Fish stocking is a common management practice to enhance local fisheries or to support threatened species. The pros and cons of stocking are a hotly debated issue because neither the impact nor the fate of stocked fish in nature can be easily predicted. From an evolutionary perspective, fish stocking represents a large scale experiment in which foreign, potentially maladapted, individuals are introduced and removed by selection. An analysis of the fitness of stocked fish is thus attractive for managers to optimize the use of available resources, but also for basic research to learn about local adaptation and the genetics of fitness differences. I participate in genetic analysis to evaluate stocking practices in stocked zander (Sander lucioperca) and pike (Esox lucius) with Dr. Erik Eschbach and Prof. Dr. Robert Arlinghaus (both IGB, Berlin, Germany).