Anatomical distribution of scavenger endothelial cells in bony fishes (Osteichthyes).

The scavenger endothelial cells (SECs) of vertebrates are an important class of endocytic cells responsible for clearance of foreign and physiological waste macromolecules, partitioning in the immune system, functioning as a cellular powerplant by producing high energy metabolites like lactate and acetate. All animal phyla possess SECs, but the tissue localization of SECs has only been investigated in a limited number of species. By using a specific ligand for scavenger receptors (formalin treated bovine serum albumin), the study revealed that in all tetrapod species (amphibia, reptiles, birds and mammals) the SECs were found lining the sinusoids of the liver. No SECs were found in the liver of any of the bony fishes (Osteichthyes) investigated. Interestingly, we found the SECs not only to be located in the heart of marine species but also in some freshwater species such as Lota lota, Percichthys trucha and Perca fluviatilis. In some fish species, the SECs were found both in the heart and/or kidney in a number of marine and freshwater fishes, whereas in some marine, diadromous and freshwater fishes the SECs were confined only to the kidney tissue. However, from these results it can be suggested that there is neither a clear phylogenetic trend when it came to anatomical localization of SECs nor any pattern in terms of habitat (salinity preferences).

Characterization of an outbreak of cardiomyopathy syndrome (CMS) in young Atlantic salmon, Salmo salar L.

Cardiomyopathy syndrome (CMS) is the most common viral cardiac disease in Norwegian Atlantic salmon farming and typically affects large, market size fish. Only six months after seawater transfer, Atlantic salmon were diagnosed with CMS at a fish farm in the south-western part of Norway. Due to the unexpected young age and the remarkable large amounts of virus-specific RNA (Ct <10), the fish group was monitored with five additional samplings until slaughtered almost 10 months later. At three weeks after the first CMS diagnosis (weeks post-diagnosis, wpd) and at slaughter (39 wpd), more comprehensive samplings were performed of the study cage, with specific focus on three different cardiac compartments. The clinical, autopsy and histopathological findings at first diagnosis and at all succeeding samplings were similar to previous descriptions of typical CMS. A slightly elevated mortality was observed in the cage with diseased fish at the time of the first CMS diagnosis and continued throughout the study. The prevalence and load of PMCV-specific RNA in the fish remained high until slaughtering, with similar amounts in all sampled cardiac compartments. No fish from the other five cages at the site were diagnosed with CMS, until fish sampled from the last cage at the site were diagnosed 10 weeks after slaughtering of the study cage (49 wpd). Sequence analysis of the PMCV on the site showed that the outbreak virus was similar to PMCV variants previously sequenced from Norwegian field outbreaks. In conclusion, CMS in young Atlantic salmon had clinical signs and histopathological cardiac lesions typical for the disease, and diseased fish could be found in the study cage until slaughtering.

Increasing intensities of Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878) larvae with weight and sea age in returning adult Atlantic salmon, Salmo salar L., of coastal waters of Norway.

Ninety wild Atlantic salmon, Salmo salar L., (1.5-10.3 kg) were caught in the Namsen Fjord near the mouth of River Namsen, mid-Norway, and examined for the presence and distribution of Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878) larvae by digestion of the viscera and muscles in a pepsin/HCl solution. All salmon were migrating spawners after 1-4 years of feeding in the Atlantic Ocean. All 90 Atlantic salmon had A. simplex larvae in the viscera, and all, except two, had A. simplex larvae in the musculature. The number of A. simplex larvae in each fish varied between 3 and 181, and the total mean number of nematode larvae was 44.5. The intensity of A. simplex larvae was positively correlated with increasing weight and sea age of the host. However, the proportion of larvae in the muscle fillets decreased with increasing host weight and sea age. Atlantic salmon females had more A. simplex larvae than males. In all the fish examined, 70.2% of the A. simplex larvae were found in the viscera and 29.8% in the musculature. The majority (93%) of the larvae in the musculature occurred in the hypaxial sections anterior to the anus. As A. simplex larvae commonly occur in the musculature of wild Atlantic salmon, consumption of unfrozen, raw or semi-raw musculature represents a risk for humans developing anisakiasis.

De novo assembly of Sockeye salmon kidney transcriptomes reveal a limited early response to piscine reovirus with or without infectious hematopoietic necrosis virus superinfection.

