Lebensraumänderungen in Fließgewässern eine fischbiologische Perspektive

Although fish show a high capacity for adaptation to almost all types of aquatic habitat, they are suffering worldwide from habitat alteration and habitat destruetion that inevitably results in species loss and reduced biodiversity. In Switzeriand, the number of streams capable of supporting natural fish assemblages - populations that are products of a natural stream system - has been dwindling dramatically in the last decades. This is due to stream straightening, channelization, and intensive hydroelectric power generation. The main adverse effeets of these impacts on fish species (Ioss of species, decline of population) are discussed in the present article. In this context the focus will be on longitudinal connectivity and related problems of fish migrationl dispersal. Fisheries management also influences the biodiversity of fish. Fish stocking of non-Iocal strains results in negative effeets on genetic diversity of the loeal population, while the introduction of non-native species can displace native species. Such interrelations are iIIustrated for rivers in the Alpine Rhine valley.