Genetic protein variation and natural selection in Atlantic salmon (Salmo salav, L.) parr

The principal focus of this study was an examination of the relationship between diallelic variation at the MEP-2 * locus and growth and survival in Atlantic salmon parr. In addition, patterns of growth and survival among genotypes at the AAT-I *, IDDH-I * and ZDHP-2 * loci were also examined. Significant differences in growth were found among MEP-2 * genotypes, with * 100/ 100 homozygotes largest in one of two independent comparisons and the * 125/I25 homozygotes largest in the other. No growth differences were observed among genotypes at any other locus. Although no significant differences were found in survival among genotypes at any locus, results of joint analysis of the patterns of growth and survival among MEP-2 * genotypes were consistent with a model of positive size-selective mortality. The demonstration of growth differences among MEP-2 * genotypes in parr and smolts may indicate an association between selection on this locus in fresh water and previously reported differences in sea-age at maturity among MEP-2 * genotypes in Atlantic salmon.     

Genetic variation in haemolytic activity in Atlantic salmon (Salmo salar L.)

Spontaneous and antibody-dependent haemolytic activity against sheep red blood cells (SRBC) has been studied in serum from Atlantic salmon, Salmo salar L. Considerable increase in haemolytic activity was detected when SRBC were sensitized with haemolysin produced in Atlantic salmon. Haemolytic activity was sensitive both to divalent cations and to heat treatment. Significant reduction in haemolytic activity was detected after absorption with SRBC, indicating the presence of natural antibody against SRBC in Atlantic salmon serum. Persistent haemolytic activity of unsensitized SRBC in serum absorbed to remove natural antibodies was found, which suggests the activation of the alternative complement pathway, while the observed increased haemolytic activity in the presence of specific antibody against SRBC suggests activation of the classical complement pathway. Spontaneous and antibody-dependent haemolytic activity were both analysed in absorbed and non-absorbed sera in a family material of Atlantic salmon. The material consisted of 574 fish belonging to 57 fullsib groups within 20 paternal halfsib groups. Fish with signs of sexual maturity generally showed reduced haemolytic activity. Statistically significant effect of sire on the spontaneous haemolytic activity of both absorbed and nonabsorbed serum, and on antibody-dependent activity, provides evidence of significant additive genetic variation in both the alternative and the classical complement activation in Atlantic salmon. Neither on a phenotypical nor on a family basis were the two traits statistically correlated. The estimated heritabilities were 0.2–0.3 with a standard error of approximately 0.1.     

Genetic differentiation among natural European populations of Atlantic salmon, Salmo salar L., from drainages of the Atlantic Ocean

Previously published allelic frequencies at four polymorphic protein coding loci were used as a basis for examining genetic relationships among 19 European populations of Atlantic salmon, Salmo salar L.--exclusive of Baltic drainages--from the Barents Sea to Spain. The data did not support a model of distinct ancestral (e.g. Boreal and Celtic) origins, but were consistent with all populations descending from a single ancestral group within this region with genetically diverged populations drawn together through limited local migrations.     

Spawning behaviour of a farmed escaped female Atlantic salmon (Salmo salar)

Excavation of stranded redds revealed differences in spawning behaviour between farmed and wild Atlantic salmon. The redd of a farmed fish contained more egg pockets (nine v . average of two) and fewer eggs per pocket (averages: 459 v . 707). No other pocket measures differed.     

Migratory and reproductive behaviour of female adult Atlantic salmon, Salmo salar L., in a spawning stream

Migration and spawning behaviour of eight Atlantic salmon adult females were analysed by radio-tracking in relation to the degree of sexual maturity in a spawning tributary of the R. Sélune. Six of them were grilse and four of them were ripe. All the fish migrated upstream until reaching their spawning site at a distance of 4–12 km from the trap. The daily migration rate up to this site was inversely correlated with the length of the female. Spawning occurred in all fish at the same time when the water temperature increased dramatically. Spawning lasted 1–10 days according to the fish. After spawning, females quickly moved downstream only small distances and then stayed in approximately the same location until death. This study concluded that ripeness did not influence behaviour on the spawning migration and describes certain characteristics of the reproductive phase in a spawning tributary.     

Differences in growth between maturing and non-maturing male Atlantic salmon, Salmo salar L., parr

Sibling male Atlantic salmon parr that matured tended to be the larger fish in January, but their monthly specific growth rates between January and July did not differ from those of non-maturing fish. Maturing fish had lower condition factors in March, but greater increases in condition factor during April, exceeding those of non-maturing males by May. In maturing males, feeding rates between July and September, and specific growth rates in August and September, were lower than those of immature fish. Consequently, the mean size of immatures equalled or exceeded that of maturing males by October. Maturation rates were strongly correlated with increases in mean condition factor only during April.     

An electrophysiological study on the effects of pH on olfaction in mature male Atlantic salmon (Salmo salar) parr

The olfactory responses of mature male Atlantic salmon ( Salmo salar L.) parr to known odorants were studied after exposure of the olfactory epithelia to water of varying pH. Electrophysiological recordings from the olfactory epithelia indicated that the responses of fish to both testosterone and urine from ovulated female Atlantic salmon were significantly reduced at pH 5·5 and 4·5 and abolished at pH 3·5. Concentration response studies indicated that at pH 5·5 and 6·5 significantly higher concentrations of testosterone and urine were required to produce the same amplitude responses as controls. Both testosterone and urine have previously been shown to be important chemical cues eliciting behavioural and physiological responses in Atlantic salmon. The results are therefore discussed in relation to the possible sublethal effects of acidification on reproduction and behaviour of Atlantic salmon and the effects on salmonid stocks.     

