Acid–base and respiratory effects of confinement in Atlantic salmon affected with amoebic gill disease

Amoebic gill disease (AGD) in cultured salmonids causes severe multifocal hyperplastic lesions in the gills with the potential to influence respiratory and acid–base physiology. Atlantic salmon Salmo salar affected with AGD were surgically implanted with dorsal aortic catheters and, following recovery, were confined for 5 min ( n  = 16) or left undisturbed ( n  = 8). Confinement caused an acute extracellular acidosis that was corrected in 6 h amongst surviving fish. There was a gradual increase in plasma lactate concentrations that peaked at 1 h post-confinement then declined by 9 h recovery. In a second experiment, AGD-affected fish were confined then recovered either in a tank of static water ( n  = 9) or while being forced to swim at 1·5 body lengths s⁻¹ ( n  = 6). There was no significant difference between fish recovered by swimming and those in static water in terms of recovery of the acute extracellular acidosis and lactate accumulations coincident with exhaustive exercise. Confinement severely compromised the survival of AGD-affected Atlantic salmon, although survivors appeared to recover similarly to other studies. Forced swimming of AGD-affected Atlantic salmon following confinement did not facilitate recovery and is unlikely to be a useful strategy for mitigating the effects of stressful episodes such as crowding and fish movement and commercial handling.     

Radio-transmitted electromyogram signals as indicators of physical activity in Atlantic salmon

Surgical methods developed to implant EMG (electromyogram) transmitters in Atlantic salmon Salmo salar were tested to calibrate electromyograms from axial red musculature to swimming speed in a swim speed chamber, and to compare electromyograms of fish from two stocks (Lone and Imsa). Ten Lone and eight Imsa salmon were equipped with internal EMG transmitters. Surgical procedures were acceptable, with 100% survival of all implanted fish during the study. It was possible to calibrate EMG pulse intervals to swimming speed in 14 of the 18 salmon run in the swim speed chamber ( r²= 0·35-0·76 for individuals, 0·63 for pooled data). Individuals differed in their EMG resting levels (EMGs recorded at 0·5 ms⁻¹), and so higher correlations were obtained between swimming speed and an activity index (EMG pulse intervals at different speeds/EMG resting levels) (pooled data, r² =0·75). The linear relationship between swimming speed and EMG pulse intervals differed significantly between the two stocks ( P <0·05). This successful calibration of EMGs to swimming speed opens the possibility of calibrating EMGs to oxygen consumption and the measurement of the metabolic costs of activity in field experiments.     

Adaptive trade-offs in juvenile salmonid metabolism associated with habitat partitioning between coho salmon and steelhead trout in coastal streams

1. Adaptive trade-offs are fundamental to the evolution of diversity and the coexistence of similar taxa and occur when complimentary combinations of traits maximize efficiency of resource exploitation or survival at different points on environmental gradients. 2. Standard metabolic rate (SMR) is a key physiological trait that reflects adaptations to baseline metabolic performance, whereas active metabolism reflects adaptations to variable metabolic output associated with performance related to foraging, predator avoidance, aggressive interactions or migratory movements. Benefits of high SMR and active metabolism may change along a resource (productivity) gradient, indicating that a trade-off exists among active metabolism, resting metabolism and energy intake. 3. We measured and compared SMR, maximal metabolic rate (MMR), aerobic scope (AS), swim performance (UCrit) and growth of juvenile hatchery and wild steelhead and coho salmon held on high- and low-food rations in order to better understand the potential significance of variation in SMR to growth, differentiation between species, and patterns of habitat use along a productivity gradient. 4. We found that differences in SMR, MMR, AS, swim performance and growth rate between steelhead trout and coho salmon were reduced in hatchery-reared fish compared with wild fish. Wild steelhead had a higher MMR, AS, swim performance and growth rate than wild coho, but adaptations between species do not appear to involve differences in SMR or to trade-off increased growth rate against lower swim performance, as commonly observed for high-growth strains. Instead, we hypothesize that wild steelhead may be trading off higher growth rate for lower food consumption efficiency, similar to strategies adopted by anadromous vs. resident brook trout and Atlantic salmon vs. brook trout. This highlights potential differences in food consumption and digestion strategies as cryptic adaptations ecologically differentiating salmonid species. 5. We hypothesize that divergent digestive strategies, which are common and well documented among terrestrial vertebrates, may be an important but overlooked aspect of adaptive strategies of juvenile salmonids, and fish in general.     

