Tenacibaculum sp. associated with winter ulcers in sea-reared Atlantic salmon Salmo salar

Coldwater-associated ulcers, i.e. winter ulcers, in seawater-reared Atlantic salmon Salmo salar L. have been reported in Norway since the late 1980s, and Moritella viscosa has been established as an important factor in the pathogenesis of this condition. As routine histopathological examination of winter ulcer cases in our laboratory revealed frequent presence in ulcers of long, slender rods clearly different from M. viscosa, a closer study focusing on these bacteria was conducted. Field cases of winter ulcers during 2 sampling periods, 1996 and 2004-2005, were investigated and long, slender rods were observed by histopathological examination in 70 and 62.5% of the ulcers examined, respectively, whereas cultivation on marine agar resulted in the isolation of yellow-pigmented colonies with long rods from 3 and 13% of the ulcers only. The isolates could be separated into 2 groups, both identified as belonging to the genus Tenacibaculum based on phenotypic characterization and 16S rRNA sequencing. Bath challenge for 7 h confirmed the ability of Group 1 bacterium to produce skin and cornea ulcers. In fish already suffering from M. viscosa-induced ulcers, co-infection with the Group 1 bacterium was established within 1 h. Ulcers from field cases of winter ulcers and from the transmission experiments tested positive by immunohistochemistry with polyclonal antiserum against the Group 1 bacterium but not the Group 2 bacterium. Our results strongly indicate the importance of the Group 1 bacterium in the pathogenesis of winter ulcers in Norway. The bacterium is difficult to isolate and is therefore likely to be underdiagnosed based on cultivation only.     

Mortality in Atlantic salmon (Salmo salar) associated with trichodinid ciliates

A protozoan infection (Trichodina truttae) was identified in captive Atlantic salmon (Salmo salar) kelts that died in spring of 1988 and 1989. Fish with intense infections showed signs of listlessness, erratic swimming and inappetence. The infection induced excessive mucus secretion, epithelial sloughing and lesions that probably permitted entry of opportunistic bacteria which eventually caused ulcers and death. A seawater bath for 30 min each week for 4 wk effectively controlled the parasite.     

Parvicapsula pseudobranchicola (Myxosporea) in farmed Atlantic salmon Salmo salar. Tissue distribution, diagnosis and phylogeny

Parvicapsula pseudobranchicola infections in farmed Atlantic salmon in Norway are associated with low-grade to significant mortalities. The parasite is found as mature spores in pseudobranchs, but has also been detected in the gills, liver and kidney. Diagnosis has relied on the detection of Parvicapsula spores, with the pseudobranch being the preferred organ. A better understanding of the epizootiology of this myxosporean is a prerequisite for appropriate management and control. Hence, early detection of infections and life cycle studies are needed. We sequenced the small subunit (ssu) rDNA (18S) from P. pseudobranchicola and developed a sensitive diagnostic PCR protocol. This allowed us to (1) identify appropriate tissues for diagnostic assays, (2) examine the intraspecific variation in ssu rDNA in the parasite's Norwegian range, (3) examine annelid potential primary hosts and (4) obtain additional ssu rDNA sequences of marine Parvicapsula species to perform a phylogenetic study. Primers were constructed targeting the ssu rDNA from P. minibicornis. With these we obtained a partial ssu sequence of the P. pseudobranchicola type isolate. A new set of primers (PCF3/PCR3) was constructed for diagnostic purposes. These were tested against DNA from the host and several myxozoan species infecting Norwegian salmon. The primers give a positive product of 203 bp and pick out P. pseudobranchicola in salmnonids. They also amplify the congeners P. unicornis and P. asymmetrica infecting unrelated fish. The PCR protocol developed showed a greater sensitivity than light microscopy. The pseudobranchs were always positive and are the recommended organ for PCR diagnostics. There was no sequence variation between geographic isolates from farmed salmon. Preliminary examinations of marine polychaetes and oligochaetes collected from farm sites with parvicapsulose problems were negative. A comparison of the sequence of the ssu rDNA from P. pseudobranchicola with that of other myxozoans shows that it groups closely together with P. unicornis and P. asymmetrica. The closest relative to this group is P. minibicornis.     

