Nonanadromous Atlantic Salmon Research Articles

Introduction to “Conservation, Ecology, and Evolution of Nonanadromous Atlantic Salmon”

Introduction to “Conservation, Ecology, and Evolution of Nonanadromous Atlantic Salmon”

Life-history variability and conservation status of landlocked Atlantic salmon: an overview

Nonanadromous Atlantic salmon (Salmo salar) exhibit a combination of variation in life history, habitat, and species co-existence matched by few vertebrates. Distributed in eastern North America and northern Europe, habitat ranges from hundreds of metres of river to Europe’s largest lakes. As juveniles, those with access to a lake usually migrate to feed and grow prior to reproduction. Prey such as smelt (Osmerus mordax, Osmerus eperlanus) and vendace (Coregonus albula) facilitate large body size (50–85 cm at maturity) and persistence in high-diversity (>20 fish species) environments; small-bodied salmon (10–30 cm at maturity), relying on insects as prey, coexist with few (fewer than five) other fishes. At maturity, weight varies more than 400-fold (17 to 7200 g) among populations, fecundity more than 150-fold (33 to 5600), and longevity almost fivefold (3 to 14 years). Landlocked salmon are managed to support sustainable fishing, achieve conservation and restoration targets, and mitigate threats; successes are evident but multiple challenges persist. Extraordinary variability in life history coupled with extensive breadth of habitat and species co-existence render landlocked Atlantic salmon singularly impressive from a biodiversity perspective.

Magnetic map in nonanadromous Atlantic salmon

Long-distance migrants, including Pacific salmon (Oncorhynchus spp), can use geomagnetic information to navigate. We tested the hypothesis that a "magnetic map" (i.e., an ability to extract positional information from Earth's magnetic field) also exists in a population of salmon that do not undertake oceanic migrations. This study examined juvenile Atlantic salmon (Salmo salar) originally from a nonanadromous population in Maine transferred ∼60 years ago to a lake in central Oregon. We exposed juveniles to magnetic displacements representative of locations at the latitudinal boundaries of the Pacific salmon oceanic range in the North Pacific and at the periphery of their ancestral oceanic range in the North Atlantic. Orientation differed among the magnetic treatments, indicating that Atlantic salmon detect map information from the geomagnetic field. Despite no recent history of ocean migration, these fish displayed adaptive orientation responses similar to those observed in native Pacific salmonids. These findings indicate that use of map information from the geomagnetic field is a shared ancestral character in the family Salmonidae and is not restricted to populations with anadromous life histories. Lastly, given that Atlantic salmon are transported throughout the world for capture fisheries and aquaculture, such a robust navigational system is of some concern. Escaped individuals may have greater potential to successfully navigate, and thus invade, introduced habitats than previously suspected.

A survey of salmon gill poxvirus (SGPV) in wild salmonids in Norway

In 2016, the Norwegian health monitoring programme for wild salmonids conducted a real-time PCR-based screening for salmon gill poxvirus (SGPV) in anadromous Arctic char (Salvelinus alpinus L.), anadromous and non-anadromous Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.). SGPV was widely distributed in wild Atlantic salmon returning from marine migration. In addition, characteristic gill lesions, including apoptosis, were detected in this species. A low amount of SGPV DNA, as indicated by high Ct-values, was detected in anadromous trout, but only in fish cohabiting with SGPV-positive salmon. SGPV was not detected in trout and salmon from non-anadromous water courses, and thus seems to be primarily linked to the marine environment. This could indicate that trout are not a natural host for the virus. SGPV was not detected in Arctic char but, due to a low sample size, these results are inconclusive. The use of freshwater from anadromous water sources may constitute a risk of introducing SGPV to aquaculture facilities. Moreover, SGPV-infected Atlantic salmon farms will hold considerable potential for virus propagation and spillback to wild populations. This interaction should therefore be further investigated.

