Lymphocytopenia and the overwinter survival of Atlantic salmon parr, Salmo salar L.

The overwinter mortality rate of underyearling S2 Atlantic salmon parr (fish that will remain in fresh water for at least two years prior to smoltification) was almost ten times greater than that of S1 parr (fish that will smoltify after 1 year in fresh water) kept under similar conditions. The loss of condition ( K factor) of the S2 parr was proportionally greater than that of S1 parr during the early winter months and this coincided with a marked lymphocytopenia and thrombocytopenia in the S2 parr. Limited evidence indicates that S2 parr have chronically elevated blood cortisol levels during the winter months. It is suggested that chronic stress resulting (in part) from nutritional deficiency has a debilitating effect on the defence systems of these fish. The ultimate cause of mortality in most cases was bacterial fin-rot and/or fungal ( Saprolegnia ) infection. These findings are discussed in relation to the habitat requirements of overwintering salmonid fish.     

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'.     

Energetics in Atlantic salmon (Salmo salar L.) parr fed elevated dietary cadmium

Atlantic salmon (Salmo salar L.) parr were reared for 4 months on experimental diets supplemented with Cd (0.5, 5, 25, 125, or 250 mg Cd x kg(-1)) to assess the long-term energetic changes based on the digestibility and biochemical deposition of the major dietary nutrients and to evaluate a maximum tolerable dietary toxicant concentration. Growth did not differ significantly (P>0.05) from the control groups. The biochemical composition of the carcass, but not the viscera, was negatively affected by dietary Cd exposure. The significant decreases in protein, lipid, and glycogen concentrations in the carcass (P<0.05, 25 mg x kg(-1) compared to control groups) caused a reduction in calculated whole-body energy content in fish fed 125 mg x kg(-1)compared to control groups. This reduction in calculated whole-body energy content was explained by a concurrent significant disturbance to the gastrointestinal function (measured as reduced digestibility). Only at the highest dietary Cd exposure (250 mg x kg(-1)), increased metabolic costs to cope with Cd toxicity was thought to contribute significantly to the reduction in carcass energy content. The most important factor effecting calculated total energetics was nutrient digestibility. Based on the logarithmic effective median concentration for reduced calculated energy digestibility (dietary Cd concentration corresponding to 50% reduction, EC50), the maximum tolerable dietary Cd concentration is 11 mg x kg(-1) diet.     

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.     

Growth-rate and smolting-rate of progeny of male Atlantic salmon parr, Salmo salar L.

In experiments conducted in two successive years, the progeny of male Atlantic salmon parr ( Salmo salar L.) were found to grow in length at the same rate as the progeny of sea-run males. The proportions of these populations which smolted at one year old did not differ in the first experiment, but were significantly higher among progeny of parr (33%) than among progeny of sea run-adults (21%) in the second year. Survivals throughout the experiments were high, at 89 and 91% respectively in the two years. A possible inhibitory relationship between smolting and sexual reproduction in the same year is discussed.     

Farmed Atlantic salmon Salmo salar L. parr may reduce early survival of wild fish

The study examined the density‐mediated effects on growth, survival and dispersal of wild and farmed Atlantic salmon Salmo salar offspring in the period immediately following emergence, using a substitutive design. In small confined stream channels, wild parr coexisting with farmed parr had a significantly poorer survival, than wild parr alone. Density did not affect this relationship. In larger unconfined stream channels, wild parr coexisting with farmed parr entered a downstream trap in higher numbers than wild parr in allopatry. The results suggests that during the earliest life stages, farmed S. salar can outcompete wild S. salar, resulting in a reduced survival of wild S. salar.     

Inclusion of water temperature in a fuzzy logic Atlantic salmon (Salmo salar) parr habitat model

As water temperature is projected to increase in the next decades and its rise is clearly identified as a threat for cold water fish species, it is necessary to adapt and optimize the tools allowing to assess the quantity and quality of habitats with the inclusion of temperature. In this paper, a fuzzy logic habitat model was improved by adding water temperature as a key determinant of juvenile Atlantic salmon parr habitat quality. First, salmon experts were consulted to gather their knowledge of salmon parr habitat, then the model was validated with juvenile salmon electrofishing data collected on the Sainte-Marguerite, Matapedia and Petite-Cascapedia rivers (Québec, Canada). The model indicates that when thermal contrasts exist at a site, cooler temperature offered better quality of habitat. Our field data show that when offered the choice, salmon parr significantly preferred to avoid both cold areas (<15 °C) and warm areas (>20.5 °C). Because such thermal contrasts were not consistently present among the sites sampled, the model was only validated for less than 60% of the sites. The results nevertheless indicate a significant correlation between median Habitat Quality Index and parr density for the Sainte-Marguerite River (R² = 0.38). A less important, albeit significant (F-test; p = 0.036) relationship was observed for the Petite-Cascapedia river (R² = 0.14). In all instances, the four-variable (depth, velocity, substrate size and temperature) model provided a better explanation of parr density than a similar model excluding water temperature.     