Behaviour during elevated water temperatures: can physiology explain movement of juvenile Atlantic salmon to cool water?

1. Temperature governs most physiological processes in animals. Ectotherms behaviourally thermoregulate by selecting habitats with temperatures regulating their body temperature for optimal physiological functioning. However, ectotherms can experience temperature extremes forcing the organisms to seek temperature refuge. 2. Fish actively avoid potentially lethal temperatures by moving to cool-water sites created by inflowing tributaries and groundwater seeps. Juvenile Atlantic salmon (Salmo salar) of different age classes exhibit different behavioural responses to elevated temperatures (>23 °C). Yearling (1+) and 2-year-old (2+) Atlantic salmon often cease feeding, abandon territorial behaviour and swim continuously in aggregations in cool-water sites; whereas young-of-the-year (0+) fish continue defending territories and foraging. 3. This study determined whether the behavioural shift in older individuals (2+) occurred when basal metabolic rate, driven by increasing water temperature, reached the maximum metabolic rate such that anaerobic pathways were recruited to provide energy to support vital processes. Behaviour (feeding and stress responses), oxygen consumption, muscle lactate and glycogen, and circulating blood lactate and glucose concentrations were measured in wild 0+ and 2+ Atlantic salmon acclimated to water temperatures between 16 and 28 °C. 4. Results indicate that oxygen consumption of the 2+ fish increased with temperature and reached a plateau at 24 °C, a temperature that corresponded to cessation of feeding and a significant increase in muscle and blood lactate levels. By contrast, oxygen consumption in 0+ fish did not reach a plateau, feeding continued and muscle lactate did not increase, even at the highest temperatures tested (28 °C). 5. To conclude, the experiment demonstrated that the 0+ and 2+ fish had different physiological responses to the elevated water temperatures. The results suggest that wild 2+ Atlantic salmon employ behavioural responses (e.g. movement to cool-water sites) at elevated temperatures in an effort to mitigate physiological imbalances associated with an inability to support basal metabolism through aerobic metabolic processes.     

Effects of species, culture history, size and residency on relative competitive ability of salmonids

The relative competitive ability of juvenile farm and wild salmonids was investigated to provide insight into the potential effects of introduction of cultured salmon on wild Pacific salmonid ( Oncorhynchus ) species. Aquarium experiments involving equal contests ( i.e. size matched, simultaneously introduced individuals) indicated that two wild coho salmon Oncorhynchus kisutch populations were competitively equal to a farm coho salmon population. In equal contests between farm Atlantic salmon Salmo salar (Mowi strain) and these wild coho salmon populations or coastal cutthroat trout Oncorhynchus clarki clarki , Atlantic salmon were subordinate in all cases. When Atlantic salmon were given a residence advantage, however, they were competitively equal to both wild coho salmon populations, but remained subordinate to coastal cutthroat trout. When Atlantic salmon were given a 10–30% length advantage, they were competitively equal to one wild coho salmon population but remained subordinate to the other. In equal contests in semi-natural stream channels, both wild coho and farm Atlantic salmon grew significantly more in the presence of the other species than when alone. It appears that coho salmon obtain additional food ration by out competing Atlantic salmon, whereas Atlantic salmon were stimulated to feed more in the presence of coho salmon competitors. These results suggest that wild coho salmon and cutthroat trout should out compete farm Atlantic salmon of a similar size in nature. As the relative competitive ability of Atlantic salmon improves when they have a size and residence advantage, should feral populations become established, they may exist on a more equal competitive footing owing to the long freshwater residence of Atlantic salmon.     

