Significance of side-tributaries and floodplains for Danubian fish populations.
Changes of aquatic biotopes and the natural dynamics of the Danube by human activity were the main cause of fish decline since the 19th century. Several fish species have recently displayed a drastic reduction in their distribution, and some of them are close to extinction. The restoration fo floodplain functions and biotope diversity is essential for the successful management of fish populations. The present paper describes the most important long-term changes of the Middle Danubian hydrosystem due to river regulations and summarizes the main habitat requirements of fish.