EN
The investigations showed the incidence of S. inermis Plehn in the fry of carps and S. intermedia Ejsmont in crucians. The intermediate host for S. inermis is Radix auricularia L., and for S. intermedia - Limnea stagnalis L. The development of S. inermis larvae lasts in summer about 4 weeks. The circulation of S. inermis in the ponds under investigation is discussed in detail with particular emphasis of fish in vasion episodes and preventive measures against the spread of parasites.