Chromosomal differences between European and North American Atlantic salmon discovered by linkage mapping and supported by fluorescence in situ hybridization analysis

ABSTRACT: BACKGROUND: Geographical isolation has generated a distinct difference between Atlantic salmon of European and North American Atlantic origin. The European Atlantic salmon generally has 29 pairs of chromosomes and 74 chromosome arms whereas it has been reported that the North American Atlantic salmon has 27 chromosome pairs and an NF of 72. In order to predict the major chromosomal rearrangements causing these differences, we constructed a dense linkage map for Atlantic salmon of North American origin and compared it with the well-developed map for European Atlantic salmon. RESULTS: The presented male and female genetic maps for the North American subspecies of Atlantic salmon, contains 3,662 SNPs located on 27 linkage groups. The total lengths of the female and male linkage maps were 2,153 cM and 968 cM respectively, with males characteristically showing recombination only at the telomeres. We compared these maps with recently published SNP maps from European Atlantic salmon, and predicted three chromosomal reorganization events that we then tested using fluorescence in situ hybridization (FISH) analysis. The proposed rearrangements, which define the differences in the karyotypes of the North American Atlantic salmon relative to the European Atlantic salmon, include the translocation of the p arm of ssa01 to ssa23 and polymorphic fusions: ssa26 with ssa28, and ssa08 with ssa29. CONCLUSIONS: This study identified major chromosomal differences between European and North American Atlantic salmon. However, while gross structural differences were significant, the order of genetic markers at the fine-resolution scale was remarkably conserved. This is a good indication that information from the International Cooperation to Sequence the Atlantic salmon Genome, which is sequencing a European Atlantic salmon, can be transferred to Atlantic salmon from North America.     

Diet,feeding patterns,and prey selection of subyearling Atlantic salmon (Salmo salar) and subyearling chinook salmon (Oncorhynchus tshawytscha) in a tributary of Lake Ontario

Since juvenile Atlantic salmon (Salmo salar) and Chinook salmon (Oncorhynchus tshawytscha) occupy a similar habitat in Lake Ontario tributaries, we sought to determine the degree of diet similarity between these species in order to assess the potential for interspecific competition. Atlantic salmon, an historically important but currently extirpated component of the Lake Ontario fish community, are the focus of a bi‐national restoration effort. Presently this effort includes the release of hatchery produced juvenile Atlantic salmon in Lake Ontario tributaries. These same tributaries support substantial numbers of naturally reproduced juvenile Pacific salmonids including Chinook salmon. Subyearling Atlantic salmon and subyearling Chinook salmon had significantly different diets during each of the three time periods examined. Atlantic salmon fed slightly more from the benthos than from the drift and consumed mainly chirononmids (47.0%) and ephemeropterans (21.1%). The diet of subyearling Chinook salmon was more closely associated with the drift and consisted mainly of chironomids (60.2%) and terrestrial invertebrates (16.0%). Low diet similarity between subyearling Atlantic salmon and subyearling Chinook salmon likely minimizes competitive interactions for food between these species in Lake Ontario tributaries. However, the availability of small prey such as chironomids which comprise over 50% of the diet of each species, soon after emergence, could constitute a short term resource limitation. To our knowledge this is the first study of interspecific diet associations between these two important salmonid species.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

Characterization of proteases in the skin mucus of Atlantic salmon (Salmo salar) infected with the salmon louse (Lepeophtheirus salmonis) and in whole-body louse homogenate

As part of an investigation of the biochemical interactions between the salmon louse Lepeophtheirus salmonis and Atlantic salmon Salmo salar, we characterized protease activity in the skin mucus of noninfected Atlantic salmon and Atlantic salmon infected with L. salmonis and in an L. salmonis whole-body homogenate. Zymography revealed that mucus from infected salmon contained a series of low-molecular-mass (17-22 kDa) serine proteases that were not present in the mucus of noninfected salmon. Based on molecular mass, inhibition studies, and affinity chromatography, the series of proteases was identified as being trypsin-like. Similar proteases were observed in the L. salmonis homogenate and in mucus from noninfected Atlantic salmon following a 1-hr incubation with live L. salmonis. An antibody raised against Atlantic salmon trypsin failed to recognize any proteases in the mucus of noninfected salmon or infected salmon or in the L. salmonis homogenate. Collectively, these findings suggest that the trypsin-like proteases present in the mucus of infected Atlantic salmon were produced by L. salmonis, possibly to aid in feeding and evasion of host immune responses.     

