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.