water life stages-smoltifying juveniles and mature adults. Aggregates of T-cells continuous with the ILT were found within the thick epithelial lining of the trailing edge of the filament in considerably larger numbers than seen in the epithelium of the leading edge and of the interlamellar area. Only a few of these cells were identified as CD8α(+) -cells, and there was a significantly (P < 0.05) higher relative expression of CD4- than of CD8- related genes in all gill segments investigated. Numerous major histocompatibility complex class II(+) -cells were distributed uniformly throughout the filament epithelial tissue. Few Ig(+) -cells were detected. Overall, the morphological features and comparable immune gene expression of the previously described ILT and the filament trailing edge lymphoid tissue suggest a close functional and anatomical relationship. We propose that the anatomical definition of the ILT must be broadened to include both the previously described ILT (to be renamed proximal ILT) and the trailing edge lymphoid tissue (to be named distal ILT). This extended anatomical localisation identifies the ILT as a widely distributed mucosal lymphoid tissue in the gill of Atlantic salmon.

Use of otolith microchemistry and stable isotopes to investigate the ecology and anadromous migrations of Northern Dolly Varden from the Egegik River, Bristol Bay, Alaska

Dolly Varden (Salvelinus malma) is a facultatively anadromous and iteroparous salmonid species, widely distributed around the Pacific Rim. Its distribution overlaps in northern areas with the circumpolar congeneric Arctic char (S. alpinus), which shares some of its life history traits. Despite the abundance of both species in many Alaskan watersheds and the diversity of their life histories, relatively little is known about their estuarine and marine ecology and migrations. Thirty char, taken as by-catch in the sockeye salmon (Oncorhynchus nerka) gill net fishery in the Egegik District, Bristol Bay, Alaska in June and July 2013, were identified using molecular genetic techniques as Dolly Varden. Otoliths indicated that the fish, ranging from 445 to 560 mm fork length, were from 4 to 9 years old, with a modal age of 6 (40 % of the specimens). Microchemical analysis indicated that all fish had first migrated to sea at ages 2 or 3 (16 and 14 individuals, respectively), migrated annually thereafter to a maximum of eight times, and did not over-winter in marine waters. Moreover, the fish were produced by a mix of anadromous mothers (14 fish) and non-anadromous mothers (11 fish); the maternal origin of the other five fish was uncertain. Despite the fact that the fish were captured in the riverine/estuarine environment of the Egegik River, stable isotope analysis of muscle tissue samples indicated that they had relied on marine prey, and this was supported by the high Sr levels in the otoliths, indicating prior occupancy of marine rather than fresh water for all individuals tested. Together, these analyses reveal extensive use of marine resources by Dolly Varden across a wide range of sizes and ages during regular but brief migrations, and provide new information on this facultatively anadromous, long-lived salmonid.

Characterization of 'Candidatus Syngnamydia salmonis' (Chlamydiales, Simkaniaceae), a bacterium associated with epitheliocystis in Atlantic salmon (Salmo salar L.).

Two Chlamydiales have previously been found to infect Atlantic salmon (Salmo salar L.), Candidatus Piscichlamydia salmonis and Candidatus Clavichlamydia salmonicola. Both develop intracellularly in cyst-like inclusions in gill cells, generally referred to as epitheliocysts. Here, we present evidence for the association of a novel species of Chlamydiales with epitheliocystis in Atlantic salmon. Based on its partial 16S rRNA gene sequence, it is a new member of the family Simkaniaceae, and a 95.7 % identity to the type species Candidatus Syngnamydia venezia suggests inclusion in the candidate genus Syngnamydia. The presence of the bacterium in epitheliocysts in gills of Atlantic salmon was demonstrated by RNA–RNA hybridization. Ultrastructurally, the novel bacterium produces pleomorphic reticulate bodies and elementary bodies (EBs) with a characteristic morphology. The EBs are short rods with a terminal disc-like cap area, a sub-apical spherical vacuole-like electron-lucent structure and a post-equatorial nucleoid. We propose the name Candidatus Syngnamydia salmonis for this new agent from epitheliocysts in seawater-reared salmon .