Competition for shelter among over‐wintering signal crayfish and juvenile Atlantic salmon

Three separate effects on refuge use by signal crayfish Pacifastacus leniusculus and Atlantic salmon Salmo salar were examined: (1) the effect on Atlantic salmon of an addition of signal crayfish (doubling the total number of animals), (2) the effect on signal crayfish of an addition of Atlantic salmon and (3) intraspecific compared with interspecific competition, compared by holding total density of animals constant and varying the proportion of signal crayfish and Atlantic salmon in trials. Observations were made during winter, when both species are nocturnal. The proportion of Atlantic salmon sheltering was significantly lower in the presence than in the absence of signal crayfish when the interspecific treatment (Atlantic salmon plus signal crayfish) effected a doubling in density compared to the intraspecific treatment (Atlantic salmon alone). The proportion of signal crayfish sheltering was independent of the presence of Atlantic salmon. When total density was constant, the proportion of Atlantic salmon sheltering was significantly higher in intraspecific (52·8%) than interspecific trials (27·3%). Atlantic salmon out of shelter during the day in winter are believed to be very vulnerable to predators and the capacity for fish to share shelters with one another is known to be very low. Therefore, competition from crayfish for winter shelters may lead to detrimental effects on Atlantic salmon populations.     

Allozyme heterozygosity, date of first feeding and life history strategy in Atlantic salmon

The relations between allozyme heterozygosity, relative date of first feeding and life history strategy in juvenile Atlantic salmon Salmo salar were examined using eggs obtained from a 400 family cross (20 male × 20 female adult Atlantic salmon). Multilocus heterozygosity, through its positive associations with the timing of first feeding and growth rate, was correlated with life history strategy in juvenile Atlantic salmon, albeit under genotype × environmental (temperature, food availability) regulation. Under hatchery conditions, a 10 day difference was observed in the relative date of first feeding between early and late first feeding Atlantic salmon. Early first feeding Atlantic salmon exhibited a significantly higher mean heterozygosity, grew faster at ambient water temperature (April to November) and a significantly higher proportion adopted the early freshwater maturation (age 0+ years, male fish) or early migrant (age 1+ years, mainly female fish) strategies compared to late first feeding Atlantic salmon. Elevated water temperatures over the winter (December to April, >10·5° C) provided additional growth opportunity allowing previously mature male parr (mainly early first feeders) and lower modal group parr (mainly late first feeders) to adopt the early migrant strategy by the following spring.     

Temporal variation in abundance, return rate and life histories of previously spawned Atlantic salmon in a large subarctic river

The 30 year time series analyses revealed large temporal variation in the return rates and a recent increase in abundance of previous spawning Atlantic salmon Salmo salar in the River Teno, northern Scandinavia. The mean proportion of repeat spawners was 7 and 4% in the total Atlantic salmon catch and 9 and 22% in multi‐sea‐winter (MSW) catch component for females and males, respectively. Previous spawners constituted on the average 7% of the catch in mass but up to 20%(31 t) and 30%(19 t) in 2003 and in 2004, respectively. In 1975–2000, the proportion of previous spawners varied between 1 and 6%(3–12% of MSW Atlantic salmon), whereas in 2001–2004, they accounted for 8–21%(16–35% of MSW Atlantic salmon) of the total Atlantic salmon catch. The number of previous spawners in the catch correlated significantly with the preceding numbers of respective 1–3 sea‐winter (SW) maiden Atlantic salmon 2 years earlier. The recent increase in the numbers of 1S1 and 2S1 (1 or 2 years at sea followed by first spawning and 1 year reconditioning period at sea) alternate spawning Atlantic salmon was a consequence of higher numbers of maiden 1SW and 2SW Atlantic salmon in the catches and increased sea temperatures. Similarly, the return rate of 1SW Atlantic salmon to second spawning has improved in recent years. Most previous spawners ascended and were captured early in the fishing season. The smolt and sea‐age combinations of repeat spawners comprised 68 age groups contributing with the annual mean of 15 age groups to the great diversity of the River Teno Atlantic salmon population complex.     