BACKGROUND: Piscine reovirus (PRV) has been associated with the serious disease known as Heart and Skeletal Muscle Inflammation (HSMI) in cultured Atlantic salmon Salmo salar in Norway. PRV is also prevalent in wild and farmed salmon without overt disease manifestations, suggesting multifactorial triggers or PRV variant-specific factors are required to initiate disease. In this study, we explore the head kidney transcriptome of Sockeye salmon Oncorhynchus nerka during early PRV infection to identify host responses in the absence of disease in hopes of elucidating mechanisms by which PRV may directly alter host functions and contribute to the development of a disease state. We further investigate the role of PRV as a coinfecting agent following superinfection with infectious hematopoietic necrosis virus (IHNV) - a highly pathogenic rhabdovirus endemic to the west coast of North America. RESULTS: Challenge of Sockeye salmon with PRV resulted in high quantities of viral transcripts to become present in the blood and kidney of infected fish without manifestations of disease. De novo transcriptome assembly of over 2.3 billion paired RNA-seq reads from the head kidneys of 36 fish identified more than 320,000 putative unigenes, of which less than 20 were suggested to be differentially expressed in response to PRV at either 2 or 3 weeks post challenge by DESeq2 and edgeR analysis. Of these, only one, Ependymin, was confirmed to be differentially expressed by qPCR in an expanded sample set. In contrast, IHNV induced substantial transcriptional changes (differential expression of > 20,000 unigenes) which included transcripts involved in antiviral and inflammatory response pathways. Prior infection with PRV had no significant effect on host responses to superinfecting IHNV, nor did host responses initiated by IHNV exposure influence increasing PRV loads. CONCLUSIONS: PRV does not substantially alter the head kidney transcriptome of Sockeye salmon during early (2 to 3 week) infection and dissemination in a period of significant increasing viral load, nor does the presence of PRV change the host transcriptional response to an IHNV superinfection. Further, concurrent infections of PRV and IHNV do not appear to significantly influence the infectivity or severity of IHNV associated disease, or conversely, PRV load.

Seatrout (Salmo trutta) is a natural host for Parvicapsula pseudobranchicola (Myxozoa, Myxosporea), an important pathogen of farmed Atlantic salmon (Salmo salar).

BACKGROUND: Parvicapsula pseudobranchicola (Myxozoa) causes widespread infections in farmed Atlantic salmon in northern Norway. Heavily infected salmon become runts, probably due to vision impairment or blindness. The salmon are likely infected by waterborne actinospores, released by an alternating annelid host, but the life cycle of P. pseudobranchicola is unknown. Seatrout and Arctic charr have been considered possible hosts for the parasite, but firm evidence has been lacking. FINDINGS: We show for the first time the presence of mature spores of P. pseudobranchicola in seatrout. The seatrout were infected with high intensities of P. pseudobranchicola in the pseudobranchs in early April. The presence of mature spores in early spring suggests that the fish had been infected late the previous year, a pattern of infection similar to that observed for farmed salmon stocked in autumn. Although heavily infected, the fish did not display any symptoms consistent with parvicapsulosis. The results suggest that the life cycle of P. pseudobranchicola is more adapted to seatrout, rather than to Atlantic salmon. CONCLUSIONS: The presence of mature spores of P. pseudobranchicola in seatrout confirms that seatrout is a natural host for this myxosporean and this is also the first record of these spores in the pseudobranch of a wild salmonid. Furthermore, wild trout from non-farming areas may become heavily infected with P. pseudobranchicola, developing pseudobranch pathology resembling that of farmed Atlantic salmon suffering from parvicapsulosis.

Mycobacterium salmoniphilum infection in burbot Lota lota.

Burbot Lota lota sampled from lakes Mjosa and Losna in southeastern Norway between 2005 and 2008 were found to be infected with Mycobacterium salmoniphilum at a culture-positive prevalence of 18.6 and 3.3%, respectively. The condition factor (CF) of mycobacteria-affected fish sampled from Mjøsa in 2008 was lower than the average CF of total sampled fish the same year. Externally visible pathological changes included skin ulceration, petechiae, exopthalmia and cataract. Internally, the infections were associated with capsulated, centrally necrotic granulomas, containing large numbers of acid-fast bacilli, found mainly in the mesenteries, spleen, heart and swim bladder. Mycobacterial isolates recovered on Middlebrook 7H10 agar were confirmed as M. salmoniphilum by phenotypical investigation and by partial sequencing of the 16S rRNA, rpoB and Hsp65genes as well as the internal transcribed spacer (ITS1) locus. This study adds burbot to the list of fish species susceptible to piscine mycobacteriosis and describes M. salmoniphilum infection in a non-salmonid fish for the first time.

