INDICATORS OF INVASION OF MASS CARP SPECIES BY METCERCARIAE OF OPISTHORCHIIDAE FAMILY IN THE LOWER IRTYSH
In the basin of the Lower Irtysh, the most common types of carp fish (Cyprinidae) are ide ( Leuciscus idus ), bream ( Abramis brama ) and roach ( Rutilus rutilus ). The fish caught in the summer 2017 (20 ide specimens of 3+…7+ years old and 61 roach specimens of 1+…6+ years old) were infested by two Opisthorchiidae representatives: opisthorchosis pathogen Opisthorchis felineus and methorhoz pathogen Metorchis bilis, for which they are an intermediate hosts (a definitive host are carnivorous animals and a human). The extent of invasion by metacercariae of O. felineus was 70%, the combined infection with M. bilis - 25%. Species infested only by methorchis were not detected. Bream is invaded only by an opisthorchiasis pathogen (46.1%). Minimal values were registered in roach: degree of invasion by opisthorchis is 31.1%, degree of invasion by methorchisis is 3.3%, combined invasion occurs in 1.6% of fish. Intensity of infestation with metacercariae of O. felineus (specimens per one fish) made in average: at the age of 3+ - 180.4 specimens per one fish; at the age of 4+ - 105; 5+ - 483.4; 6+ - 938; 7+ - 22. M. bilis was registered at the age of 5+ - 8.5 specimens; 6+ - 675; 7+ - 18. In roach, the intensity of invasion of O. felineus per fish was at the age of 3+ - 33.1 specimens; 4+ - 9.3; 5+ - 7.7; 6+ - 5.3. M. bilis in roach was registered since the age of 2+ and amounted to 2 specimens per a fish; 3+ - 25; 6+ - 6. In bream the intensity of infestation of O. felineus is not high and at the age of 3+ it made 2.7; 4+ - 3.3; 5+ - 13; 6+ - 1 per a fish. The maximum abundance index of O. felineus and M. bilis was found in the population of ide and made 316.5 and 35.5 specimens; in roach AI was 21.9 and 0.8, respectively. The population of bream was least affected by opisthorchis (2.3). The high number of parasites proves that the Lower Irtysh basin is a natural seat of opisthorchosis, that is why, in order to prevent opisthorchosis and methorchisis spreading, it is recommended to strengthen the veterinary and sanitary control in places where fish products are processed and sold, as well as to extend activities on publicizing sanitary rules and preventive norms against these infections.