MHC polymorphism and disease resistance in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>); facing pathogens with single expressed major histocompatibility class I and class II loci

Few studies have yet addressed the functional aspects of MHC molecules in fish. To lay the foundation for this, we evaluated the association between disease resistance and MHC class I and class II polymorphism in Atlantic salmon. Standardized disease challenge trials were performed on a semi-wild Atlantic salmon population with subsequent MHC typing and statistical analysis. The pathogens employed were infectious salmon anaemia virus (ISAV) causing infectious salmon anaemia and the Aeromonas salmonicida bacteria causing furunculosis. The material consisted of 1,182 Atlantic salmon from 33 families challenged with A. salmonicida and 1,031 Atlantic salmon from 25 families challenged with ISAV. We found highly significant associations between resistance towards infectious diseases caused by both pathogens and MH class I and class II polymorphism in Atlantic salmon. The observed associations were detected due to independently segregating MH class I and class II single loci, and inclusion of a large number of fish allowing an extensive statistical analysis.     

Susceptibility of rainbow trout Oncorhynchus mykiss,Atlantic salmon Salmo salar and coho salmon Oncorhynchus kisutch to experimental infection with sea lice Lepeophtheirus salmonis

Physiological, immunological and biochemical parameters of blood and mucus, as well as skin histology, were compared in 3 salmonid species (rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon O. kisutch) following experimental infection with sea lice Lepeophtheirus salmonis. The 3 salmonid species were cohabited in order to standardize initial infection conditions. Lice density was significantly reduced on coho salmon within 7 to 14 d, while lice persisted in higher numbers on rainbow trout and Atlantic salmon. Lice matured more slowly on coho salmon than on the other 2 species, and maturation was slightly slower on rainbow trout than on Atlantic salmon. Head kidney macrophages from infected Atlantic salmon had diminished respiratory burst and phagocytic capacity at 14 and 21 d post-infection (dpi), while infected rainbow trout macrophages had reduced respiratory burst and phagocytic capacities at 21 dpi, compared to controls. The slower development of lice, coupled with delayed suppression of immune parameters, suggests that rainbow trout are slightly more resistant to lice than Atlantic salmon. Infected rainbow trout and Atlantic salmon showed increases in mucus lysozyme activities at 1 dpi, which decreased over the rest of the study. Mucus lysozyme activities of infected rainbow trout, however, remained higher than controls over the entire period. Coho salmon lysozyme activities did not increase in infected fish until 21 dpi. Mucus alkaline phosphatase levels were also higher in infected Atlantic salmon compared to controls at 3 and 21 dpi. Low molecular weight (LMW) proteases increased in infected rainbow trout and Atlantic salmon between 14 and 21 dpi. Histological analysis of the outer epithelium revealed mucus cell hypertrophy in rainbow trout and Atlantic salmon following infection. Plasma cortisol, glucose, electrolyte and protein concentrations and hematocrit all remained within physiological limits for each species, with no differences occurring between infected and control fish. Our results demonstrate that significant differences in mucus biochemistry and numbers of L. salmonis occur between these species.     

Tissue astaxanthin and canthaxanthin distribution in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar)

A comparative investigation of tissue carotenoid distribution between rainbow trout, Oncorhynchus mykiss, and Atlantic salmon, Salmo salar, was undertaken to identify the relative efficiency of utilization of astaxanthin and canthaxanthin. Higher apparent digestibility coefficients (ADCs) (96% in trout vs. 28-31% in salmon; P<0.05), and pigment retention efficiencies (11.5-12.5% in trout vs. 5.5% in salmon; P<0.05), for both astaxanthin and canthaxanthin, were observed for rainbow trout. Astaxanthin deposition was higher than canthaxanthin in rainbow trout, while the reverse was true for Atlantic salmon, suggesting species-specificity in carotenoid utilization. The white muscle (95% in trout vs. 93% in salmon) and kidneys (0.5% in trout vs. 0.2% in salmon) represented higher proportions of the total body carotenoid pool in rainbow trout than in Atlantic salmon (P<0.05), whereas the liver was a more important storage organ in Atlantic salmon (2-6% in salmon vs. 0.2% in trout; P<0.05). The liver and kidney appeared to be important sites of carotenoid catabolism based on the relative proportion of the peak chromatogram of the fed carotenoid in both species, with the pyloric caecae and hind gut being more important in Atlantic salmon than in the rainbow trout. Liver catabolism is suspected to be a critical determinant in carotenoid clearance, with higher catabolism expected in Atlantic salmon than in rainbow trout.     