Fatty acid and carotenoid composition of eggs from two nonanadromous Atlantic salmon stocks of cultured and wild origin

Two Swedish landlocked (nonanadromous) salmon (Salmo salar) stocks were investigated with the aim of characterising their egg fatty acid (FA) and carotenoid profiles. Fish from one of the stocks were also cultured over the past few decades as part of the Swedish program for genetic preservation, allowing a comparison between the eggs from females on a diet based on lipids of limnic (natural food chain) origin and eggs from females fed an artificial diet of marine origin. No significant differences in the FA profile of the phospholipid (PL) or triacylglycerol (TAG) fraction were found between the two wild stocks. The content of EPA (20:5n-3, eicosapentaenoic acid) in PL fraction was significantly higher in eggs from cultured females (13.0%) compared with eggs from both wild stocks (5.7 and 6.4%). Further, in PL fraction, AA (20:4n-6, arachidonic acid) levels in these eggs were significantly lower (2.4% versus 6.7 and 6.2%). The AA content of the TAG fraction differed greatly between wild (4.4 and 4.9%) and cultured (1.2%) eggs, whereas this fraction showed almost no corresponding difference in EPA content. The level of DHA (22:6n-3, docosahexaenoic acid) did not differ between the two wild stocks or between wild and cultured fish. This was in spite of widely different levels of DHA in the diet. The composition of carotenoids was altered in the cultured eggs which had a higher proportion and higher content (1.16 μ g egg−1) of astaxanthin than the wild eggs (0.56 and 0.62 μg egg−1, respectively). Hatching success varied markedly between wild (>95%) and cultured fish (40–75%). We conclude that changes in the lipid source in the diet of female salmon during gonadal maturation will alter the egg fatty acid composition with an increased risk of disturbances in embryonic development as a consequence. Further, the lack of any difference between wild and cultured females in terms of their egg DHA content indicates that there is a strong genetic influence on levels of this fatty acid in salmon eggs.

Acclimation to seawater of dwarf nonanadromous Atlantic salmon, Salmo salar

The ability of nonanadromous Atlantic salmon to regulate hydromineral balance in seawater was assessed by determining plasma Na+ and Cl− concentrations, gill Na+–K+ ATPase activity levels, and gill chloride-cell length in fish exposed to gradually increasing salinity. Plasma ion levels were much higher in nonanadromous salmon exposed to seawater than in anadromous smolts in the same condition, and in both forms held in fresh water. This indicates a lower level of hypoosmoregulatory ability in the nonanadromous form. The activity of gill Na+–K+ ATPase was low in nonanadromous salmon at the beginning of the experiment but increased in response to elevated external salinity. Mortality approached 100% despite increased enzyme activity levels. Salmon retained in fresh water did not exhibit increased enzyme activity. Anadromous smolts exposed to the same conditions exhibited somewhat elevated yet nonlethal plasma ion concentrations. Gill chloride cells increased in size in salmon exposed to seawater and decreased in size in fish held in fresh water. Hypoosmoregulatory inability and a general suppression of the smolting process in some stocks of nonanadromous salmon may be associated with sexual maturation at a young age. However, this is not universal, since nonanadromous salmon in some other stocks mature later yet show clear evidence of reduced smolting.

Parr–smolt transformation of a nonanadromous population of Atlantic salmon (Salmo salar) in Norway

Morphological and physiological indices of parr–smolt transformation of fish from anadromous and nonanadromous hatchery-reared populations of Atlantic salmon (Salmo salar) were compared. Both anadromous and nonanadromous Atlantic salmon showed a complete smolt colouration and had a similar high gill Na+,K+–ATPase activity (significantly (P < 0.05) different from that of parr), indicating both morphological and physiological aspects of parr–smolt transformation. The evolutionary stability of the parr–smolt transformation of nonanadromous Atlantic salmon is discussed.

Contrasts in development and smolting of genetically distinct sympatric anadromous and nonanadromous Atlantic salmon, Salmo salar

Parameters associated with the parr–smolt transformation were compared in cultured 1+ anadromous and nonanadromous Atlantic salmon derived from wild broodstock collected in Gambo River, Newfoundland. Progeny of nonanadromous salmon were significantly longer at swim-up than progeny of anadromous salmon, although consistent differences in growth performance were not observed during most of the 1 st year of development. Anadromous salmon grew more rapidly than nonanadromous salmon in the spring months during the smolting period. Distinct differences were noted between groups in seasonal levels of body silvering, gill Na+–K+ ATPase activity, and size and number of gill chloride cells. Most male nonanadromous salmon matured as "post-smolts," whereas maturation was not observed among female nonanadromous nor among either sex in the anadromous group. Differences between anadromous and nonanadromous salmon were not observed in seasonal levels of body moisture, plasma Na+ and Cl−, condition factor, or salinity tolerance. Differences noted between groups are probably genetic in nature and suggest that the two forms of salmon in Gambo River represent separate breeding populations.