Polyclonal hypergammaglobulinemia and autoantibody production induced by vaccination in farmed Atlantic salmon.

The introduction of oil-adjuvanted vaccines in salmon aquaculture made large-scale production feasible by reducing the impact of infections. Vaccines given intraperitoneally (ip) contain oil adjuvant such as mineral oil. However, in rodents, a single ip injection of adjuvant hydrocarbon oil induces lupus-like systemic autoimmune syndrome. We have recently reported that autoimmune disease in farmed salmon, characterized by production of various autoantibodies, immune complex glomerulonephritis, liver thrombosis, and spinal deformity, are previously unrecognized side effects of vaccination. In the present study, we examined whether vaccination-induced autoantibody production in farmed Atlantic salmon is a mere result of polyclonal B-cell activation. Sera were collected from 205 vaccinated and unvaccinated Atlantic salmon (experimental, 7 farms) and wild salmon. Total IgM levels and autoantibodies to salmon blood cell (SBC) extract in sera were measured by ELISA and the relationship between hypergammaglobulinemia and autoantibody production was analyzed. Comparison of endpoint titers vs levels/units using a single dilution of sera in detection of autoantibodies to SBC showed near perfect correlation, justifying the use of the latter for screening. Both total IgM and anti-SBC antibodies are increased in vaccinated salmon compared with unvaccinated controls, however, they do not always correlate well when compared between groups or between individuals, suggesting the involvement of antigen-specific mechanisms in the production of anti-SBC autoantibodies. The primary considerations of successful vaccine for aquaculture are cost-effectiveness and safety. Vaccination-induced autoimmunity in farmed Atlantic salmon may have consequences on future vaccine development and salmon farming strategy. Evaluation for polyclonal hypergamamglobulinemia and autoimmunity should be included as an important trait when vaccine efficacy and safety are evaluated in future.

Wild arctic char Salvelinus alpinus and trout Salmo trutta: hosts and reservoir of the salmonid pathogen Spironucleus salmonicida (Diplomonadida; Hexamitidae).

Spironucleus salmonicida is a diplomonad flagellate known to cause systemic infections in farmed salmonids. In northern Norway, outbreaks of spironucleosis in farmed Atlantic salmon Salmo salar have been a recurring problem. Common to all these outbreaks was the origin of smolts: all came from the same farm. In the present study, wild Arctic char Salvelinus alpinus and brown trout Salmo trutta were sampled from the lakes used as a water source for the smolt supplier. In addition, smolt and three-spined sticklebacks Gasterosteus aculeatus were sampled from the smolt farm. Bile and intestinal contents from the sampled fish were examined by light microscopy and PCR. Spironucleus salmonicida was identified in both wild Arctic char and brown trout from the lakes used as water sources by the smolt farm, suggesting that the farmed fish were exposed to this pathogen before transfer to the sea. Spironucleus barkhanus and Spironucleus salmonis were also identified in the sampled fish. The present study also demonstrated that infections with multiple Spironucleus species are present in wild salmonids. No indications of disease related to diplomonad infections were observed in the wild fish, suggesting that wild salmonids are reservoir hosts of Spironucleus salmonicida.

Vaccination-induced systemic autoimmunity in farmed Atlantic salmon.

Over half of the salmon consumed globally are farm-raised. The introduction of oil-adjuvanted vaccines into salmon aquaculture made large-scale production feasible by preventing infections. The vaccines that are given i.p. contain oil adjuvant such as mineral oil. However, in rodents, a single i.p. injection of adjuvant hydrocarbon oil induces lupus-like systemic autoimmune syndrome, characterized by autoantibodies, immune complex glomerulonephritis, and arthritis. In the present study, whether the farmed salmon that received oil-adjuvanted vaccine have autoimmune syndrome similar to adjuvant oil-injected rodents was examined. Sera and tissues were collected from vaccinated or unvaccinated Atlantic salmon (experimental, seven farms) and wild salmon. Autoantibodies (immunofluorescence, ELISA, and immunoprecipitation) and IgM levels (ELISA) in sera were measured. Kidneys and livers were examined for pathology. Autoantibodies were common in vaccinated fish vs unvaccinated controls and they reacted with salmon cells/Ags in addition to their reactivity with mammalian Ags. Diffuse nuclear/cytoplasmic staining was common in immunofluorescence but some had more specific patterns. Serum total IgM levels were also increased in vaccinated fish; however, the fold increase of autoantibodies was much more than that of total IgM. Sera from vaccinated fish immunoprecipitated ferritin and approximately 50% also reacted with other unique proteins. Thrombosis and granulomatous inflammation in liver, and immune-complex glomerulonephritis were common in vaccinated fish. Autoimmunity similar to the mouse model of adjuvant oil-induced lupus is common in vaccinated farmed Atlantic salmon. This may have a significant impact on production loss, disease of previously unknown etiology, and future strategies of vaccines and salmon farming.

