SURVIVING FRAGMENTS OF A CHONDROSTOMA-NASUS POPULATION UNDER EXTREME CONDITIONS IN THE MOHELNO RESERVOIR (CZECH-REPUBLIC)

Under the extreme hydrological conditions of the Mohelno Reservoir, wi th enormous diurnal fluctuations of the water level and with a high co efficient of anual water exchanges, remnants of the original river pop ulation of nase Chondrostoma nasus are regularly observed. These fragm ents of the native population of this species have survived in the res ervoir up to the present, despite disruption of the river continuum 17 -18 years ago. Even when C. nasus specimens were found in full spawnin g condition, the natural reproduction failed due to extreme water leve l fluctuations (of 10 m and more daily). The results document that adu lt individuals of C. nasus demonstrate a markedly high resistance to e xtreme conditions of the reservoir environment.