Transport-associated proteins in Atlantic salmon (Salmo salar)

 The major histocompatibility complex (Mhc) regions of mice, rats, and humans all contain a pair of related genes, TAP1 and TAP2, which encode members of a large superfamily of proteins of similar structure and function. A functional TAP1/TAP2 heterodimer is probably required for efficient presentation of antigens to CD8⁺ T cells. This heterodimer resides in the membrane of the endoplasmic reticulum, and transports peptides from the cytoplasm into the endoplasmic reticulum lumen for binding to Mhc class I molecules. The TAP transporter demonstrates specificity for both peptide sequence and length, and in rats, allelic variation in the sequence of the transporter molecules results in differential ability to transport particular peptides. Here we report two expressed Sasa-TAP2 loci, both of which are polymorphic, as well as an expressed Sasa-TAP1 locus from Atlantic salmon. The Sasa-TAP2A locus has a genomic organization similar to the human TAP2 equivalent. Received: 23 December 1996 / Revised: 26 February 1997     

A lymphosarcoma in an Atlantic salmon (Salmo salar)

A lymphosarcoma that appeared to be of thymic origin and of lymphoblastic type was found in a 3.5-yr-old Atlantic salmon (Salmo salar). The fish was from a population of 60 broodfish maintained at a research fish laboratory. A large tumor mass was found under the left operculum. Small tumor nodules were found on the swim bladder and in the abdominal adipose tissue. The location of this neoplasm differed from those of previously described tumors in this fish species.     

Liver ultrastructure of juvenile Atlantic salmon (Salmo salar)

Light and transmission electron microscopy of the liver of juvenile Atlantic salmon (Salmo salar) reveals a tubular arrangement of parenchymal cells, with biliary passages typically located at the center of tubules. Hepatocytes generally contain a single nucleus surrounded by a cuff of rough endoplasmic reticulum (RER), with many round to elongate mitochondria associated with the perinuclear RER. Whereas glycogen deposits are common and usually lie at the cell periphery, parenchymal cells seldom contain lipid droplets. Golgi complexes and heterogeneous dense bodies also occur in many hepatocytes, often in close proximity to bile canaliculi. Numerous microvilli from hepatocytes extend into the subendothelial space of Disse, which is also the location of stellate fat-storing cells. Interhepatocytic macrophages, sometimes containing prominent phagolysosomes and residual bodies, are common in the liver. The intrahepatic biliary system consists of intercellular canaliculi, bile pre-ductules, ductules, and ducts. In contrast to some other teleosts, the liver of the Atlantic salmon contains no intracellular bile canaliculi or Kupffer cells. The hepatic endothelium, arterioles, and perivenous regions are also described.     

Cloning of the Atlantic salmon (Salmo salar) IL-1 receptor associated protein

In mammals, the pro-inflammatory cytokine interleukin-1 signals through a receptor complex containing a type I interleukin-1 receptor (IL-1RI) and a receptor associated protein (IL-1RAcP). Previously, we have described a cDNA from Atlantic salmon encoding a molecule with homology to the mammalian IL-RI. This molecule was named IL-1 receptor like protein (IL-1RLP) in the absence of functional data to support its proposed role as the salmon IL-1RI. Here, we describe the cloning and characterisation of a cDNA encoding salmon IL-1RAcP. Like other members of the IL-1R family, the salmon IL-1RAcP encodes three extracellular immunoglobulin-like domains and a cytoplasmic Toll/Interleukin-1 receptor (TIR) domain involved in signalling. Specific binding of salmon IL-1RAcP to IL-1RLP was shown by co-immunoprecipitation studies.     

Upstream migration of adult Atlantic salmon, Salmo salar L., in the River Vefsna, northern Norway

Daily ascents of adult Atlantic salmon ( Salmo salar ) in the Laksforsen waterfall in the River Vefsna were recorded over 3 years. Ascent was correlated to 12 physical and meteorological parameters by multiple regression analysis. Change in water temperature was included in the regression model in all 3 years, and change in river flow was also included in 2 of the 3 years. No other variable was included in the regression model at the 0.05 significance level.     

A microsatellite linkage map for Atlantic salmon (Salmo salar)

A linkage map of the Atlantic salmon is described here consisting of 15 linkage groups containing 50 microsatellite loci with a 14 additional unlinked markers (including three allozymes). The map shows the largest sex-specific recombination rate differences so far found in any vertebrate species (3.92:1 female:male). Homologies with previous linkage mapping studies of Atlantic salmon and rainbow trout are described. An in silico search of the Genbank database carried out using the microsatellites used in the mapping process identified significant matches between the flanking regions of the microsatellite SS11 and the calcium-binding mitochondrial carrier protein, 'Aralar1'.     

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.     

