Stocking impact and allozyme diversity in brown trout from Mediterranean southern France

Analysis of trout from 13 stations on the Mediterranean slopes of the Frenc h Pyrenees by 31 presumptive enzyme loci demonstrated the major impact of r estocking programmes. Although the annual introgression resulting from thes e introductions was small, the accumulation of genes of Atlantic origin has resulted in a change in allele frequencies. Genetic disequilibria within a nd between loci exist. Introgression by genes of domestic (hatchery) origin varied from 0 to 77% among stations. Natural Mediterranean populations sho w no detectable geographical structure. There was a direct relation between the degree of introgression and heterozygosity. However, restocking could not explain all of the observed genetic disequilibria. (C) 2000 The Fisheri es Society of the British Isles.