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     

Multiple central-place territories in wild young-of-the-year Atlantic salmon Salmo salar

1. The space use of central-place foragers, animals that forage from and return to a single central place such as a nest, burrow or sleeping site, is well documented. Limited data, however, exist for multiple central-place foragers that alternate among several central places. 2. The conventional view of stream-dwelling salmonids suggests that they conform to the central-place territorial model (CPTM) by (i) attacking prey and intruders from one primary foraging station, and defending (ii) small (iii) exclusive areas that (iv) increase with body size. 3. Recent studies suggest greater variability in salmonid space-use than would be expected by the CPTM, but tend to focus on the time allocated towards different activities rather than their distribution in space, especially for young-of-the-year (YOY) fish that are hard to tag and monitor in the wild. 4. In this study, the validity of CPTM was tested by mapping the daily space use of 50 YOY Atlantic salmon in a natural stream via repeated observations of tagged fish in diverse habitats, and by comparing these to earlier estimates of territory use in YOY salmonids. 5. The 50 YOY Atlantic salmon were multiple central-place foragers. All fish visited more than one foraging station (median = 12.5 stations), visited most stations (68.5%) repeatedly, showed limited fidelity to a particular station and typically attacked prey only while holding a position at a station. 6. The multiple central-place territories of the 50 fish were large (mean = 0.932 m(2)) compared to earlier territory size estimates (mean = 0.107 m(2)) for salmonids of similar size and, surprisingly, did not increase with body size. Focal fish attacked intruders from similar distances as reported earlier for much smaller territories, suggesting that large territories are less exclusively defended at any given time. 7. Overall, this study provides a new view on foraging and territoriality in stream salmonids, and on the small but diverse literature on multiple central-place foragers. Further studies, however, are needed to clarify the evolutionary benefits and population consequences of multiple central-place space-use in mobile animals.     

Migratory behaviour of wild and farmed Atlantic salmon (Salmo salar) during spawning

Migratory behaviour at spawning of wild and newly-escaped farmed Atlantic salmon was analysed by radio telemetry in the River Alta, North Norway. Spawning areas were located by aerial surveys. Farmed females moved significantly more than wild females ( P <0.01). There was no such difference between the two groups of males. About 83% of the wild fish stayed within identified spawning areas for 1 day or longer. The corresponding figure for farmed salmon was only 43% ( P <0.05). Wild salmon stayed 8.1 days inside spawning areas and farmed salmon 5.2 days. The present results suggest that escaped farmed salmon had reduced spawning success compared with wild fish.     

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.     

Morphologic description of infectious salmon anaemia virus (ISAV)-induced lesions in rainbow trout Oncorhynchus mykiss compared to Atlantic salmon Salmo salar

In the present study the pathogenesis of experimental infectious salmon anaemia virus (ISAV) infection in rainbow trout Oncorhynchus mykiss (Walbaum, 1972) and Atlantic salmon Salmo salar was compared. The virus infection in the 2 species demonstrated different mortality patterns and pathology characteristics. Atlantic salmon showed a typical acute mortality pattern peaking at 8 to 16 d post-infection (dpi) depending on virus dose, whereas in rainbow trout, only the highest virus dose (10(7.13-7.8) TCID50/200 microl) showed a similar pattern. The middle (10(4.13) TCID50/200 microl) and lowest virus doses (10(2.13) TCID50/200 microl) in rainbow trout induced only sporadic protracted mortality, lasting up to 46 dpi. Infected rainbow trout that were live-sampled and those that died demonstrated increased erythrophagia, clusters of cellular degeneration in the haematopoietic portion of the kidney, and occasionally epicarditis, endocarditis and myocarditis. These lesions are very different from the typical necrosis in liver and kidney that occur in infected Atlantic salmon, and some of them may be indicative of an antiviral response by a resistant host to the ISAV infection. Virus was detected in the endothelium of the rainbow trout tissues using in situ hybridization, supporting our conclusions of the ISAV-induced lesions in this report.     

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.     

First feeding of Atlantic salmon (Salmo salar L.) under different photoperiods

Juvenile Atlantic salmon ( Salmo salar L. ) were first fed under four different static photoperiods (LD 24:0, LD 21:3, LD 18:6, LD 12:12) in two experiments. Under LD 24:0, continuous feeding or feeding 12 hours per day did not affect growth rate. In both experiments the roup on continuous light (LD 24:0) had highest growth rate. Growth was reduced on reduced dayfength. It is suggested that the difference in growth between long day (LD 21:3) and continuous light (LD 24:0) was caused by a growth inhibition during the dark period.

