EN
Changes in infection and distribution of parasites in fish of different length (age) were analyzed. It was found that most parasites colonized fish during the first weeks of their sojourn in the ponds, but only some of these species remained in fish in the second and third years of their life. Protozoans appeared to be mainly associated with fry; the occurrence of some dactylogyrids decreased with increasing fish length, others showed the opposite tendency; ectoparasitic crustaceans and leeches showed preference to bigger fish. The probable reasons for these phenomena are discussed.