Immunological relationships of an endogenous guinea pig retrovirus with prototype mammalian type B and type D retroviruses.

A retrovirus endogenous to guinea pig cells was earlier shown to be morphologically similar to type B and type D prototype retroviruses. Molecular hybridization techniques were used to show that guinea pig virus nucleotide sequences are endogenous to both domestic (Cavia porcellus) and indigenous (Cavia aperea) guinea pigs, but cannot be detected in the DNA of either other hystricomorph rodents or other mammals tested. Using radioimmunological techniques designed to detect interspecies relationships, the major internal polypeptide of guinea pig virus (p26) was shown to share three different sets of interspecies antigenic determinants with squirrel monkey retrovirus, viper retrovirus, and mouse mammary tumor virus. Thus, guinea pig virus appears to provide an evolutionary link between type B and D retroviruses.     

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.     

Application of alternative models to identify QTL for growth traits in an F2 Duroc x Pietrain pig resource population

Background

Several lines of evidence including allozyme analysis, restriction digest patterns and sequencing of mtDNA as well as mini- and micro-satellite allele frequencies indicate that Atlantic salmon (Salmo salar) from North America and Europe are genetically distinct. These observations are supported by karyotype analysis, which revealed that North American Atlantic salmon have 27 pairs of chromosomes whereas European salmon have 29 pairs. We set out to construct a linkage map for a North American Atlantic salmon family and to compare this map with the well developed map for European Atlantic salmon.

Results

We used microsatellite markers, which had previously been mapped in the two Atlantic salmon SALMAP mapping families from the River Tay, Scotland, to carry out linkage analysis in an Atlantic salmon family (NB1) whose parents were derived from the Saint John River stock in New Brunswick, Canada. As large differences in recombination rates between female and male Atlantic salmon have been noted, separate genetic maps were constructed for each sex. The female linkage map comprises 218 markers in 37 linkage groups while the male map has 226 markers in 28 linkage groups. We combined 280 markers from the female and male maps into 27 composite linkage groups, which correspond to the haploid number of chromosomes in Atlantic salmon from the Western Atlantic.

Conclusions

A comparison of the composite NB1 and SALMAP linkage maps revealed the reason for the difference in the chromosome numbers between European and North American Atlantic salmon: Linkage groups AS-4 and AS-32 in the Scottish salmon, which correspond to chromosomes Ssa-6 and Ssa-22, are combined into a single NB1 linkage group as are linkage groups AS-21 and AS-33 (corresponding to chromosomes Ssa-26 and Ssa-28). The comparison of the linkage maps also suggested some additional chromosomal rearrangements, but it will require finer mapping, potentially using SNPs, to test these predictions. Our results provide the first comparison of the genomic architecture of Atlantic salmon from North America and Europe with respect to chromosome organization.     

Allelic and haplotypic diversity at the major histocompatibility class II within domesticated Australian Atlantic salmon (Salmo salar L.)

Variation within the major histocompatibility (MH) class II alpha gene ( Sasa-DAA ) was compared between domesticated Australian Atlantic salmon and their ancestral Canadian population. The level of Sasa-DAA and MH class II beta gene ( Sasa-DAB ) sequence variation was also examined within the Australian population and compared with that published for European Atlantic salmon populations. In contrast to variation previously reported for non-coding microsatellite loci, a high level of MH class II allelic variation has been maintained within the domesticated Australian populations. Furthermore, a high level of Sasa-DAA and Sasa-DAB allele sequence diversity was also observed and exceeded that reported for other cultured Atlantic salmon populations. The number of Sasa-DAB allele sequences (14) surpassed the number of Sasa-DAA allele sequences (9) to produce 14 unique class II haplotypes. We conclude that the Australian Atlantic salmon populations show high MH class II allelic and haplotypic variation compared with both its ancestral Canadian population and other cultured Atlantic salmon populations.