Mitochondrial DNA Variation Reveals Genetically Distinct Sympatric Populations of Anadromous and Nonanadromous Atlantic Salmon,Salmo salar

Mitochondrial DNA variation was surveyed among wild anadromous and nonanadromous Atlantic salmon, Salmo salar, which occur in sympatry in Gambo River, Newfoundland. Seventy-one salmon were screened with 18 restriction enzymes, 5 of which revealed nucleotide sequence variation. Nucleotide sequence divergence estimates among the four distinct genotypes detected ranged from 0.2 to 1.0%. Significant heterogeneity in mtDNA genotype frequencies supports the view that exchange of breeding females between groups is infrequent or does not occur, an inference consistent with the observation that the forms use separate spawning sites within the system. Mitochondrial DNA diversity was somewhat greater among the nonanadromous salmon than the anadromous salmon (nucleon diversity (h) = 0.37 and 0.52, respectively). Potential mechanisms for maintaining reproductive isolation include selection of different spawning habitats, different spawning times, and sexual selection based upon the size difference between the two forms.

Genetic Divergence of Anadromous and Nonanadromous Atlantic Salmon (Salmo salar) in the River Namsen, Norway

Anadromous and nonanadromous Atlantic salmon, Salmo salar, coexist in the River Namsen in Norway. We studied genetic divergence between these two life history types by using electrophoretic data from 38 protein loci. Although allele frequencies differed significantly between the types at four loci no fixed allele frequency difference was observed. Nei's genetic distance between the life history types, however, was 0.01 a relatively high value for Atlantic salmon populations. The genetic differences observed between anadromous and nonanadromous salmon accounted for 18.3% of the total gene diversity. The five nonanadromous salmon samples formed two genetically different groups corresponding to the upper and lower ranges of the nonanadromous salmon in the river. The average observed heterozygosity was 3.1% for anadromous and 1.0% for nonanadromous salmon. The low heterozygosity in nonanadromous salmon probably reflects a strong founder effect. Stockings of large numbers of anadromous salmon fry to the upper reaches of the River Namsen have caused no detectable hybridization with nonanadromous salmon. Also downstream migrating nonanadromous salmon have apparently not made any important genetic contribution to the anadromous fish.

Parr–Smolt Transformation in Female and Sexually Mature Male Anadromous and Nonanadromous Atlantic Salmon,Salmo salar

The parr–smolt transformation was compared in cultured Newfoundland male and female anadromous and nonanadromous Atlantic salmon, Salmo salar. Seasonal patterns of decreasing total lipid content and condition factor accompanied by increasing moisture content, silvering, and branchial Na+-K+ATPase activity indicate that smoltification occurred only in immature anadromous females. Previously mature anadromous males did not smoitify. In general, smoltification did not occur in nonanadromous salmon. Chloride cell length did not increase in any group with smoltification. The lack of smoltification in previously mature male parr of anadromous stock is consistent with reports of small numbers of male salmon in smolt runs in many Newfoundland rivers.

Analysis of mitochondrial DNA in allopatric anadromous and nonanadromous Atlantic salmon, Salmo salar

Analysis of mitochondrial DNA from allopatric anadromous and nonanadromous Atlantic salmon was conducted using restriction endonucleases. A variant fragment pattern was produced in a single nonanadromous specimen by one restriction enzyme. Fragment patterns produced by all other enzymes did not reveal any variation between or within populations. These results support the hypothesis that the two forms of salmon are very closely related.

Mating between anadromous and nonanadromous Atlantic salmon, Salmo salar

Mating experiments were conducted to determine whether behavioural isolating mechanisms exist that would prevent interbreeding between anadromous and nonanadromous Atlantic salmon, Salmo salar. Males of both forms attempted to stimulate females of the other form to spawn and females responded by digging redds, spawning, and covering redds. Viable eggs were produced in both cases. These forms probably represent within-population phenotypic variation where they co-occur. Interbreeding can be expected if anadromous salmon are introduced into areas formerly occupied only by the nonanadromous form.