Severe mortality in wild Atlantic salmon Salmo salar due to proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae (myxozoa).

Extensive mortality in Atlantic salmon fry was reported in the River Aelva from 2002 to 2004. Dead fish were collected in late summer 2006, and live fish were sampled by electrofishing in September the same year. At autopsy and in histological sections, the fish kidneys were found to be pale and considerably enlarged. Proliferative lesions with characteristic PKX cells were seen in a majority of the fish. DNA from kidney samples of diseased fish was subjected to PCR and sequencing, and the amplified sequences matched those of Tetracapsuloides bryosalmonae. We concluded that this myxozoan transmitted from bryozoans was the main cause of the observed mortality in salmon fry in 2006. Results from quantitative electrofishing in 2005 and 2006, combined with the observed fry mortality from 2002 to 2004, show that the smolt production in the river is severely reduced and that T. bryosalmonae is the most likely explanation for this decline. The present study is the first to report a considerable negative population effect in wild Atlantic salmon due to proliferative kidney disease (PKD). It also represents the northernmost PKD outbreak in wild fish. The river is regulated for hydroelectric power purposes, causing reduced water flow and elevated summer temperatures, and the present PKD outbreak may serve as an example of increased disease vulnerability of northern fish populations in a warmer climate.

First description of cardiomyopathy syndrome (CMS)-related lesions in wild Atlantic salmon Salmo salar in Norway.

This report represents the first diagnosis of cardiomyopathy syndrome (CMS) in migrating, wild Atlantic salmon Salmo salar from 1 major river and off the coast of Norway. Previously, this disease has been diagnosed only in farmed Atlantic salmon. The possible significance of the disease in wild stocks of salmon is discussed.

Heart morphology in wild and farmed Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss.

The normal shape of the salmonid ventricle is a triangular pyramid with the apex pointing caudoventrally. A strong positive correlation has been established between this shape and optimum cardiac output and function. Domesticated salmonids appear to have developed a more rounded ventricle with misaligned bulbus arteriosus. Several reports from fish health veterinarians indicate that fish with abnormal heart morphology have a high mortality rate during stress-inducing situations like grading, transportation and bath treatments. The present paper compares and describes the ventricle morphology of wild vs. farmed Atlantic salmon, and wild steelhead (anadromous rainbow trout) vs. farmed rainbow trout. Several parameters were measured to provide numerical measurement of the differences in shape, i.e. height:width ratio and the angle between the longitudinal ventricular axis and the axis of the bulbus arteriosus. We conclude that the hearts of farmed fish are rounder than those in corresponding wild fish, and that the angle between the ventricular axis and the axis of the bulbus arteriosus is more acute in wild fish than in their farmed counterparts. Further studies are necessary to reveal the prevalence, functional significance and possible causes of these abnormal hearts.

Cardiac abnormality with associated hernia in farmed rainbow trout Oncorhynchus mykiss.

A new type of cardiac malformation in rainbow trout Oncorhynchus mykiss from a broodstock fish farm is described. The ventricle of affected fish was located dorsodextrally to the atrium, while the latter was saccular, grossly enlarged and protruded through the muscles of the ventral body wall, forming a hernia covered only by dermis and epidermis. Histopathological changes included hypoplasia of the outer compact layer of the ventricular myocardium and severe distension of trabecular structures within the ventricle and atrium. Affected fish tolerated stress very poorly, and the majority of the affected fish died during the freshwater period. The causation(s) are not known, but hereditary and environmental factors are likely, as no infectious agents were isolated or detected microscopically.