Gills Of Salmon Research Articles

Epidemiology of marine gill diseases in Atlantic salmon (Salmo salar) aquaculture: a review

AbstractGill disease of farmed Atlantic salmon (Salmo salar) in the marine environment has emerged as a significant problem for the salmon aquaculture industry. Different types of marine salmon gill disease reported include amoebic gill disease (AGD), parasitic gill disease, viral gill disease, bacterial gill disease, zooplankton (cnidarian nematocyst)‐associated gill disease, harmful algal gill disease and chemical/toxin‐associated gill disease. The term ‘multifactorial gill disease’ is used when multiple distinguishable types of disease (as opposed to an obvious single primary type) are present. When gill disease is non‐specific, it is referred to as ‘complex gill disease’ (CGD) or ‘complex gill disorder’. These two terms are often used interchangeably and are overlapping. The significance of many infectious and non‐infectious agents that may be associated with CGD is often unclear. In this review, we summarise aspects of the different types of gill disease that are relevant to the epidemiology of gill disease and of CGD in particular. We also tabulate simultaneously occurring putative pathogens to explore the multifactorial nature of gill disease.

Genotyping of Salmon Gill Poxvirus Reveals One Main Predominant Lineage in Europe, Featuring Fjord- and Fish Farm-Specific Sub-Lineages.

Salmon gill poxvirus (SGPV) can cause serious gill disease in Atlantic salmon (Salmo salar L.) and represents a significant problem to aquaculture industries in Northern Europe. Here, a single-tube multi-locus variable-number tandem-repeat (VNTR) analysis (MLVA) genotyping assay, targeting eight VNTR loci, was developed for studying the epizootiology of SGPV. Through MLVA typing of SGPV positive samples from 180 farmed and wild Atlantic salmon in Northern Europe, the first molecular population study of this virus was undertaken. Comparison of resulting MLVA profiles by cluster analysis revealed considerable micro-diversity, while only a limited degree of specific clustering by country of origin could be observed, and no clustering relating to the severity of disease outbreaks. Phylogenetic analysis, based on genomic data from six SGPV specimens (three Norwegian, one Scottish, one Faroese and one Canadian), complemented and corroborated MLVA by pointing to a marked transatlantic divide in the species, with one main, relatively conserved, SGPV lineage as predominant in Europe. Within certain fjord systems and individual freshwater salmon smolt farms in Norway, however, discrete MLVA clustering patterns that prevailed over time were observed, likely reflecting local predominance of specific SGPV sub-lineages. MLVA typing was also used to refute two suspected instances of vertical SGPV transmission from salmon broodstock to offspring, and to confirm a failed disinfection attempt in one farm. These novel insights into the previously undocumented population structure of SGPV provide important clues, e.g., regarding the mechanisms underlying spread and recurrence of the virus amongst wild and farmed salmon populations, but so far no indications of more or less virulent SGPV sub-lineages have been found. The MLVA scheme represents a highly sensitive genotyping tool particularly well suited for illuminating SGPV infection routes, and adds to the relatively low number of MLVA protocols that have so far been published for viral species. Typing is reasonably inexpensive, with a moderate technological requirement, and may be completed within a single working day. Resulting MLVA profiles can be readily shared and compared across laboratories, facilitating rapid placement of samples in an international ezpizootiological context.

First record of experimentally induced salmon gill poxvirus disease (SGPVD) in Atlantic salmon (Salmo salar L.)

Salmon gill poxvirus (SGPV) infection is a common denominator in many cases of complex gill disease in the Norwegian salmon farming industry and may, as a single agent infection, result in salmon poxvirus disease (SGPVD). Experiences from the field suggest that stress may be a decisive factor for the induction of SGPVD. Here we investigated the effect of stress hormone treatment on SGPV kinetics and disease development. In our experiment, Atlantic salmon were divided into four groups. Two groups of fish received an intraperitoneal injection of hydrocortisone dissolved in a fatty vehicle, whereas fish in the other two groups received a sham injection of the vehicle. After 24 h, one group with hydrocortisone injection and one with sham injection were exposed to dead SGPV-infected fish. Plasma cortisol level, virus kinetics, virus localization, and pathological gill were monitored for 4 weeks post-exposure. Hydrocortisone injected fish displayed higher plasma cortisol and SGPV loads than non-hydrocortisone treated fish. Signs of SGPVD and ensuing mortality appeared only in fish exposed to the virus and injected with hydrocortisone around 2 weeks post-exposure. No clinical signs of disease or mortality were recorded in the other groups. Further, gill histopathology in diseased fish correlated well with SGPV load, with the infection apparently confined to gill epithelial cells. The current findings suggest elevated plasma cortisol being a prerequisite for the development of SGPVD and recommend minimization of stressful farming activities, particularly if SGPV infection has been previously identified.