Gyrodactyloides bychowskii (Monogenea: Gyrodactylidae) from sea-caged Atlantic salmon Salmo salar in Scotland: occurrence and ribosomal RNA sequence analysis

Gyrodactyloides bychowskii has been recorded in Scottish waters for the first time. The parasite was found on the gills of Atlantic salmon reared in seawater. An integrated morphological and molecular examination of the parasite was carried out. Prevalence of the parasite was greatest in February and declined to 0 by June in 1999. During 2000, parasites were located in March and November. An overdispersion of parasites was recorded, with intensity of infection reaching over 200 parasites per gill arch in some fish. Parasitised gill tissue showed hyperplasia and hypertrophy but not always at the site of parasite attachment. The internal transcribed spacer of the ribosomal RNA gene array was amplified by PCR and sequenced. This sequence shared greatest similarity with the internal transcribed spacer of Gyrdicotylus gallieni, followed by Gyrodactylus species. This is the first molecular analysis of this parasite and provides sequence data that may be used in comparison of G. bychowskii from other locations or in phylogenetic analysis of this group of Monogenea.     

Infestations by Gyrodactylus sp. of Atlantic salmon, Salmo salar L., in Norwegian rivers

Young Atlantic salmon, Salmo salar , brown trout, Salmo trutta , and Arctic char, Salvelinus alpinus , from eight rivers in North and Mid Norway were examined for Gyrodactylus. The fish were collected from 1975 to 1980. A Gyrodactylus salaris type was observed infecting salmon from six of these rivers. No trout or char were infected. A high frequency and intensity of infection of salmon were observed in all but one of the rivers surveyed. In the Saltdalselva, only one specimen of Gyrodactylus infecting one fish was observed. No subsequent mortality of salmon was observed in this river while there were signs of a high mortality of salmon in the other rivers. The salmon parr were more frequently attacked than the fry, the mortality of salmon seemed to have happened in most of the rivers one year after the first observations of Gyrodactylus were made. The mortality of salmon and the high infection rate of Gyrodactylus in these rivers appears unique, and as far as known to the authors there are no other described cases of mortality due to Gyodactylus in Atlantic salmon in natural waters. The reasons for the outbreak of Gyrodactylus in these rivers are not known. Two theories are discussed: one that the fish were weakened by environmental factors and the other that Gyrodactylus was introduced from some of the infected salmon hatcheries in Scandinavia.     

Purification and characterization of Atlantic salmon (Salmo salar) fibrinogen

This study describes a purification protocol of salmon fibrinogen that gives a consumable and highly clottable fibrinogen. Some characteristics of salmon and human fibrinogen are compared. Fibrinogen was purified from barium sulphate adsorbed plasma of Atlantic salmon, using two steps of 25% ammonium sulphate precipitation followed by ultrafiltration. The clottability of the purified salmon fibrinogen was 91%. The Aalpha chains of salmon fibrinogen were heterogeneous with a molecular mass of 90-110 kDa, compared to approximately 67 kDa of human fibrinogen Aalpha chains. The Bbeta and gamma chains of salmon and human fibrinogen had molecular masses of approximately 55 and 50 kDa, respectively. Western blotting revealed that polyclonal rabbit anti-human fibrinogen antibodies had affinity for the gamma chains of salmon fibrinogen, making it possible to study factor XIII activity in purified salmon fibrinogen. Cross-linking of either gamma-gamma or gamma-alpha chains was not detected upon incubation of the purified fibrinogen with thrombin and calcium alone, but was detected when clotting was performed in plasma indicating absence of factor XIII activity in the purified product.     

Swimbladder Leiomyosarcoma in Atlantic salmon (Salmo salar) in North America

Leiomyosarcoma with associated retrovirus were found in North America for the first time in adult Atlantic salmon (Salmo salar) held in a quarantine facility at the North Attleboro National Fish Hatchery (NANFH), Massachusetts, USA. The fish had been collected as age 1-2 yr animals from the Pleasant River, Maine, and were to be used as brood stock in a population augmentation program for that river. Neoplastic disease was observed at NANFH initially in older (age 4 yr) fish, followed by age 3 yr fish. Disease was not observed in age 2 yr fish. The mortality pattern was chronic.     

