• genetics;
  • brown trout;
  • wild;
  • hatchery;
  • colonization

Biochemical genetic variation in populations of anadromous and resident brown trout, Salmo trutta L., was studied. Altogether 50 Norwegian populations were screened for 32 enzyme loci. Genetic polymorphism was found at the following 11 loci: AAT-4* (E.C., CK-1* (E.C., G3PDH-2* (E.C., IDHP-2* (E.C., LDH-5* (E.C., MDH-2* (E.C., MDH-3/4* (E.C., MEP-2* (E.C., GPI-2* (E.C. GPI-5* (E.C. and PGM-1* (E.C., giving an overall polymorphism of 34%, ranging from 3.7 to 29.6% among individual populations. The average calculated heterozygosity ranged from 1.4 to 10.2% among populations. Genetic heterogeneity was observed among anadromous populations, and significant differences in allelic frequencies were found between anadromous populations in neighbouring watercourses, among resident populations and between anadromous and resident populations inhabiting the same watercourses. Significant heterogeneity was also found among 12 populations from Lake Mjøsa, with a major division between the western and eastern populations of the lake. Differences in allelic frequencies were found between wild stocks and their hatchery derivatives, and between different hatchery derivatives originating from the same wild population. In some cases release of hatchery populations into wild stocks may have influenced the genetic characteristics of wild stocks. The data support the hypothesis of eastern as well as western postglacial colonization lines for Norwegian brown trout.