The ecology of freshwater pearl mussel (Margaritifera margaritifera L.) and evaluation of its mortality on locations in the Czech Republic.

The aim of this thesis was to monitor mortality or more precisely population changes of freshwater pearl mussel (Margaritifera margaritifera L.), which settle in oligothropic stream. Brown trout (Salmo trutta morpha fario L.) is the only one fish host of larval stage of freshwater pearl mussel. The counting of the population was pursued at 2 localities: on the Blanice river and on the stream of Lužní potok in the Czech Republic. For general counting of population a net instrument and an optical instrument were used, that enabling to see them. Population of freshwater pear mussel is in decline in all Europe due to many factors like eutrophication, water pollution, etc. Results of work indicated a decline in population of freshwater pearl mussel at the first area about 15,38 % and at the second area about 15,22 % of the stream Lužní potok. There was not recorded a decline on the Blanice river, on the contrary, the number of population was higher. Among others, the habitation of juveniles was recorded at the first area