Catabolism of circulating collagen in the Atlantic salmon (Salmo salar)

The catabolic fate of circulating collagen (Col) in the Atlantic salmon (Salmo salar) was studied. Serum t_1/2 and organ distribution of circulating Col in salmon were determined using Col conjugated with ^l25I-tyramine cellobiose (¹²⁵I-TC), a low molecular weight adduct which is trapped intralysosomally at the site of uptake. Intravenously administered ^l25I-tyramine cellobioselabelled Col type I was prepared either from salmon skin (sCol) or rat skin (rCol). Biphasic clearance kinetics of ^l25I-TC-sCol in salmon were apparent, with 78% being removed from the circulation in an initial rapid α-phase (t_1/2(α) = 2.4 min), and 22% being removed more slowly in a terminalβ-phase (t]2(β) = 25.8 min). Serum half life of ¹²⁵I-TC-rCol was found to be 5.4 min (in this type of experiment the number of data points allow the determination of only a monophasic decay slope). Approximately 90% of recovered radioactivity was found in the kidney of the fish. In comparative experiments, 74% of administered ¹²⁵I-TC-sCol was cleared from the circulation of rats during an initial rapid α-phase with t_l/2(α) = 0.8 min, and 26% was eliminated in the terminal β-phase with t_1/2(β) = 7.2 min ^l25I-sCol was endocytosed and degraded in pure cultures of ral liver endothelial cells, which are the main site of clearance of circulating Col in the rat. Moreover, Col from the two species competed for the same receptor on cultured rat liver endothelial cells, Intravenous administration of tetramethyl rhodamine isothiocyanate-labelled sCol (TRITC-sCol) in salmon, and subsequent examination of sections of kidney in the fluorescence microscope, revealed that the fluorochrome was accumulated exclusively in discrete vesicles of sinusoidal lining cells. Analyses of kidney tissue 24h after intravenous administration of a mixture of fluorescein isothiocyanate-labelled latex beads and TRITC-sCol revealed no codistribution of the two fluorochromes, suggesting that the injected Col was taken up in cells different from macrophages. Purified pronephros macrophages prepared after simultaneous injections of stained beads and Col contained only fluorescein-labelled latex particles. Interestingly, the cells which had accumulated TRITC-sCol appeared to be equally distributed in both pronephros and the part of the kidney containing tubuli. We conclude that Col which gains access to the circulation of the Atlantic salmon is cleared mainly by uptake into sinusoidal lining cells of the kidney. These cells are distinct from phagocytosing macrophages, and morphologically similar to the highly specialized scavenging endothelial cells of mammalian liver sinusoids.     

Replication banding patterns in Atlantic salmon (Salmo salar).

Replication banding patterns have been obtained from in vivo treatment of Salmo salar using a modification of the 5-BrdU technique and in kidney cultures using the FPG staining method. Most of the chromosome pairs were identified in the karyotype based on the banding pattern, chromosome size, and centromere position. C-banding and replication banding patterns were compared.     

Periodicity in Atlantic salmon Salmo salar L. smolt migration

Behavioural and physiological mechanisms postulated for the control of downstream migration of Atlantic salmon smolts are reviewed briefly, and some new evidence is presented for their refusal to undergo sustained swimming. Although these mechanisms imply passive displacement as the primary means of emigration, it is likely that active components must also exist as the rates of travel of smolts through loch systems are only slightly slower than those recorded for river systems. The timing of these movements within 24 h periods is reviewed and it is shown that the predominantly nocturnal emigration pattern is evident on occasions in alevin, fry and parr stages also. Thus at migration the diel periodicity probably represents a seasonal locomotor rhythm which, under changed behavioural and physiological circumstances, results in downstream displacement.     

Diseases of farmed Atlantic salmon Salmo salar associated with infections by the microsporidian Paranucleospora theridion

The microsporidian Paranucleospora theridion was discovered in Atlantic salmon Salmo salar suffering from proliferative gill disease in a marine farm in western Norway in 2008. The parasite develops in cells of the reticuloendothelial system, cells important for normal immune function. The aim of this study was to see if P. theridion could play a part in some of the diseases with unclear causes in salmon production in Norway, i.e. proliferative gill disease (PGI), pancreas disease (PD), heart and skeletal muscle inflammation (HSMI) and cardiomyopathy syndrome (CMS). P. theridion was present in all areas with salmon farming in Norway, but high prevalence and densities of the parasite in salmon and salmon lice were only seen in southern Norway. This region is also the main area for PGI and PD in Norway. Quantification of pathogens associated with PGI, PD, HSMI and CMS diagnoses showed that P. theridion levels are high in southern Norway, and may therefore play a role in susceptibility and disease development. However, among the different diagnoses, fish with PGI are particularly heavily infected with P. theridion. Therefore, P. theridion appears as a possible primary agent in cases with high mortality in connection with PGI in western Norway.