Histopathological investigation of complex gill disease in sea farmed Atlantic salmon.

Various agents including Ca. Piscichlamydia salmonis, Ca. Branchiomonas cysticola, Desmozoon lepeophtherii, Paramoeba perurans and salmon gill poxvirus may be associated with complex gill disease in Atlantic salmon. Co-infections involving two or more of these agents are common and histopathological interpretation of lesions is therefore challenging. In this study, we developed a semi-quantitative scoring system for examination of histopathological gill lesions in sea-farmed Atlantic salmon suffering from gill disease. Following qPCR analysis of gills sampled for Ca. P. salmonis, Ca. B. cysticola, D. lepeophtherii and P. perurans from 22 geographically spread outbreaks, five cases representing different infectious loads and combinations of agents were chosen for histopathological scoring. Twenty-eight histological features were evaluated and potential associations between individual pathological changes and the occurrence of individual agents studied. The inter-observer agreement in interpretation of histological parameters between the three pathologists involved, was calculated to validate robustness of the scoring scheme. Seventeen histological parameters met the criteria for inter-observer agreement analysis and were included in the calculation. The three most frequent findings were identification of subepithelial leukocytes, epithelial cell hyperplasia and mucus cell hyperplasia. While few findings could be specifically related to particular agents, necrosis in hyperplastic lesions, pustules and necrosis of subepithelial cells appeared to be associated with the presence of Ca. B. cysticola. Further, lesion profiles clearly support the previously identified association between P. perurans and pathological changes associated with AGD. Very few pathological changes were observed in the single case in which Ca. P. salmonis was the dominating agent. Some lesions were only very rarely observed e.g. chloride cell necrosis, epithelial cell apoptosis, lamellar deposition of melanin and haemophagocytosis. The scoring scheme developed and applied was robust and sensitive. A less extensive scheme for routine diagnostic use is proposed.

Prevalence of six amoeba species colonising the gills of farmed Atlantic salmon with amoebic gill disease (AGD) using qPCR

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 11:405-415 (2019) - DOI: https://doi.org/10.3354/aei00325 Prevalence of six amoeba species colonising the gills of farmed Atlantic salmon with amoebic gill disease (AGD) using qPCR Chloe J. English1,2,*, Fiona Swords3, Jamie K. Downes3, Neil M. Ruane3, Natasha A. Botwright4, Richard S. Taylor5, Andrew C. Barnes1, James W. Wynne5, Paula C. Lima4, Mathew T. Cook4 1School of Biological Sciences, The University of Queensland, Brisbane, QLD 4072, Australia 2CSIRO Agriculture and Food, Aquaculture, Bribie Island Research Centre, 144 North Street, Woorim, QLD 4507, Australia 3Marine Institute, Rinville, Oranmore, H91 R673 Co. Galway, Ireland 4CSIRO Agriculture and Food, Aquaculture, Queensland Biosciences Precinct, 306 Carmody Road, St Lucia, QLD 4067, Australia 5CSIRO Agriculture and Food, Aquaculture, Castray Esplanade, Battery Point, TAS 7004, Australia *Corresponding author: chloe.english@csiro.au ABSTRACT: Amoebic gill disease (AGD) is the primary health concern for Atlantic salmon Salmo salar farmed in Tasmania, Australia. Neoparamoeba perurans is the aetiological agent of AGD; however, a diversity of other amoebae colonise the gills, and their role in AGD is unknown. Previous studies which document these accompanying amoebae on AGD-affected farmed Atlantic salmon relied on culture-based techniques which do not accurately determine the prevalence and abundance of these species nor whether they correlate with AGD pathology. Drawing on our previous culture-based study, here we develop and apply 5 new Taqman quantitative PCR (qPCR) assays to profile the prevalence of multiple amoeba species on the gills of AGD-affected Atlantic salmon held at 2 Tasmanian farm sites over a 1 yr period. The prevalence and abundance of N. perurans was also assessed using a previously established qPCR method. N. perurans was the dominant species, and its abundance positively correlated with the progression of gross gill pathology. Only a small number of sporadic detections of Pseudoparamoeba and Vannellida species were observed. Nolandella spp. was the notable exception, as it was the most prevalent amoeba (92%) at 1 site at 1 sample time, during which no N. perurans were detected on gills but low levels of gross gill pathology were observed. N. perurans is the predominant species and primary pathogen of AGD; however, there were instances when they were not detected on diseased gills and Nolandella spp. were highly prevalent. The significance of Nolandella spp. in relation to AGD is not yet understood. KEY WORDS: Neoparamoeba · Nolandella · Amoebozoa · AGD · Taqman qPCR · Atlantic salmon Full text in pdf format Supplementary material PreviousNextCite this article as: English CJ, Swords F, Downes JK, Ruane NM and others (2019) Prevalence of six amoeba species colonising the gills of farmed Atlantic salmon with amoebic gill disease (AGD) using qPCR. Aquacult Environ Interact 11:405-415. https://doi.org/10.3354/aei00325 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: August 22, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.

