Electrophoretically detectable genetic variation in natural and hatchery stocks of Atlantic salmon in Finland

To survey the genetic resources of Atlantic salmon (Salmo salar L.) stocks in Finland, an electrophoretic study was made of natural and hatchery stocks. The stocks were compared with the nearest stocks in the USSR, and the effects of hatchery rearing were evaluated. The genetic variation within and between stocks was measured from 20 samples, of which three (Kola, Neva and Onega) were from the USSR. Twenty-five enzyme loci were examined, of which six were polymorphic: AAT-4, IDH-3, ME-3, MDH-3, PGM-1, and SDH-1. The mean heterozygosity of all the populations was 4.2% (1.0-7.2). For the natural salmon stocks of the Arctic Ocean, the mean heterozygosity was 6.3%, for the natural stocks of Atlantic salmon in the Baltic 4.8%, for the hatchery stocks 3.6%, and for the lake salmon (Salmo salar m. sebago Girard) 1.8%. The results are in agreement with the hypothesis that the amount of variation depends on the effective population size and that culture diminishes variation by decreasing the effective population size. All the stocks originating from different rivers differed from each other with statistical significance. The most unique stocks were the River Kola stock and the lake salmon stock from Lake Saimaa. The genetic distances were consistent with the geographic distance between the rivers from which the stocks originated. Stress is laid on the importance in fish culture of maintaining separate stocks and using larger brood stocks.