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Anonymous (1999). A comparison of genetic variability in artificial and natural populations of brown trout in a regulated river system. Regulated Rivers: Research and Management. 15:159-168.

Brown trout Salmo trutta were sampled from tributaries of Glomma, the largest river system in Norway. Brown trout were formerly known to migrate long distances, but several dams and river regulations have made migration difficult, as fishways constructed at the dams are not efficient. To compensate for the resultant reduction in brown trout, the river system has been stocked with hatchery fish reared from native brown trout. Genetic analysis by enzyme electrophoresis was conducted to monitor possible genetic effects on native fish. Brown trout were obtained from a fishway at Lopet in the South Rena River, and from a section at Deset, 16 km upstream of the fishway. One sample was taken from a cohort of first generation hatchery fish, based on only six spawning fish collected in the fishway, and one sample was taken from the second hatchery generation, bred from a mixture of two cohorts of first generation hatchery fish. The pooled broodstock of these two first generation cohorts numbered five females and five males. Eight samples were taken from second-, third- and fourth-order streams containing populations differing in size and degree of isolation. Tissue samples taken from eye, liver and muscle were analyzed using starch gel electrophoresis for protein polymorphism to determine genetic population structures. Allele frequencies, heterozygosity and polymorphism were compared. The fraction of heterozygosity ranged from 3.3 to 13.5% in the wild populations, and the lowest fraction was found in the most isolated population. Heterozygosity was 8.0% in the first generation of hatchery reared fish and 7.3% in the second generation. The number of detected polymorphic loci ranged from one to seven, with a mean of 4.5, in wild populations, but was three in the first generation and four in the second generation of hatchery fish. Polymorphism seemed to be lost at three loci in the first generation, but one locus was restored in the second generation, probably due to breeding with another hatchery cohort.