Changes in distribution, morphology and ultrastructure of chloride cell in Atlantic salmon during an AGD infection.

Amoebic gill disease (AGD) is emerging as one of the most significant health challenges affecting farmed Atlantic salmon in the marine environment. It is caused by the amphizoic amoeba Neoparamoeba perurans, with infestation of gills causing severe hyperplastic lesions, compromising overall gill integrity and function. This study used histology, transmission electron microscopy (TEM), immunohistochemistry and transcript expression to relate AGD-associated pathological changes to changes in the morphology and distribution of chloride cells (CCs) in the gills of Atlantic salmon (Salmo salar L.) showing the progression of an AGD infection. A marked reduction in numbers of immunolabelled CCs was detected, and a changing pattern in distribution and morphology was closely linked with the level of basal epithelial hyperplasia in the gill. In addition, acute degenerative ultrastructural changes to CCs at the lesion site were observed with TEM. These findings were supported by the early-onset downregulation of Na+ /K+ -ATPase transcript expression. This study provides supportive evidence that histological AGD lesion assessment was a good qualitative tool for AGD scoring and corresponded well with qPCR genomic Paramoeba perurans quantification. Ultrastructural changes induced in salmon CCs as a result of AGD are reported here for the first time.

Cloning of selected body surface antimicrobial peptide/protein genes of Atlantic salmon and their responses to Aeromonas salmonicida

Antimicrobial peptides/proteins (AMPs), the important host-defence molecules with antimicrobial and immunomodulatory properties, effectively ward off pathogenic organisms. The responses of such molecules of Atlantic salmon during Aeromonas salmonicida infection that causes losses to salmon farms are not clearly described. Two trials were carried out to understand the regulation of two known AMP genes (cathelicidins, cath1, 2) and five newly cloned AMP genes (beta-defensins, defb1-4 and l-amino acid oxidase, lao); in vivo responses following intraperitoneal injection of A. salmonicida vaccine and in vitro responses upon exposure of gill tissues to A. salmonicida. The vaccine injection induced cath1, cath2 and lao expression in the gills at 24 h post injection. The live A. salmonicida exposure of Atlantic salmon gill tissue explant revealed the upregulation of the cath1 and cath2 within 48 h. The defb genes were not altered by either injection or exposure to A. salmonicida. Based on the evidence we suggest that the cathelicidins (cath1 and cath2) are A. salmonicida-inducible AMPs and could be possible biomarkers of infection.

Gill diseases in marine salmon aquaculture with an emphasis on amoebic gill disease.

