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Levels of genetic variability at 12 microsatellite loci and 19 single nucleotide polymorphisms in mitochondrial DNA were studied in four farm strains and four wild populations of Atlantic salmon. Within populations, the farm strains showed significantly lower allelic richness and expected heterozygosity than wild populations at the 12 microsatellite loci, but a significantly higher genetic variability with respect to observed number of haplotypes and haplotype diversity in mtDNA. Significant differences in allele- and haplotype-frequencies were observed between farm strains and wild populations, as well as between different farm strains and between different wild populations. The large genetic differentiation at mitochondrial DNA between wild populations (FST = 0.24), suggests that the farm strains attained a high mitochondrial genetic variability when created from different wild populations seven generations ago. A large proportion of this variability remains despite an expected lower effective population size for mitochondrial than nuclear DNA. This is best explained by the particular mating schemes in the breeding programmes, with 2-4 females per male. Our observations suggest that for some genetic polymorphisms farm populations might currently hold equal or higher genetic variability than wild populations, but lower overall genetic variability. In the short-term, genetic interactions between escaped farm salmon and wild salmon might increase genetic variability in wild populations, for some, but not most, genetic polymorphisms. In the long term, further losses of genetic variability in farm populations are expected for all genetic polymorphisms, and genetic variability in wild populations will be reduced if escapes of farm salmon continue. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: A total of 388 Atlantic salmon juveniles of farm, hybrid and wild parentage were challenged in mixed group replicate tanks by intraperitoneal injection of a cell-cultured isolate of the infectious salmon anemia virus (ISAV). The first mortalities were observed 21 days post-challenge and the experiment was terminated after 38 days. No significant differences in timing of mortality or total mortality were observed between experimental groups (mortality across replicates: farm=92%, hybrid=88%, wild=87%). The length frequency distributions of all experimental groups were distinctly bimodal, permitting fish to be putatively characterized as smolts (>12 cm total length) and non-smolts (<12 cm total length). Within all experimental groups, fish <12 cm displayed lower mortality and delayed timing of mortality compared to fish >12 cm. When the presumptive non-smolts of all experimental groups were removed from the data set, no effect of fish size on either mortality or timing of mortality were observed, suggesting that the process of smoltification may influence susceptibility to ISAV. [Copyright &y& Elsevier]

Abstract: Atlantic salmon of wild, hybrid and farmed parentage were established in November 2002 and hatchery-reared up to March 2004. At age 1 +, farmed fish were significantly (F =28.3 P <0.0001) larger than wild fish, with hybrids intermediate (farm=38.1 g, hybrid=29.0 g, wild=21.9 g). A sample of fish from each group was fin clipped, mixed into two replicate tanks, then exposed to experimental challenge with the causative agent of furunculosis, Aeromonas salmonicida subsp. salmonicida via cohabitants. A third tank, containing only hybrids, was challenged with A. salmonicida in order to investigate the effects of individual fish size on susceptibility. Significant differences in mortality were observed among the groups (G =7.9 P <0.022). However, an effect of fish size on mortality was also observed, and, fish representing the three experimental groups were significantly different in size. When this effect was controlled for, initial differences in group-mortality were no longer significant. Consequently, under the given conditions, no significant differences in susceptibility to the bacteria A. salmonicida subsp. salmonicida were observed between salmon of farm, hybrid and wild parentage. [Copyright &y& Elsevier]