Stocking, pollution and river network partitioning in the genetic structures of fish populations: The European grayling, Thymallus thymallus, along the Rhone River section bordering Savoy, France.

Allozymic variability was examined in the European grayling populations from the River Rhone and its tributaries along the border of Savoy, France. Large differences appeared between these populations despite their vicinity. Within-population variability appeared to be mainly due to the introgression of foreign genes because of the stocking performed for many years. The between-population differences rather seem to be due to a regulation of the genetic impact of stocking by the environmental conditions. The deterioration of the physical conditions and the river bed partitionning by the dams, associated with a drastic pollution event, appeared to be the key factors of the genetic patterns observed. If so, these would be entirely man-made.