Abstract Gill diseases are a growing health challenge in salmon farming worldwide, but many gaps remain in our knowledge. Gill diseases are generally complex and multifactorial disorders, often with presumable spatial and temporal distribution patterns, but are highly difficult to effectively prevent and control. The term complex gill disease (CGD) includes a wide range of clinical disease presentations on the gills of farmed salmon; usually, CGD presents from the end of summer to early winter. The pathogens involved include Neoparamoeba perurans , Tenacibaculum maritimum , Candidatus Piscichlamydia salmonis , Candidatus Branchiomonas cysticola , Desmozoon lepeophtherii (syn. Paranucleospora theridion ) and viruses, such as the Atlantic salmon paramyxovirus (ASPV) and salmon gill poxvirus (SGPV). Amoebic gill disease (AGD) is perhaps the most significant disease in terms of gill health and economic impact. AGD results in high mortality, reduced production performance and impaired fish welfare. This review summarizes and analyses CGD research, outbreaks and treatment, with a focus on AGD, as well as on knowledge gaps and avenues for future research.

Isolation and identification of a novel salmon gill poxvirus variant from Atlantic salmon in Eastern Canada

Isolation and identification of a novel salmon gill poxvirus variant from Atlantic salmon in Eastern Canada

Contrasting effects of acute and chronic stress on the transcriptome, epigenome, and immune response of Atlantic salmon

ABSTRACTStress experienced during early life may have lasting effects on the immune system, with impacts on health and disease dependent on the nature and duration of the stressor. The epigenome is especially sensitive to environmental stimuli during early life and represents a potential mechanism through which stress may cause long-lasting health effects. However, the extent to which the epigenome responds differently to chronic vs acute stressors is unclear, especially for non-mammalian species. We examined the effects of acute stress (cold-shock during embryogenesis) and chronic stress (absence of tank enrichment during larval-stage) on global gene expression (using RNA-seq) and DNA methylation (using RRBS) in the gills of Atlantic salmon (Salmo salar) four months after hatching. Chronic stress induced pronounced transcriptional differences, while acute stress caused few lasting transcriptional effects. However, both acute and chronic stress caused lasting and contrasting changes in the methylome. Crucially, we found that acute stress enhanced transcriptional immune response to a pathogenic challenge (bacterial lipopolysaccharide, LPS), while chronic stress suppressed it. We identified stress-induced changes in promoter and gene-body methylation that were associated with altered expression for a small proportion of immune-related genes, and evidence of wider epigenetic regulation within signalling pathways involved in immune response. Our results suggest that stress can affect immuno-competence through epigenetic mechanisms, and highlight the markedly different effects of chronic larval and acute embryonic stress. This knowledge could be used to harness the stimulatory effects of acute stress on immunity, paving the way for improved stress and disease management through epigenetic conditioning.

Effects of repeated anaesthesia on gill and general health of Atlantic salmon, Salmo salar.

Fish are the second most widely utilized vertebrate group used for scientific procedures in the United Kingdom, but the development and application of 3Rs (the principles of replacement, reduction, and refinement) in aquaculture disease research lags behind methodologies in place for mammalian studies. With a need for individual monitoring and non-lethal sampling, the effect of repeat anaesthesia on experimental fish needs to be better understood. This study analyses the effect of repeat anaesthesia with MS-222, metomidate and AQUI-S upon the gill and general health of post-smolt Atlantic salmon Salmo salar. A single, lethal dose of anaesthetic was compared with seven anaesthetizing time points over 28 days, terminating in a lethal dose. No anaesthetic showed significant differences in accumulation in the muscle tissue, or changes in plasma glucose after repeated or single dosing. Fish repeatedly anaesthetized with MS-222 or AQUI-S exhibited upregulation of osmoregulatory genes in the gill and AQUI-S-treated individuals showed, histologically, epithelial lifting from the lamellae capillary irrespective of whether they had a single or repeated dose history. No significant changes were seen in inflammatory or stress genes in the head kidney of fish repeatedly anaesthetized with AQUI-S or metomidate, however MS-222 treatment resulted in upregulation of tnfα3. Repeated anaesthesia with MS-222 and metomidate gave a significant decrease and increase in peripheral blood neutrophils, respectively. This study concludes that no increase in cumulative stress or inflammation is induced by the repeated anaesthetization of S. salar with any of the tested anaesthetics, however gill osmotic regulation and blood parameters may be affected.

