Failure of a stocking policy, of hatchery reared brown trout, Salmo trutta L., in Asturias, Spain, detected using LDH‐5* as a genetic marker

A useful genetic marker exists through the apparent fixation of the LDH‐5 * 100 allele in wild populations of brown trout in rivers from Asturias, Spain, contrasted with the near fixation of the LDH‐5 * 90 allele in hatchery populations used to stock these rivers. In sampling locations where natural reproduction occurred, the * 100 allele was found exclusively in all areas having no record of hatchery stocking. The * 100 allele also predominated in three stocked areas having natural reproduction; in two of these areas a few individuals of the 0 + age class were homozygous for the * 90 allele. These data indicated that all catchable and reproductive fish originated from indigenous populations and thus the policy of hatchery supplementation was a failure in these areas.