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     

Sexual maturity increases mobility and heterogeneity in individual space use in Atlantic salmon (Salmo salar) parr

We assessed the effects of sexual maturity on space use in Atlantic salmon (Salmo salar) parr as facultative early maturation enables us to work on individuals belonging to the same cohort. We monitored the space use of 40 1-year-old males in natura throughout a breeding season. First, mature individuals covered longer distances (absolute and upstream) and located within broader home ranges than immature parr. Second, sexual maturity also generated a higher interindividual variability in space use. Finally, mature individuals exhibited a higher probability of association with likely breeding sites on average. However, some mature individuals experienced a lower probability than immature individuals, suggesting that the space use of some mature individuals may not be optimal. Moreover, mature parr exploiting a broader home range or covering longer upstream distances had a higher probability of association with likely breeding sites. Covering longer upstream distances may therefore increase the reproductive success of mature parr, while involving higher energetic costs and a greater risk of predation.     

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.     

Mating of anadromous Atlantic salmon, Salmo salar L., with mature male parr

Sexually mature male parr successfully mated with female anadromous Atlantic salmon, Salmo salar , in the absence of anadromous males. There was no significant difference between the proportion of eggs fertilized by mature male parr and anadromous males. One of the demographic consequences of our observations is that overfishing could eventually eliminate anadromy in male members of a population.     

Morphological differences in parr of Atlantic salmon Salmo salar from three regions in Norway

Morphological characters were compared in parr (total length 33-166 mm) of Atlantic salmon Salmo salar sampled from eight wild populations in three regions, three in northern, two in the middle and three in southern Norway, covering a distance of 1700 km (from 70° N to 58° N). On the basis of morphological characters 94·6% of the individuals were correctly classified into the three regions. Discrimination between populations within these three regions also had a high degree of correct classification (89·0-95·8%). Principle component analysis identified largest differences to be in head characters, notably eye diameter and jawbone, with the smallest diameter and head size among the northernmost populations. Fish from the southern rivers had a deeper body form whereas fish from the middle region had larger heads and pectoral fins. This illustrates that S. salar already in the early parr stage has morphological traits, which can be used in discrimination between regions and populations and that these differences are discernible in spite of the volume of escaped farmed fish spawning in Norwegian rivers during the past 30 years.     

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.     

Evidence for an autumn downstream migration of Atlantic salmon Salmo salar (Linnaeus) and brown trout Salmo trutta (Linnaeus) parr to the Baltic Sea

In the eastern Baltic rivers, anadromous salmonid parr are known to smoltify and migrate to the sea from March until June, depending on latitude, climate and hydrological conditions. In this study, we present the first records of autumn descent of brown trout Salmo trutta and Atlantic salmon Salmo salar from the Baltic Sea Basin. Otolith microchemistry analyses revealed that these individuals hatched in freshwater and had migrated to the brackish water shortly prior to capture. The fish were collected in 2006, 2008, 2009 and 2013 from Eru Bay (surface salinity 4.5–6.5 ‰), Gulf of Finland. This relatively wide temporal range of observations indicates that the autumn descent of anadromous salmonids is not a random event. These results imply that autumn descent needs more consideration in the context of the effective stock management, assessment and restoration of Baltic salmonid populations and their habitats.     

Pathogenesis and immune response in Atlantic salmon (Salmo salar L.) parr experimentally infected with salmon pancreas disease virus (SPDV)

Atlantic salmon parr were injected intraperitoneally with salmon pancreas disease virus (SPDV) grown on CHSE-214 cells. The viraemia, the histopathological changes in target organs and some immune parameters were taken at intervals up to 30 days post-infection (dpi). The earliest kind of lesion was necrosis of exocrine pancreas, appearing as soon as 2 dpi. It progressed towards complete tissue breakdown at 9 dpi before resolving gradually. Concurrent to this necrosis, a strong inflammatory response was in evidence from 9 dpi in the pancreatic area for a majority of fish. A necrosis of the myocardial cells of the ventricle occurred in infected fish mainly at 16 dpi and it faded thereafter. The monitoring of the plasma viral load showed a rapid haematogenous spreading of SPDV, peaking at 4 dpi, but also the absence of a secondary viraemia. No interferon (IFN) was detected following the infection of parr with SPDV, probably owing to an IFN activity in Atlantic salmon below the detection level of the technique. Neutralising antibodies against SPDV were in evidence from 16 dpi and they showed a time-related increasing titre and prevalence. The phagocytic activity in head-kidney leucocytes was always significantly higher in the infected fish than in the control fish, being particularly high by 9 dpi. Lysozyme and complement levels were both increased and they peaked significantly in the infected fish at 9 and 16 dpi respectively. These results demonstrated that an experimental infection of Atlantic salmon parr with SPDV provoked a stimulation of both specific and non-specific immunity with regards to the viraemia and the histopathology.     

Differential transferrin gene expression in Atlantic salmon (Salmo salar L.) freshwater parr and seawater smolts

The Atlantic salmon has a complex life-cycle in which it encounters a salinity barrier initially upon migration to the sea as a young smolt and later as an adult salmon returning to its natal river. Concurrent with seawater migration is a process termed smoltification which is a series of metabolic changes which transform the freshwater parr into smolts adapted for life in the marine environment. To gain an understanding of events occurring at the molecular level in the salmon liver during this developmental process, a cDNA library prepared from post-smolt salmon liver mRNA was screened with total liver cDNA probes synthesised from parr and smolts. Clones which hybridised more strongly to the smolt probe than the parr probe were chosen as candidates, for an analysis of liver gene expression implicated in seawater adaptation. Many of these cDNA clones encoded the iron binding protein transferrin. Transferrin mRNA levels were determined to be significantly higher in seawater smolt salmon than in freshwater smolts implying that transferrin may play a role in seawater adaptation.