The 2.1 \xc5 structure of protein F9 and its comparison to L1, two components of the conserved poxvirus entry-fusion complex

The poxvirus F9 protein is a component of the vaccinia virus entry fusion complex (EFC) which consists of 11 proteins. The EFC forms a unique apparatus among viral fusion proteins and complexes. We solved the atomic structure of the F9 ectodomain at 2.10 Å. A structural comparison to the ectodomain of the EFC protein L1 indicated a similar fold and organization, in which a bundle of five α-helices is packed against two pairs of β-strands. However, instead of the L1 myristoylation site and hydrophobic cavity, F9 possesses a protruding loop between α-helices α3 and α4 starting at Gly90. Gly90 is conserved in all poxviruses except Salmon gill poxvirus (SGPV) and Diachasmimorpha longicaudata entomopoxvirus. Phylogenetic sequence analysis of all Poxviridae F9 and L1 orthologs revealed the SGPV genome to contain the most distantly related F9 and L1 sequences compared to the vaccinia proteins studied here. The structural differences between F9 and L1 suggest functional adaptations during evolution from a common precursor that underlie the present requirement for each protein.

Gene expression analysis of Atlantic salmon gills reveals mucin 5 and interleukin 4/13 as key molecules during amoebic gill disease

Amoebic gill disease (AGD) is one of the main diseases affecting Atlantic salmon (Salmo salar L.) mariculture. Hallmarks of AGD are hyperplasia of the lamellar epithelium and increased production of gill mucus. This study investigated the expression of genes involved in mucus secretion, cell cycle regulation, immunity and oxidative stress in gills using a targeted 21-gene PCR array. Gill samples were obtained from experimental and natural Neoparamoeba perurans infections, and sampling points included progressive infection stages and post-freshwater treatment. Up-regulation of genes related to mucin secretion and cell proliferation, and down-regulation of pro-inflammatory and pro-apoptotic genes were associated with AGD severity, while partial restoration of the gill homeostasis was detected post-treatment. Mucins and Th2 cytokines accoun ted for most of the variability observed between groups highlighting their key role in AGD. Two mucins (muc5, muc18) showed differential regulation upon disease. Substantial up-regulation of the secreted muc5 was detected in clinical AGD, and the membrane bound muc18 showed an opposite pattern. Th2 cytokines, il4/13a and il4/13b2, were significantly up-regulated from 2 days post-infection onwards, and changes were lesion-specific. Despite the differences between experimental and natural infections, both yielded comparable results that underline the importance of the studied genes in the respiratory organs of fish, and during AGD progression.

Complex Gill Disease: an Emerging Syndrome in Farmed Atlantic Salmon (Salmo salar L.)

Gill disorders have become a significant problem during the marine phase of farming Atlantic salmon (Salmo salar L.). The term complex gill disease (CGD) includes a wide range of clinical gill disease presentations generally occurring from the end of summer to early winter on marine Atlantic salmon farms. The gross and histological lesions observed are the resultant culmination of exposure to a mixture of environmental insults, pathogenic organisms and farm management practices. None of the three principal agents purportedly associated with CGD (Desmozoon lepeophtherii, salmon gill poxvirus or Candidatus Branchiomonas cysticola) have been cultured successfully in-vitro, so individual in-vivo challenge studies to identify their pathogenesis have not been possible. Studies of cohabitation of single pathogen-infected fish with naïve fish, and epidemiological investigations are required urgently to elucidate the roles of these pathogens and other factors in CGD.

Effects of cnidarian biofouling on salmon gill health and development of amoebic gill disease.

