GENETIC-CHARACTERIZATION OF ATLANTIC SALMON (SALMO-SALAR) LINES FARMED IN IRELAND

Five reared lines of Atlantic salmon, Salmo salar L., constituted over 90% of the smolt production of the Irish farming industry in 1990. They were assayed for the six polymorphic enzyme loci, which contribute most of the reported electrophoretically-detectable variation in the enzymes of S. salar. The lines, four of Norwegian and one of chiefly Scottish origin, were sampled as parr in late 1989 and early 1990. Mean heterozygosity (HBAR) and mean number of alleles per locus (N(a)BAR) in the most popular farmed line were comparable to the values observed in wild Irish populations, but the other lines had lower values. It seems likely that genetic variability in the latter lines has been decreased by management practices, though it should be noted that wild donor populations were not investigated. The five reared lines analysed differed significantly from each other in genetic composition, despite the fact that four lines originated from the same Norwegian source. The probability that many sub-groups of the major farmed lines differ from each other genetically is suggested and the implications for genetic investigations of escape incidents is discussed.