A POLYMORPHISM IN THE RIBOSOMAL-RNA GENES DISTINGUISHES ATLANTIC SALMON (SALMO-SALAR) FROM NORTH-AMERICA AND EUROPE

There is good evidence to suggest that Atlantic salmon (Salmo salar) from North America and Europe form distinct breeding populations. However, it has been very difficult to discover a genetic marker that allows the continent of origin of an individual salmon to be determined unambiguously. Repetitive elements in the nuclear genome have provided population-specific markers in several species. Therefore, we examined the ribosomal RNA gene (rDNA) complex in Atlantic salmon by Southern blot analysis using a cloned repeating unit of the Drosophila melanogaster rDNA as a probe. A restriction fragment length polymorphism that could distinguish between salmon from Newfoundland and Scotland was detected using a combination of the restriction enzymes Sacl and Xbal. The Newfoundland salmon had additional fragments of 3.6 kilobase pairs (kbp) and 2.6 kbp. Of 27 salmon from 10 populations in Europe, none possessed the 3.6- or the 2.6-kbp fragment whereas all 33 North American Atlantic salmon (from six populations) had the 2.6-kbp band and the majority showed the 3.6-kbp fragment. This preliminary survey strongly suggests that this genetic marker can be used to identify the continent of origin of individual Atlantic salmon.