This study examines the potential implications of biofouling management on the development of an infectious disease in Norwegian farmed salmon. The hydroid Ectopleura larynx frequently colonises cage nets at high densities (thousands of colonies per m2) and is released into the water during regular in-situ net cleaning. Contact with the hydroids’ nematocysts has the potential to cause irritation and pathological damage to salmon gills. Amoebic gill disease (AGD), caused by the amoeba Paramoeba perurans, is an increasingly international health challenge in Atlantic salmon farming. AGD often occurs concomitantly with other agents of gill disease. This study used laboratory challenge trials to: (1) characterise the gill pathology resulting from the exposure of salmon to hydroids, and (2) investigate if such exposure can predispose the fish to secondary infections–using P. perurans as an example. Salmon in tanks were exposed either to freshly ‘shredded’ hydroids resembling waste material from net cleaning, or to authentic concentrations of free-living P. perurans, or first to ‘shredded’ hydroids and then to P. perurans. Gill health (AGD gill scores, non-specific gill scores, lamellar thrombi, epithelial hyperplasia) was monitored over 5 weeks and compared to an untreated control group.Nematocysts of E. larynx contained in cleaning waste remained active following high-pressure cleaning, resulting in higher non-specific gill scores in salmon up to 1 day after exposure to hydroids. Higher average numbers of gill lamellar thrombi occurred in fish up to 7 days after exposure to hydroids. However, gill lesions caused by hydroids did not affect the infection rates of P. perurans or the disease progression of AGD. This study discusses the negative impacts hydroids and current net cleaning practices can have on gill health and welfare of farmed salmon, highlights existing knowledge gaps and reiterates the need for alternative approaches to net cleaning.

Differences in fatty acid composition of gill and liver phospholipids between Steelhead trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) under declining temperatures

This study investigated the fatty acid (FA) composition of gill and liver phospholipids in Steelhead trout (Oncorhynchus mykiss) (average weight: 75.45 ± 6.27 g) and Atlantic salmon (Salmo salar) (average weight: 72.89 ± 3.12 g) as water temperature decreased from 16 °C to 12 °C, 8 °C, 6 °C, 4 °C, 2 °C, and 1 °C. At normal temperature (16 °C), both gill and liver phospholipids of Atlantic salmon had lower saturated fatty acid (SFA) and higher unsaturated (UFA) compositions than those of Steelhead trout. Atlantic salmon was more sensitive to the temperature decline than Steelhead trout at the early stage of the experiment. Polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of Atlantic salmon liver phospholipids significantly increased as temperature decreased from 16 °C to 12 °C. However, both PUFA and MUFA contents decreased significantly at temperatures below 4 °C. In contrast, there was only a negligible decrease in MUFA content in Steelhead trout liver phospholipids at 1 °C. Starvation and cold stress influenced liver phospholipid FA composition in Atlantic salmon but not in Steelhead trout, suggesting that the latter can better adapt to low temperatures. Changes in gill phospholipid composition in response to temperature fluctuations were species-specific. When the ambient temperature was below 8 °C, SFA content of gill phospholipids decreased whereas PUFA content increased and MUFA content was unaltered in Atlantic salmon. Although the FA composition of gill phospholipids in Atlantic salmon was altered at 6 °C, it remained stable as temperature further decreased. These results indicate that the FA composition of gill phospholipids in Atlantic salmon is less influenced by starvation stress than that of liver phospholipids. Moreover, fewer changes in FA composition were observed for gill as compared to liver phospholipids in both species of fish. Our results can be useful for optimizing Atlantic salmon and Steelhead trout aquaculture systems.

Investigation of co-infections with pathogens associated with gill disease in Atlantic salmon during an amoebic gill disease outbreak.

Gill diseases are a complex and multifactorial challenge for marine farmed Atlantic salmon. Co-infections with putative pathogens are common on farms; however, there is a lack of knowledge in relation to the potential effect co-infections may have on pathology. The objective of this study was to determine the prevalence and potential effects of Neoparamoeba perurans, Desmozoon lepeophtherii, Candidatus Branchiomonas cysticola, Tenacibaculum maritimum and salmon gill poxvirus (SGPV) during a longitudinal study on a marine Atlantic salmon farm. Real-time PCR was used to determine the presence and sequential infection patterns of these pathogens on gill samples collected from stocking until harvest. A number of multilevel models were used to determine the effect of these putative pathogens on gill health (measured as gill histopathology score), while adjusting for the effect of water temperature and time since the last freshwater treatment. Results indicate that between 12 and 16weeks post-seawater transfer (wpst), colonization of the gills by all pathogens had commenced and by week 16 of marine production each of the pathogens had been detected. D.lepeophtherii and Candidatus B. cysticola were by far the most prevalent of the potential pathogens detected during this study. Detections of T.maritimum were found to be significantly correlated with temperature showing distinct seasonality. Salmon gill poxvirus was found to be highly sporadic and detected in the first sampling point, suggesting a carryover from the freshwater stage of production. Finally, the model results indicated no clear effect between any of the pathogens. Additionally, the models showed that the only variable which had a consistent effect on the histology score was N.perurans.