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.     

Isolation and characterization of variable (GT)n repetitive sequences from Atlantic salmon, Salmo salar L.

Microsatellites are islands of long repeats of mono-, di- or trinucleotides evenly distributed in the eukaryotic genome with an average distance of 50–100 kb. They display a high degree of length polymorphism and heterozygosity at individual loci, making them highly useful as markers in the development of genomic maps of eukaryotes. In the present work, we examined the dinucleotide repeat motif (dG-dT)_n in the Atlantic salmon, Salmo salar L., genome. The frequency of (dG-dT)_n microsatellites in salmon correlates well with earlier published estimations. Cloning and sequencing of 45 salmon microsatellites revealed perfect and imperfect repeats, but no compound microsatellites. The distribution of number of repeat units in salmon microsatellites differ significantly from that of higher vertebrates. Salmon tends to have more long repeat stretches and less intermediate length repeats.     

Genetic markers for Atlantic salmon (Salmo salar L.): single locus inheritance and joint segregation analyses of minisatellite (VNTR) DNA loci

Relatively few genetic markers are available for detailed studies of Atlantic salmon. The detection of 12 distinct minisatellite DNA loci in this species (by 10 Atlantic salmon and brown trout derived probes) and subsequent inheritance analyses in two half-sib families are reported here. Disomic Mendelian inheritance was confirmed at all loci. Only a single aberrant progeny genotype (at Ssa -A60) was observed among 138 progeny screened. None of the loci was sex-linked. The tight linkage association Str -A22/1 with Str -A22/2, previously reported for brown trout, was found to be conserved in the Atlantic salmon genome. An additional male-specific linkage group, Ssa -A34 with Str -A9/2, was also noted. These highly polymorphic loci should find widespread use as chromosomal, individual, familial and, probably, population markers.     

Mating success of alternative maturation phenotypes in male Atlantic salmon,Salmo salar

Summary Mature male parr successfully fertilized eggs of anadromous female Atlantic salmon, Salmo salar, in competition with anadromous males under simulated natural conditions. Mating situations were created in which mature male parr and anadromous males competing for the opportunity to spawn with an anadromous female differed in allelic forms of the same enzyme. Females deposited eggs into a sequence of 3 or 4 eggs nests. The mean proportion of eggs in a redd fertilized by parr increased with increasing numbers of parr present at a redd, reaching 23% at male parr: anadromous male ratios of 20:1. Single male parr fertilized, on average, 5% of the eggs in a redd. The proportion of eggs in an egg nest fertilized by parr also depended upon the order of egg nest construction, such that parr mating success was highest at the initial nest constructed and lowest at the final nest. Parr have relatively high fertilization success for their size when compared with the smaller maturation phenotype of other salmonids.     

The influence of metabolic rate on otolith increment width in Atlantic salmon parr, Salmo salar L.

The influence of metabolic rate on otolith accretion in Atlantic salmon parr was investigated by comparing oxygen consumption rate and increment width in fast and slow growing individuals. Increment width was found to be positively correlated to mean daily oxygen consumption in both fast growing (S1) and slow growing (S2) parr. The results support previous suggestions that a process related to metabolic rate, rather than somatic growth, governs the rate of otolith accretion.     

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.     

A study of temporal genetic variation in a natural population of Atlantic salmon in the River Bush, Northern Ireland

Temporal genetic variation in River Bush Atlantic salmon was low and much less than among geographically discrete samples reported from elsewhere.     

The impact of a brominated flame retardant on smoltification and olfactory function in Atlantic salmon (Salmo salar L.) smolts

Despite a reduction in exploitation of salmon stocks throughout the NE Atlantic, there continues to be a decline in many populations. The factors regulating these populations remain poorly understood, although there is evidence that environmental conditions experienced in freshwater can effect survival in the marine environment. The aim of this study was to investigate the impact of a brominated flame retardant (hexabromocyclododecane, HBCD) on the parr-smolt transformation in juvenile salmon. It is during this pre-adaptive period to marine life that olfactory imprinting to the natal river is considered to occur. Fish were exposed to low levels of HBCD for 30 days over the peak smoltification period in freshwater, and then transferred to clean seawater for 20 days. Fish were sampled weekly to assess changes in some of the physiological parameters associated with smoltification, and olfactory response to conspecific smolt urine was measured using an electro-olfactogram (EOG). Exposure to HBCD did not affect seawater adaptability, although there was some disruption of plasma thyroid hormone levels, as well as a reduction in olfactory function to conspecific smolt urine. The results are discussed in relation to the marine survival and successful homing of adult salmon.     

Otolith calcification in Atlantic salmon parr, Salmo salar L. and its relation to photoperiod and calcium metabolism

Otolith calcification in Atlantic salmon parr, Salmo salar , was investigated using a radioisotope of calcium, ⁴⁵Ca. Otolith calcification was found to be entrained to light-dark cycles in salmon parr, calcium accumulation on to otoliths declining at night and resuming at dawn. The decline in Otolith calcification at night coincided with a diel decline in plasma calcium concentration. The influence of extracellular calcium on otolith increment formation was considered by inducing hypocalcemia. Induced hypocalcemia resulted in a short-term net loss of calcium from the otolith. The results are discussed in relation to previous studies of the role of extracellular calcium in otolith formation.