MANAGEMENT IMPLICATIONS OF GENETIC DIFFERENTIATION BETWEEN NATIVE AND HATCHERY POPULATIONS OF BROWN TROUT (SALMO-TRUTTA) IN SPAIN

Isozyme electrophoresis was used to assess the amount and distribution of genetic variation among natural populations and hatchery stocks of brown trout (Salmo trutta) in Spain. Genetic variation was found at 19 out of 50 protein coding loci. The hatchery stocks were conspicuously different from the natural populations, and the two groups appeared to represent distinctly divergent evolutionary lineages of brown trout. The hatchery stocks were highly polymorphic but also markedly homogeneous; only 3% of the total genetic variation was explained by stock differences, indicating a common origin for these stocks. In sharp contrast to the hatchery stocks, the natural populations were found to be highly divergent, and more than 60% of their total genetic variability was due to differences between populations. There is evidence indicating impending or actual loss of natural populations by intrusions of fish of hatchery origin or ancestry. In the interest of optimal resource management, we recommend that the indigenous populations of Spain be fully identified and protected, and that the existing hatchery stocks be replaced with local natural populations.