Reduction of genetic variability in a hatchery stock of brown trout, Salmo trutta L.

Enzyme gene variability in a lake-dwelling brown trout, Salmo Irulla , population was compared with its hatchery derivative by starch gel electrophoresis. A loss of genetic variability was detected in the hatchery stock founded 16 years ago in comparison to the present day wild stock; of seven originally polymorphic loci ( Aat-4, Ck-l, Gpi-3, G3p-2, Ldh-1, Mclh-2 and Pgm-l ) two, Gpi-3 and Ldh-1 , had become monomorphic. The overall hetero-zygosity was reduced by a third from 6–2% to 4–2%. A comparison between three successive hatchery cohorts indicates a distinction between stock heterogeneity. The decrease in genetic variability is probably attributable to small population size in the founding event with subsequent genetic drift and inadvertent selection during hatchery procedures.