Zusammenfasung

Erste Nahrung des Atlantischen Lachses (Salmo salar L .)
Jungfische des atlantischen Lachses ( Salmo ralar L. ) wurden unter vier verschiedenen Photoperioden in zwei Experimenten erstmals gefüttert (LD 24:0; LD 21:3; LD 18:6; LD 12:12). Bei kontinuierlicher Fütterung (LD 24:0) oder Fütterung über 12 Stunden pro Tag, war die Wachsturnsrate nicht beeinflußt. In beiden Exerimenten hatte die Gruppe, die unter durchgehender Beleuchtung aufgezogen wurde, die höchste Wacgstumsrate. Das Wachsturn war bei kürzerer Tageslänge reduziert. Aus den Daten wird geschlossen, daß die Differenz im Wachstum zwischen dem Langtag (LD 21:3) und der durchgehenden Beleuchtung (LD 24:0) durch eine Wachtumshemmung während der Dunkelzeit verursacht wurde.     

Ecological model of interactions between escaped and wild Atlantic salmon Salmo salar

Atlantic salmon in Maine were once abundant but have become depleted, and are listed as endangered under the federal Endangered Species Act. Historically, salmon numbers in Maine may have been as high as 100 000 adults, but habitat loss, pollution and overfishing have contributed to the decline of the species. In 2000, only 110 adults returned to spawn in Maine rivers. Maine produces c. 15 000 metric tons/year of aquacultured Atlantic salmon from a total of nearly 600 coastal net pens. Escapees from these pens may interact with the wild salmon. The dynamics of salmon populations under such conditions are poorly understood. In order to illuminate the role aquaculture may play in such a system, we have developed a model for simulating population trajectories for both wild salmon and competing populations derived from aquaculture escapes. The model simulates a small population of wild salmon based in a stream/estuary system, into which an aquaculture facility is losing fish to escapes. Biological parameters in the model were estimated as much as possible from data in the USFWS report on Maine salmon. We used the model to investigate the consequences of a variety of ecological interactions between the wild and cultured fish including competitive, genetic and disease effects. Initial results indicate that many of these effects allow the aquaculture‐derived population to supplant the wild fish, but that wild populations may still persist under some conditions.     

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.     

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'.     

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.     

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.     

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.     

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.     

Cloning of the Atlantic salmon (Salmo salar) estrogen receptor-alpha gene

A cDNA clone encoding most of an Atlantic salmon (Salmo salar) estrogen receptor (ER) was obtained from a liver cDNA library and the remainder of the coding sequence from the gene was isolated from a genomic library. Sequence comparisons showed that the cloned gene represents ER-alpha. Expression of the ER-alpha gene in male and female salmon parr was analysed by RT-PCR. Highest expression was found in brain and liver, with lower levels of ER-alpha mRNA present in all other tissues tested. There was little difference in expression of ER-alpha between male and female.     

Nucleotide sequence variation in isolates of infectious salmon anaemia virus (ISAV) from Atlantic salmon Salmo salar in Scotland and Norway

The nucleotide sequences of segments 2 and 8 of infectious salmon anaemia virus (ISAV) isolates from Scotland and Norway were determined and compared. Sequence variations were found in both segments, with segment 2 being more variable. These variations were of the same degree as those found in previous comparisons of the first recorded strain of ISAV in Scotland and Norwegian strains for which sequence information was available. The sequences again demonstrate the separation of European and Canadian strains of ISAV but, as is expected for an RNA virus, reveal that the European ISAV is not homogeneous. These results demonstrate the value of nucleotide sequences as a tool for strain identification and epidemiological investigation of ISAV.     

Organisation of the mitochondrial genome from Atlantic salmon (Salmo salar)

A restriction map of Atlantic salmon mitochondrial DNA was constructed. The smallest XbaI fragment of the salmon mitochondrial genome was cloned and subjected to partial DNA sequence analysis. This fragment contains the genes for ATPase 6 and cytochrome oxidase III. The putative organisation of the mitochondrial genome relative to the physical map is shown.     

Biliverdin reductase from the liver of Atlantic salmon (Salmo salar)

Biliverdin reductase was characterized and purified from the liver of Atlantic salmon (Salmo salar) using a novel enzymatic staining method. The properties of the enzyme are quite different from those of mammals. The purified enzyme is a monomeric protein with a molecular weight of approximately 68 kD and an isoelectric point of around 3.8. The enzyme can utilize both NADH and NADPH as coenzyme, but the kinetic properties of the NADH-dependent and the NADPH-dependent enzyme activities are different: K _m value for biliverdin IX is 0.6 M in the NADPH system, while it is 6.8 M in the NADH system. Both enzyme activities are inhibited by excess biliverdin IX, but the NADPH-dependent enzyme activity is far more susceptible. The optimum pH for activity is 5.5 with NADPH and 6.0 with NADH. The optimum reaction temperature is 35°C.