Fittness reducing effect of parasitic infections to fish microhabitat preferences in the process of new river bed settlement.

The high flow ambivalency connected with the extreme water levels, and the floods consequent upon this, are due to the global climate changes. The main method used to solve this problem is still - especially in urbanized area - river regulation. To the contrary, in developed countries, the different way of solution - renaturation of canalized rivers can be observed. In both cases, the responses of biota on the habitat changes is not predictable, but very questionable. Channel shift of the nearly 3 km long section of river Nitra and its Handlovka tributary, as the consequence of the local mining activities, serves the unique natural experiment to biologists and ecologists, hardly to simulate in the laboratory conditions. Definitely, investigation and monitoring of such unusual processes „in medias res“ is the first step to make the well-founded prognosis and correct decisions in future related river regulations.