Because of the lack of information on the genetic structure of fishes on the Belgian Continental Shelf, the Laboratory of Aquatic Ecology of the Katholieke Universiteit Leuven prolonged the large-scale survey of the genetic structure of selected marine animals. Species were chosen on the basis of their abundance and role in the food web (gobies of the genus Pomatoschistus), as ecological indicator (parasites of the flatworm genus Gyrodactylus) or their significance for fisheries (European eel and sole). The genetic structure of sole (Solea solea) points to isolation by distance as measured with mitochondrial markers.