Salmon gill poxvirus disease in Atlantic salmon fry as recognized by improved immunohistochemistry also demonstrates infected cells in non-respiratory epithelial cells.

Gill diseases cause serious losses in farming of Atlantic salmon and the number of agents involved increases. Salmon gill poxvirus (SGPV) and the gill disease in causes where SGPV apparently was the only disease-causing agent were initially characterized. Recently, it was further shown that SGPV can be a common denominator in widely different multifactorial gill diseases. Here, we present the challenge of diagnosing gill disease with SGPV in salmon fry of 0,3-5 grams. Apoptosis of gill lamellar epithelial cells and hemophagocytosis was also observed in fry similar to findings in smolts and grow-out fish. Using our newly developed immunohistochemistry method, we further demonstrate that some of the apoptotic epithelial cells covering the oral cavity were positive for SGPV. Thus, SGPV is not restricted to respiratory epithelium alone and may infect the fish at very early life stages. Furthermore, as the cases examined here are from Norway, Faroe Island and Scotland, we show that SGPV is more widespread than previously reported.

BK potassium channel mRNA level changes in gills of Atlantic salmon after brackish water transfer

BK potassium channels are implicated in a variety of physiological processes and they have been characterized in many species from Drosophila to humans although detailed studies about their properties and functions in the osmoregulation of teleosts are still lacking. In this study, we have cloned 911 bp corresponding to a partial Salmo salar BK channel coding sequence with high level of homology to BK channel sequences from other teleosts. Also, we have followed the BK gene expression pattern in gills of Atlantic salmon during brackish water (BW) acclimation. Interestingly, transfer from freshwater to BW induced an upregulation in mRNA BK channel expression in gills 7 days after transfer to BW, followed by a decrease in the expression. These results are the first describing mRNA changes of BK channel in gills of Atlantic salmon during BW acclimation, and they could suggest a possible role for BK channel during this adaptive response. Additionally, our results could position BK potassium channels expressed in the gills of Salmo salar as new candidates to be a marker of smoltification process, which may complement, and possibly outperform NKA activity measurement, the current gold standard of the Chilean industry.

Interspecies variation in the susceptibility of adult Pacific salmon to toxic urban stormwater runoff

Adult coho salmon (Oncorhynchus kisutch) prematurely die when they return from the ocean to spawn in urban watersheds throughout northwestern North America. The available evidence suggests the annual mortality events are caused by toxic stormwater runoff. The underlying pathophysiology of the urban spawner mortality syndrome is not known, and it is unclear whether closely related species of Pacific salmon are similarly at risk. The present study co-exposed adult coho and chum (O. keta) salmon to runoff from a high traffic volume urban arterial roadway. The spawners were monitored for the familiar symptoms of the mortality syndrome, including surface swimming, loss of orientation, and loss of equilibrium. Moreover, the hematology of both species was profiled by measuring arterial pH, blood gases, lactate, plasma electrolytes, hematocrit, and glucose. Adult coho developed behavioral symptoms within a few hours of exposure to stormwater. Various measured hematological parameters were significantly altered compared to coho controls, indicating a blood acidosis and ionoregulatory disturbance. By contrast, runoff-exposed chum spawners showed essentially no indications of the mortality syndrome, and measured blood hematological parameters were similar to unexposed chum controls. We conclude that contaminant(s) in urban runoff are the likely cause of the disruption of ion balance and pH in coho but not chum salmon. Among the thousands of chemicals in stormwater, future forensic analyses should focus on the gill or cardiovascular system of coho salmon. Because of their distinctive sensitivity to urban runoff, adult coho remain an important vertebrate indicator species for degraded water quality in freshwater habitats under pressure from human population growth and urbanization.