Résumé
Agricultural development modified the connectivity of the Rhone River delta waterbodies (also called the Camargue) which is now isolated from the Rhone River by dikes. Furthermore, the hydrographic network of the Camargue is constituted of irrigation and drainage canals, which are not directly connected. Pikeperch (Sander lucioperca L.), an allochthonous freshwater species, colonised the Rhone and the Camargue more than 50 years ago. We used morphometric and meristic features, otolith shape descriptors and protein electrophoresis in order to assess whether the Camargue houses one or several pikeperch populations. All characters except the meristic counts highlighted the existence of two subpopulations: one in the drainage network and one in the irrigation network. Electrophoresis showed that the irrigation network population is closer to the Rhone population and that the drainage network population displayed a high inbreeding rate. The causes of such isolation and the implications for the pikeperch population dynamics are discussed.